add Validator interface and DefaultAccessibilityValidator

refactor for cleaner implementation

Change-Id: I6ba13c5a46e444806f492bc7de365405fecae0d5

32 files changed, 629 insertions, 811 deletions

diff --git a/src/com/google/android/droiddriver/UiElement.java b/src/com/google/android/droiddriver/UiElement.java
index fc75e5b..71b43ed 100644
--- a/src/com/google/android/droiddriver/UiElement.java
+++ b/src/com/google/android/droiddriver/UiElement.java
@@ -19,7 +19,7 @@ package com.google.android.droiddriver;
 import android.graphics.Rect;
 
 import com.google.android.droiddriver.actions.Action;
-import com.google.android.droiddriver.exceptions.ElementNotVisibleException;
+import com.google.android.droiddriver.actions.InputInjector;
 import com.google.android.droiddriver.finders.Attribute;
 import com.google.android.droiddriver.finders.Predicate;
 import com.google.android.droiddriver.instrumentation.InstrumentationDriver;
@@ -140,7 +140,6 @@ public interface UiElement {
    * Executes the given action.
    *
    * @param action The action to execute
-   * @throws ElementNotVisibleException when the element is not visible
    * @return true if the action is successful
    */
   boolean perform(Action action);
@@ -149,31 +148,24 @@ public interface UiElement {
    * Sets the text of this element.
    *
    * @param text The text to enter.
-   * @throws ElementNotVisibleException when the element is not visible
    */
   void setText(String text);
 
   /**
    * Clicks this element. The click will be at the center of the visible
    * element.
-   *
-   * @throws ElementNotVisibleException when the element is not visible
    */
   void click();
 
   /**
    * Long-clicks this element. The click will be at the center of the visible
    * element.
-   *
-   * @throws ElementNotVisibleException when the element is not visible
    */
   void longClick();
 
   /**
    * Double-clicks this element. The click will be at the center of the visible
    * element.
-   *
-   * @throws ElementNotVisibleException when the element is not visible
    */
   void doubleClick();
 
@@ -182,7 +174,6 @@ public interface UiElement {
    *
    * @param direction specifies where the view port will move, instead of the
    *        finger.
-   * @throws ElementNotVisibleException when the element is not visible
    */
   void scroll(PhysicalDirection direction);
 
@@ -228,4 +219,9 @@ public interface UiElement {
    * Gets the parent.
    */
   UiElement getParent();
+
+  /**
+   * Gets the {@link InputInjector} for injecting InputEvent.
+   */
+  InputInjector getInjector();
 }
diff --git a/src/com/google/android/droiddriver/actions/EventAction.java b/src/com/google/android/droiddriver/actions/EventAction.java
index 71ceb6f..f2736e3 100644
--- a/src/com/google/android/droiddriver/actions/EventAction.java
+++ b/src/com/google/android/droiddriver/actions/EventAction.java
@@ -19,7 +19,6 @@ package com.google.android.droiddriver.actions;
 import android.view.InputEvent;
 
 import com.google.android.droiddriver.UiElement;
-import com.google.android.droiddriver.base.BaseUiElement;
 
 /**
  * Implements {@link Action} by injecting synthesized events.
@@ -31,7 +30,7 @@ public abstract class EventAction extends BaseAction {
 
   @Override
   public boolean perform(UiElement element) {
-    return perform(((BaseUiElement) element).getInjector(), element);
+    return perform(element.getInjector(), element);
   }
 
   /**
diff --git a/src/com/google/android/droiddriver/actions/EventUiElementActor.java b/src/com/google/android/droiddriver/actions/EventUiElementActor.java
index dbee143..1913e5d 100644
--- a/src/com/google/android/droiddriver/actions/EventUiElementActor.java
+++ b/src/com/google/android/droiddriver/actions/EventUiElementActor.java
@@ -17,7 +17,6 @@
 package com.google.android.droiddriver.actions;
 
 import com.google.android.droiddriver.UiElement;
-import com.google.android.droiddriver.base.UiElementActor;
 import com.google.android.droiddriver.scroll.Direction.PhysicalDirection;
 
 /**
diff --git a/src/com/google/android/droiddriver/base/UiElementActor.java b/src/com/google/android/droiddriver/actions/UiElementActor.java
index b7ffe47..abca286 100644
--- a/src/com/google/android/droiddriver/base/UiElementActor.java
+++ b/src/com/google/android/droiddriver/actions/UiElementActor.java
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package com.google.android.droiddriver.base;
+package com.google.android.droiddriver.actions;
 
 import com.google.android.droiddriver.UiElement;
 import com.google.android.droiddriver.scroll.Direction.PhysicalDirection;
diff --git a/src/com/google/android/droiddriver/actions/accessibility/AccessibilityAction.java b/src/com/google/android/droiddriver/actions/accessibility/AccessibilityAction.java
index 4d47eac..5edc131 100644
--- a/src/com/google/android/droiddriver/actions/accessibility/AccessibilityAction.java
+++ b/src/com/google/android/droiddriver/actions/accessibility/AccessibilityAction.java
@@ -21,7 +21,7 @@ import android.view.accessibility.AccessibilityNodeInfo;
 import com.google.android.droiddriver.UiElement;
 import com.google.android.droiddriver.actions.Action;
 import com.google.android.droiddriver.actions.BaseAction;
-import com.google.android.droiddriver.uiautomation.base.BaseUiAutomationElement;
+import com.google.android.droiddriver.uiautomation.UiAutomationElement;
 
 /**
  * Implements {@link Action} via the Accessibility API.
@@ -33,7 +33,7 @@ public abstract class AccessibilityAction extends BaseAction {
 
   @Override
   public boolean perform(UiElement element) {
-    return perform(((BaseUiAutomationElement<?>) element).getNode(), element);
+    return perform(((UiAutomationElement) element).getRawElement(), element);
   }
 
   /**
diff --git a/src/com/google/android/droiddriver/actions/accessibility/AccessibilityClickAction.java b/src/com/google/android/droiddriver/actions/accessibility/AccessibilityClickAction.java
index 4a4033c..0e7cc2b 100644
--- a/src/com/google/android/droiddriver/actions/accessibility/AccessibilityClickAction.java
+++ b/src/com/google/android/droiddriver/actions/accessibility/AccessibilityClickAction.java
@@ -22,7 +22,7 @@ import com.google.android.droiddriver.UiElement;
 import com.google.android.droiddriver.exceptions.ActionException;
 
 /**
- * An {@link AccessibilityAction} that clicks on an UiElement.
+ * An {@link AccessibilityAction} that clicks on a UiElement.
  */
 public abstract class AccessibilityClickAction extends AccessibilityAction {
 
diff --git a/src/com/google/android/droiddriver/actions/accessibility/AccessibilityUiElementActor.java b/src/com/google/android/droiddriver/actions/accessibility/AccessibilityUiElementActor.java
index 491ad7a..dec5979 100644
--- a/src/com/google/android/droiddriver/actions/accessibility/AccessibilityUiElementActor.java
+++ b/src/com/google/android/droiddriver/actions/accessibility/AccessibilityUiElementActor.java
@@ -18,7 +18,7 @@ package com.google.android.droiddriver.actions.accessibility;
 
 import com.google.android.droiddriver.UiElement;
 import com.google.android.droiddriver.actions.TextAction;
-import com.google.android.droiddriver.base.UiElementActor;
+import com.google.android.droiddriver.actions.UiElementActor;
 import com.google.android.droiddriver.scroll.Direction.PhysicalDirection;
 
 /**
diff --git a/src/com/google/android/droiddriver/base/BaseDroidDriver.java b/src/com/google/android/droiddriver/base/BaseDroidDriver.java
index 4776a66..b881b91 100644
--- a/src/com/google/android/droiddriver/base/BaseDroidDriver.java
+++ b/src/com/google/android/droiddriver/base/BaseDroidDriver.java
@@ -19,6 +19,7 @@ package com.google.android.droiddriver.base;
 import com.google.android.droiddriver.DroidDriver;
 import com.google.android.droiddriver.Poller;
 import com.google.android.droiddriver.UiElement;
+import com.google.android.droiddriver.actions.InputInjector;
 import com.google.android.droiddriver.exceptions.ElementNotFoundException;
 import com.google.android.droiddriver.exceptions.TimeoutException;
 import com.google.android.droiddriver.finders.ByXPath;
@@ -28,10 +29,10 @@ import com.google.android.droiddriver.util.Logs;
 /**
  * Base DroidDriver that implements the common operations.
  */
-public abstract class BaseDroidDriver implements DroidDriver {
+public abstract class BaseDroidDriver<R, E extends BaseUiElement<R, E>> implements DroidDriver {
 
   private Poller poller = new DefaultPoller();
-  private BaseUiElement rootElement;
+  private E rootElement;
 
   @Override
   public UiElement find(Finder finder) {
@@ -88,11 +89,16 @@ public abstract class BaseDroidDriver implements DroidDriver {
     this.poller = poller;
   }
 
-  protected abstract BaseUiElement getNewRootElement();
+  public abstract InputInjector getInjector();
 
-  protected abstract DroidDriverContext getContext();
+  protected abstract E newRootElement();
 
-  protected BaseUiElement getRootElement() {
+  /**
+   * Returns a new UiElement of type {@code E}.
+   */
+  protected abstract E newUiElement(R rawElement, E parent);
+
+  public E getRootElement() {
     if (rootElement == null) {
       refreshUiElementTree();
     }
@@ -101,8 +107,7 @@ public abstract class BaseDroidDriver implements DroidDriver {
 
   @Override
   public void refreshUiElementTree() {
-    getContext().clearData();
-    rootElement = getNewRootElement();
+    rootElement = newRootElement();
   }
 
   @Override
diff --git a/src/com/google/android/droiddriver/base/BaseUiDevice.java b/src/com/google/android/droiddriver/base/BaseUiDevice.java
index 21e8aae..2ca501d 100644
--- a/src/com/google/android/droiddriver/base/BaseUiDevice.java
+++ b/src/com/google/android/droiddriver/base/BaseUiDevice.java
@@ -56,7 +56,7 @@ public abstract class BaseUiDevice implements UiDevice {
     if (!isScreenOn()) {
       // Cannot call perform(POWER_ON) because perform() checks the UiElement is
       // visible.
-      POWER_ON.perform(getContext().getInjector(), null);
+      POWER_ON.perform(getContext().getDriver().getInjector(), null);
       getContext().tryWaitForIdleSync(POWER_ON.getTimeoutMillis());
     }
   }
@@ -112,5 +112,5 @@ public abstract class BaseUiDevice implements UiDevice {
 
   protected abstract Bitmap takeScreenshot();
 
-  protected abstract DroidDriverContext getContext();
+  protected abstract DroidDriverContext<?, ?> getContext();
 }
diff --git a/src/com/google/android/droiddriver/base/BaseUiElement.java b/src/com/google/android/droiddriver/base/BaseUiElement.java
index ba25874..340f649 100644
--- a/src/com/google/android/droiddriver/base/BaseUiElement.java
+++ b/src/com/google/android/droiddriver/base/BaseUiElement.java
@@ -20,9 +20,9 @@ import android.graphics.Rect;
 
 import com.google.android.droiddriver.UiElement;
 import com.google.android.droiddriver.actions.Action;
-import com.google.android.droiddriver.actions.InputInjector;
+import com.google.android.droiddriver.actions.EventUiElementActor;
+import com.google.android.droiddriver.actions.UiElementActor;
 import com.google.android.droiddriver.exceptions.DroidDriverException;
-import com.google.android.droiddriver.exceptions.ElementNotVisibleException;
 import com.google.android.droiddriver.finders.Attribute;
 import com.google.android.droiddriver.finders.Predicate;
 import com.google.android.droiddriver.finders.Predicates;
@@ -30,6 +30,7 @@ import com.google.android.droiddriver.scroll.Direction.PhysicalDirection;
 import com.google.android.droiddriver.util.Logs;
 import com.google.android.droiddriver.util.Strings;
 import com.google.android.droiddriver.util.Strings.ToStringHelper;
+import com.google.android.droiddriver.validators.Validator;
 
 import java.util.ArrayList;
 import java.util.Collections;
@@ -41,18 +42,19 @@ import java.util.concurrent.FutureTask;
 
 /**
  * Base UiElement that implements the common operations.
+ *
+ * @param <R> the type of the raw element this class wraps, for example, View or
+ *        AccessibilityNodeInfo
+ * @param <E> the type of the concrete subclass of BaseUiElement
  */
-public abstract class BaseUiElement implements UiElement {
+public abstract class BaseUiElement<R, E extends BaseUiElement<R, E>> implements UiElement {
   // These two attribute names are used for debugging only.
   // The two constants are used internally and must match to-uiautomator.xsl.
   public static final String ATTRIB_VISIBLE_BOUNDS = "VisibleBounds";
   public static final String ATTRIB_NOT_VISIBLE = "NotVisible";
 
-  private final UiElementActor uiElementActor;
-
-  protected BaseUiElement(UiElementActor UiElementActor) {
-    this.uiElementActor = UiElementActor;
-  }
+  private UiElementActor uiElementActor = EventUiElementActor.INSTANCE;
+  private Validator[] validators = {};
 
   @SuppressWarnings("unchecked")
   @Override
@@ -158,15 +160,14 @@ public abstract class BaseUiElement implements UiElement {
     return selectionStart >= 0 && selectionStart != selectionEnd;
   }
 
-  /**
-   * Gets the {@link InputInjector} for injecting InputEvent.
-   */
-  public abstract InputInjector getInjector();
-
   @Override
   public boolean perform(Action action) {
     Logs.call(this, "perform", action);
-    checkVisible();
+    for (Validator validator : validators) {
+      if (!validator.isValid(this)) {
+        throw new DroidDriverException(validator + " failed");
+      }
+    }
     return performAndWait(action);
   }
 
@@ -229,17 +230,11 @@ public abstract class BaseUiElement implements UiElement {
 
   protected abstract Map<Attribute, Object> getAttributes();
 
-  protected abstract List<? extends BaseUiElement> getChildren();
-
-  private void checkVisible() {
-    if (!isVisible()) {
-      throw new ElementNotVisibleException(this);
-    }
-  }
+  protected abstract List<E> getChildren();
 
   @Override
-  public List<? extends BaseUiElement> getChildren(Predicate<? super UiElement> predicate) {
-    List<? extends BaseUiElement> children = getChildren();
+  public List<E> getChildren(Predicate<? super UiElement> predicate) {
+    List<E> children = getChildren();
     if (children == null) {
       return Collections.emptyList();
     }
@@ -247,8 +242,8 @@ public abstract class BaseUiElement implements UiElement {
       return children;
     }
 
-    List<BaseUiElement> filteredChildren = new ArrayList<BaseUiElement>(children.size());
-    for (BaseUiElement child : children) {
+    List<E> filteredChildren = new ArrayList<E>(children.size());
+    for (E child : children) {
       if (predicate.apply(child)) {
         filteredChildren.add(child);
       }
@@ -283,4 +278,20 @@ public abstract class BaseUiElement implements UiElement {
       }
     }
   }
+
+  /**
+   * Gets the raw element used to create this UiElement. The attributes of this
+   * UiElement are based on a snapshot of the raw element at construction time.
+   * If the raw element is updated later, the attributes may not match.
+   */
+  // TODO: expose in UiElement?
+  public abstract R getRawElement();
+
+  public void setUiElementActor(UiElementActor uiElementActor) {
+    this.uiElementActor = uiElementActor;
+  }
+
+  public void setValidators(Validator[] validators) {
+    this.validators = validators;
+  }
 }
diff --git a/src/com/google/android/droiddriver/base/DroidDriverContext.java b/src/com/google/android/droiddriver/base/DroidDriverContext.java
index 1c4b21f..045a0b2 100644
--- a/src/com/google/android/droiddriver/base/DroidDriverContext.java
+++ b/src/com/google/android/droiddriver/base/DroidDriverContext.java
@@ -20,11 +20,13 @@ import android.app.Instrumentation;
 import android.os.Looper;
 import android.util.Log;
 
-import com.google.android.droiddriver.actions.InputInjector;
 import com.google.android.droiddriver.exceptions.DroidDriverException;
 import com.google.android.droiddriver.exceptions.TimeoutException;
+import com.google.android.droiddriver.finders.ByXPath;
 import com.google.android.droiddriver.util.Logs;
 
+import java.util.Map;
+import java.util.WeakHashMap;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.FutureTask;
 import java.util.concurrent.TimeUnit;
@@ -32,23 +34,45 @@ import java.util.concurrent.TimeUnit;
 /**
  * Internal helper for DroidDriver implementation.
  */
-public abstract class DroidDriverContext {
+public class DroidDriverContext<R, E extends BaseUiElement<R, E>> {
   private final Instrumentation instrumentation;
+  private final BaseDroidDriver<R, E> driver;
+  private final Map<R, E> map;
 
-  protected DroidDriverContext(Instrumentation instrumentation) {
+  public DroidDriverContext(Instrumentation instrumentation, BaseDroidDriver<R, E> driver) {
     this.instrumentation = instrumentation;
+    this.driver = driver;
+    map = new WeakHashMap<R, E>();
   }
 
   public Instrumentation getInstrumentation() {
     return instrumentation;
   }
 
-  public abstract BaseDroidDriver getDriver();
+  public BaseDroidDriver<R, E> getDriver() {
+    return driver;
+  }
+
+  public E getElement(R rawElement, E parent) {
+    E element = map.get(rawElement);
+    if (element == null) {
+      element = driver.newUiElement(rawElement, parent);
+      map.put(rawElement, element);
+    }
+    return element;
+  }
 
-  public abstract InputInjector getInjector();
+  public E newRootElement(R rawRoot) {
+    clearData();
+    return getElement(rawRoot,  null /* parent */);
+  }
+
+  private void clearData() {
+    map.clear();
+    ByXPath.clearData();
+  }
 
   /** Clears UiElement instances in the context */
-  public abstract void clearData();
 
   /**
    * Tries to wait for an idle state on the main thread on best-effort basis up
diff --git a/src/com/google/android/droiddriver/finders/ByXPath.java b/src/com/google/android/droiddriver/finders/ByXPath.java
index 30cc251..946261a 100644
--- a/src/com/google/android/droiddriver/finders/ByXPath.java
+++ b/src/com/google/android/droiddriver/finders/ByXPath.java
@@ -56,10 +56,10 @@ public class ByXPath implements Finder {
   // on children they are in the same document to be appended.
   private static Document document;
   // The two maps should be kept in sync
-  private static final Map<BaseUiElement, Element> TO_DOM_MAP =
-      new HashMap<BaseUiElement, Element>();
-  private static final Map<Element, BaseUiElement> FROM_DOM_MAP =
-      new HashMap<Element, BaseUiElement>();
+  private static final Map<BaseUiElement<?, ?>, Element> TO_DOM_MAP =
+      new HashMap<BaseUiElement<?, ?>, Element>();
+  private static final Map<Element, BaseUiElement<?, ?>> FROM_DOM_MAP =
+      new HashMap<Element, BaseUiElement<?, ?>>();
 
   public static void clearData() {
     TO_DOM_MAP.clear();
@@ -86,7 +86,7 @@ public class ByXPath implements Finder {
 
   @Override
   public UiElement find(UiElement context) {
-    Element domNode = getDomNode((BaseUiElement) context, UiElement.VISIBLE);
+    Element domNode = getDomNode((BaseUiElement<?, ?>) context, UiElement.VISIBLE);
     try {
       getDocument().appendChild(domNode);
       Element foundNode = (Element) xPathExpression.evaluate(domNode, XPathConstants.NODE);
@@ -124,7 +124,8 @@ public class ByXPath implements Finder {
   /**
    * Returns the DOM node representing this UiElement.
    */
-  private static Element getDomNode(BaseUiElement uiElement, Predicate<? super UiElement> predicate) {
+  private static Element getDomNode(BaseUiElement<?, ?> uiElement,
+      Predicate<? super UiElement> predicate) {
     Element domNode = TO_DOM_MAP.get(uiElement);
     if (domNode == null) {
       domNode = buildDomNode(uiElement, predicate);
@@ -132,7 +133,7 @@ public class ByXPath implements Finder {
     return domNode;
   }
 
-  private static Element buildDomNode(BaseUiElement uiElement,
+  private static Element buildDomNode(BaseUiElement<?, ?> uiElement,
       Predicate<? super UiElement> predicate) {
     String className = uiElement.getClassName();
     if (className == null) {
@@ -175,7 +176,7 @@ public class ByXPath implements Finder {
       }
     }
 
-    for (BaseUiElement child : uiElement.getChildren(predicate)) {
+    for (BaseUiElement<?, ?> child : uiElement.getChildren(predicate)) {
       element.appendChild(getDomNode(child, predicate));
     }
     return element;
@@ -194,7 +195,7 @@ public class ByXPath implements Finder {
     }
   }
 
-  public static boolean dumpDom(String path, BaseUiElement uiElement) {
+  public static boolean dumpDom(String path, BaseUiElement<?, ?> uiElement) {
     BufferedOutputStream bos = null;
     try {
       bos = FileUtils.open(path);
diff --git a/src/com/google/android/droiddriver/instrumentation/InstrumentationContext.java b/src/com/google/android/droiddriver/instrumentation/InstrumentationContext.java
deleted file mode 100644
index 52e423a..0000000
--- a/src/com/google/android/droiddriver/instrumentation/InstrumentationContext.java
+++ /dev/null
@@ -1,80 +0,0 @@
-/*
- * Copyright (C) 2013 DroidDriver committers
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package com.google.android.droiddriver.instrumentation;
-
-import android.app.Instrumentation;
-import android.view.InputEvent;
-import android.view.KeyEvent;
-import android.view.MotionEvent;
-import android.view.View;
-
-import com.google.android.droiddriver.actions.InputInjector;
-import com.google.android.droiddriver.base.DroidDriverContext;
-import com.google.android.droiddriver.exceptions.ActionException;
-import com.google.android.droiddriver.finders.ByXPath;
-
-import java.util.Map;
-import java.util.WeakHashMap;
-
-class InstrumentationContext extends DroidDriverContext {
-  private final Map<View, ViewElement> map = new WeakHashMap<View, ViewElement>();
-  private final InstrumentationDriver driver;
-  private final InputInjector injector;
-
-  InstrumentationContext(final Instrumentation instrumentation, InstrumentationDriver driver) {
-    super(instrumentation);
-    this.driver = driver;
-    this.injector = new InputInjector() {
-      @Override
-      public boolean injectInputEvent(InputEvent event) {
-        if (event instanceof MotionEvent) {
-          instrumentation.sendPointerSync((MotionEvent) event);
-        } else if (event instanceof KeyEvent) {
-          instrumentation.sendKeySync((KeyEvent) event);
-        } else {
-          throw new ActionException("Unknown input event type: " + event);
-        }
-        return true;
-      }
-    };
-  }
-
-  @Override
-  public InstrumentationDriver getDriver() {
-    return driver;
-  }
-
-  @Override
-  public InputInjector getInjector() {
-    return injector;
-  }
-
-  ViewElement getUiElement(View view, ViewElement parent) {
-    ViewElement element = map.get(view);
-    if (element == null) {
-      element = new ViewElement(this, view, parent);
-      map.put(view, element);
-    }
-    return element;
-  }
-
-  @Override
-  public void clearData() {
-    map.clear();
-    ByXPath.clearData();
-  }
-}
diff --git a/src/com/google/android/droiddriver/instrumentation/InstrumentationDriver.java b/src/com/google/android/droiddriver/instrumentation/InstrumentationDriver.java
index adf14e2..8804211 100644
--- a/src/com/google/android/droiddriver/instrumentation/InstrumentationDriver.java
+++ b/src/com/google/android/droiddriver/instrumentation/InstrumentationDriver.java
@@ -17,16 +17,13 @@
 package com.google.android.droiddriver.instrumentation;
 
 import android.app.Instrumentation;
-import android.graphics.Bitmap;
-import android.graphics.Bitmap.Config;
-import android.graphics.Canvas;
-import android.graphics.Rect;
-import android.graphics.RectF;
 import android.os.SystemClock;
 import android.util.Log;
 import android.view.View;
 
+import com.google.android.droiddriver.actions.InputInjector;
 import com.google.android.droiddriver.base.BaseDroidDriver;
+import com.google.android.droiddriver.base.DroidDriverContext;
 import com.google.android.droiddriver.exceptions.DroidDriverException;
 import com.google.android.droiddriver.exceptions.TimeoutException;
 import com.google.android.droiddriver.util.ActivityUtils;
@@ -35,23 +32,30 @@ import com.google.android.droiddriver.util.Logs;
 /**
  * Implementation of DroidDriver that is driven via instrumentation.
  */
-public class InstrumentationDriver extends BaseDroidDriver {
-  private final InstrumentationContext context;
+public class InstrumentationDriver extends BaseDroidDriver<View, ViewElement> {
+  private final DroidDriverContext<View, ViewElement> context;
+  private final InputInjector injector;
   private final InstrumentationUiDevice uiDevice;
 
   public InstrumentationDriver(Instrumentation instrumentation) {
-    this.context = new InstrumentationContext(instrumentation, this);
+    context = new DroidDriverContext<View, ViewElement>(instrumentation, this);
+    injector = new InstrumentationInputInjector(instrumentation);
     uiDevice = new InstrumentationUiDevice(context);
   }
 
   @Override
-  protected ViewElement getNewRootElement() {
-    return context.getUiElement(findRootView(), null /* parent */);
+  public InputInjector getInjector() {
+    return injector;
   }
 
   @Override
-  protected InstrumentationContext getContext() {
-    return context;
+  protected ViewElement newRootElement() {
+    return context.newRootElement(findRootView());
+  }
+
+  @Override
+  protected ViewElement newUiElement(View rawElement, ViewElement parent) {
+    return new ViewElement(context, rawElement, parent);
   }
 
   private static class FindRootViewRunnable implements Runnable {
@@ -106,47 +110,6 @@ public class InstrumentationDriver extends BaseDroidDriver {
     }
   }
 
-  private static class ScreenshotRunnable implements Runnable {
-    private final View rootView;
-    Bitmap screenshot;
-
-    private ScreenshotRunnable(View rootView) {
-      this.rootView = rootView;
-    }
-
-    @Override
-    public void run() {
-      try {
-        rootView.destroyDrawingCache();
-        rootView.buildDrawingCache(false);
-        Bitmap drawingCache = rootView.getDrawingCache();
-        int[] xy = new int[2];
-        rootView.getLocationOnScreen(xy);
-        if (xy[0] == 0 && xy[1] == 0) {
-          screenshot = Bitmap.createBitmap(drawingCache);
-        } else {
-          Canvas canvas = new Canvas();
-          Rect rect = new Rect(0, 0, drawingCache.getWidth(), drawingCache.getHeight());
-          rect.offset(xy[0], xy[1]);
-          screenshot =
-              Bitmap.createBitmap(rect.width() + xy[0], rect.height() + xy[1], Config.ARGB_8888);
-          canvas.setBitmap(screenshot);
-          canvas.drawBitmap(drawingCache, null, new RectF(rect), null);
-          canvas.setBitmap(null);
-        }
-        rootView.destroyDrawingCache();
-      } catch (Throwable e) {
-        Logs.log(Log.ERROR, e);
-      }
-    }
-  }
-
-  Bitmap takeScreenshot() {
-    ScreenshotRunnable screenshotRunnable = new ScreenshotRunnable(findRootView());
-    context.runOnMainSync(screenshotRunnable);
-    return screenshotRunnable.screenshot;
-  }
-
   @Override
   public InstrumentationUiDevice getUiDevice() {
     return uiDevice;
diff --git a/src/com/google/android/droiddriver/instrumentation/InstrumentationInputInjector.java b/src/com/google/android/droiddriver/instrumentation/InstrumentationInputInjector.java
new file mode 100644
index 0000000..7e47e90
--- /dev/null
+++ b/src/com/google/android/droiddriver/instrumentation/InstrumentationInputInjector.java
@@ -0,0 +1,45 @@
+/*
+ * Copyright (C) 2013 DroidDriver committers
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.android.droiddriver.instrumentation;
+
+import android.app.Instrumentation;
+import android.view.InputEvent;
+import android.view.KeyEvent;
+import android.view.MotionEvent;
+
+import com.google.android.droiddriver.actions.InputInjector;
+import com.google.android.droiddriver.exceptions.ActionException;
+
+public class InstrumentationInputInjector implements InputInjector {
+  private final Instrumentation instrumentation;
+
+  public InstrumentationInputInjector(Instrumentation instrumentation) {
+    this.instrumentation = instrumentation;
+  }
+
+  @Override
+  public boolean injectInputEvent(InputEvent event) {
+    if (event instanceof MotionEvent) {
+      instrumentation.sendPointerSync((MotionEvent) event);
+    } else if (event instanceof KeyEvent) {
+      instrumentation.sendKeySync((KeyEvent) event);
+    } else {
+      throw new ActionException("Unknown input event type: " + event);
+    }
+    return true;
+  }
+}
diff --git a/src/com/google/android/droiddriver/instrumentation/InstrumentationUiDevice.java b/src/com/google/android/droiddriver/instrumentation/InstrumentationUiDevice.java
index a415918..f94137f 100644
--- a/src/com/google/android/droiddriver/instrumentation/InstrumentationUiDevice.java
+++ b/src/com/google/android/droiddriver/instrumentation/InstrumentationUiDevice.java
@@ -17,23 +17,69 @@
 package com.google.android.droiddriver.instrumentation;
 
 import android.graphics.Bitmap;
+import android.graphics.Canvas;
+import android.graphics.Rect;
+import android.graphics.RectF;
+import android.graphics.Bitmap.Config;
+import android.util.Log;
+import android.view.View;
 
 import com.google.android.droiddriver.base.BaseUiDevice;
+import com.google.android.droiddriver.base.DroidDriverContext;
+import com.google.android.droiddriver.util.Logs;
 
 class InstrumentationUiDevice extends BaseUiDevice {
-  private final InstrumentationContext context;
+  private final DroidDriverContext<View, ViewElement> context;
 
-  InstrumentationUiDevice(InstrumentationContext context) {
+  InstrumentationUiDevice(DroidDriverContext<View, ViewElement> context) {
     this.context = context;
   }
 
   @Override
   protected Bitmap takeScreenshot() {
-    return context.getDriver().takeScreenshot();
+    ScreenshotRunnable screenshotRunnable =
+        new ScreenshotRunnable(context.getDriver().getRootElement().getRawElement());
+    context.runOnMainSync(screenshotRunnable);
+    return screenshotRunnable.screenshot;
   }
 
   @Override
-  protected InstrumentationContext getContext() {
+  protected DroidDriverContext<View, ViewElement> getContext() {
     return context;
   }
+
+  private static class ScreenshotRunnable implements Runnable {
+    private final View rootView;
+    Bitmap screenshot;
+
+    private ScreenshotRunnable(View rootView) {
+      this.rootView = rootView;
+    }
+
+    @Override
+    public void run() {
+      try {
+        rootView.destroyDrawingCache();
+        rootView.buildDrawingCache(false);
+        Bitmap drawingCache = rootView.getDrawingCache();
+        int[] xy = new int[2];
+        rootView.getLocationOnScreen(xy);
+        if (xy[0] == 0 && xy[1] == 0) {
+          screenshot = Bitmap.createBitmap(drawingCache);
+        } else {
+          Canvas canvas = new Canvas();
+          Rect rect = new Rect(0, 0, drawingCache.getWidth(), drawingCache.getHeight());
+          rect.offset(xy[0], xy[1]);
+          screenshot =
+              Bitmap.createBitmap(rect.width() + xy[0], rect.height() + xy[1], Config.ARGB_8888);
+          canvas.setBitmap(screenshot);
+          canvas.drawBitmap(drawingCache, null, new RectF(rect), null);
+          canvas.setBitmap(null);
+        }
+        rootView.destroyDrawingCache();
+      } catch (Throwable e) {
+        Logs.log(Log.ERROR, e);
+      }
+    }
+  }
 }
diff --git a/src/com/google/android/droiddriver/instrumentation/ViewElement.java b/src/com/google/android/droiddriver/instrumentation/ViewElement.java
index fd4c39a..d1379cd 100644
--- a/src/com/google/android/droiddriver/instrumentation/ViewElement.java
+++ b/src/com/google/android/droiddriver/instrumentation/ViewElement.java
@@ -26,9 +26,9 @@ import android.view.accessibility.AccessibilityNodeInfo;
 import android.widget.Checkable;
 import android.widget.TextView;
 
-import com.google.android.droiddriver.actions.EventUiElementActor;
 import com.google.android.droiddriver.actions.InputInjector;
 import com.google.android.droiddriver.base.BaseUiElement;
+import com.google.android.droiddriver.base.DroidDriverContext;
 import com.google.android.droiddriver.exceptions.DroidDriverException;
 import com.google.android.droiddriver.finders.Attribute;
 import com.google.android.droiddriver.util.Preconditions;
@@ -44,7 +44,7 @@ import java.util.concurrent.FutureTask;
 /**
  * A UiElement that is backed by a View.
  */
-public class ViewElement extends BaseUiElement {
+public class ViewElement extends BaseUiElement<View, ViewElement> {
   private static class SnapshotViewAttributesRunnable implements Runnable {
     private final View view;
     final Map<Attribute, Object> attribs = new EnumMap<Attribute, Object>(Attribute.class);
@@ -205,7 +205,8 @@ public class ViewElement extends BaseUiElement {
     CLASS_NAME_OVERRIDES.put(actualClassName, overridingClassName);
   }
 
-  private final InstrumentationContext context;
+  private final DroidDriverContext<View, ViewElement> context;
+  private final View view;
   private final Map<Attribute, Object> attributes;
   private final boolean visible;
   private final Rect visibleBounds;
@@ -218,10 +219,9 @@ public class ViewElement extends BaseUiElement {
    * updated, a new {@code ViewElement} instance will be created in
    * {@link com.google.android.droiddriver.DroidDriver#refreshUiElementTree}.
    */
-  public ViewElement(final InstrumentationContext context, View view, ViewElement parent) {
-    super(EventUiElementActor.INSTANCE);
+  public ViewElement(DroidDriverContext<View, ViewElement> context, View view, ViewElement parent) {
     this.context = Preconditions.checkNotNull(context);
-    Preconditions.checkNotNull(view);
+    this.view = Preconditions.checkNotNull(view);
     this.parent = parent;
     SnapshotViewAttributesRunnable attributesSnapshot = new SnapshotViewAttributesRunnable(view);
     context.runOnMainSync(attributesSnapshot);
@@ -237,7 +237,7 @@ public class ViewElement extends BaseUiElement {
     } else {
       List<ViewElement> children = new ArrayList<ViewElement>(attributesSnapshot.childViews.size());
       for (View childView : attributesSnapshot.childViews) {
-        children.add(context.getUiElement(childView, this));
+        children.add(context.getElement(childView, this));
       }
       this.children = Collections.unmodifiableList(children);
     }
@@ -270,7 +270,7 @@ public class ViewElement extends BaseUiElement {
 
   @Override
   public InputInjector getInjector() {
-    return context.getInjector();
+    return context.getDriver().getInjector();
   }
 
   @Override
@@ -278,4 +278,9 @@ public class ViewElement extends BaseUiElement {
     futureTask.run();
     context.tryWaitForIdleSync(timeoutMillis);
   }
+
+  @Override
+  public View getRawElement() {
+    return view;
+  }
 }
diff --git a/src/com/google/android/droiddriver/scroll/AccessibilityEventScrollStepStrategy.java b/src/com/google/android/droiddriver/scroll/AccessibilityEventScrollStepStrategy.java
index 6911fa6..fee4e2b 100644
--- a/src/com/google/android/droiddriver/scroll/AccessibilityEventScrollStepStrategy.java
+++ b/src/com/google/android/droiddriver/scroll/AccessibilityEventScrollStepStrategy.java
@@ -159,7 +159,7 @@ public class AccessibilityEventScrollStepStrategy implements ScrollStepStrategy
 
   @Override
   public String toString() {
-    return String.format("AccessibilityEventScrollStepStrategy{scrollEventTimeoutMillis=%d}",
+    return String.format("%s{scrollEventTimeoutMillis=%d}", getClass().getSimpleName(),
         scrollEventTimeoutMillis);
   }
 
@@ -194,9 +194,10 @@ public class AccessibilityEventScrollStepStrategy implements ScrollStepStrategy
 
   @Override
   public void doScroll(final UiElement container, final PhysicalDirection direction) {
-    // We do not call container.scroll(direction) because container.scroll internally calls
-    // UiAutomation.executeAndWaitForEvent which clears the AccessibilityEvent Queue, preventing us
-    // from fetching the last accessibility event to determine if scrolling has finished.
+    // We do not call container.scroll(direction) because container.scroll
+    // internally calls UiAutomation.executeAndWaitForEvent which clears the
+    // AccessibilityEvent Queue, preventing us from fetching the last
+    // accessibility event to determine if scrolling has finished.
     SwipeAction.toScroll(direction).perform(container);
   }
 
diff --git a/src/com/google/android/droiddriver/uiautomation/accessibility/AccessibilityDriver.java b/src/com/google/android/droiddriver/uiautomation/AccessibilityDriver.java
index 2f2295c..63f6a59 100644
--- a/src/com/google/android/droiddriver/uiautomation/accessibility/AccessibilityDriver.java
+++ b/src/com/google/android/droiddriver/uiautomation/AccessibilityDriver.java
@@ -14,23 +14,29 @@
  * limitations under the License.
  */
 
-package com.google.android.droiddriver.uiautomation.accessibility;
+package com.google.android.droiddriver.uiautomation;
 
 import android.app.Instrumentation;
+import android.view.accessibility.AccessibilityNodeInfo;
 
-import com.google.android.droiddriver.uiautomation.base.BaseUiAutomationDriver;
+import com.google.android.droiddriver.validators.DefaultAccessibilityValidator;
+import com.google.android.droiddriver.validators.Validator;
 
 /**
- * Implementation of DroidDriver that gets attributes via the Accessibility API
- * and is acted upon via the Accessibility API.
+ * A UiAutomationDriver that validates accessibility.
  */
-public class AccessibilityDriver extends BaseUiAutomationDriver<AccessibilityElement> {
+public class AccessibilityDriver extends UiAutomationDriver {
+  private static final Validator[] VALIDATORS = {new DefaultAccessibilityValidator()};
+
   public AccessibilityDriver(Instrumentation instrumentation) {
     super(instrumentation);
   }
 
   @Override
-  protected AccessibilityContext newContext(Instrumentation instrumentation) {
-    return new AccessibilityContext(instrumentation, this);
+  protected UiAutomationElement newUiElement(AccessibilityNodeInfo rawElement,
+      UiAutomationElement parent) {
+    UiAutomationElement newUiElement = super.newUiElement(rawElement, parent);
+    newUiElement.setValidators(VALIDATORS);
+    return newUiElement;
   }
 }
diff --git a/src/com/google/android/droiddriver/uiautomation/UiAutomationContext.java b/src/com/google/android/droiddriver/uiautomation/UiAutomationContext.java
index 04df113..2cdcedf 100644
--- a/src/com/google/android/droiddriver/uiautomation/UiAutomationContext.java
+++ b/src/com/google/android/droiddriver/uiautomation/UiAutomationContext.java
@@ -17,17 +17,40 @@
 package com.google.android.droiddriver.uiautomation;
 
 import android.app.Instrumentation;
+import android.app.UiAutomation;
 import android.view.accessibility.AccessibilityNodeInfo;
 
-import com.google.android.droiddriver.uiautomation.base.BaseUiAutomationContext;
+import com.google.android.droiddriver.base.DroidDriverContext;
+import com.google.android.droiddriver.exceptions.UnrecoverableException;
 
-class UiAutomationContext extends BaseUiAutomationContext<UiAutomationElement> {
-  UiAutomationContext(Instrumentation instrumentation, UiAutomationDriver driver) {
+public class UiAutomationContext extends
+    DroidDriverContext<AccessibilityNodeInfo, UiAutomationElement> {
+  private final UiAutomation uiAutomation;
+
+  protected UiAutomationContext(Instrumentation instrumentation, UiAutomationDriver driver) {
     super(instrumentation, driver);
+    this.uiAutomation = instrumentation.getUiAutomation();
   }
 
   @Override
-  protected UiAutomationElement newUiElement(AccessibilityNodeInfo node, UiAutomationElement parent) {
-    return new UiAutomationElement(this, node, parent);
+  public UiAutomationDriver getDriver() {
+    return (UiAutomationDriver) super.getDriver();
+  }
+
+  public interface UiAutomationCallable<T> {
+    T call(UiAutomation uiAutomation);
+  }
+
+  /**
+   * Wraps calls to UiAutomation API. Currently supports fail-fast if
+   * UiAutomation throws IllegalStateException, which occurs when the connection
+   * to UiAutomation service is lost.
+   */
+  public <T> T callUiAutomation(UiAutomationCallable<T> uiAutomationCallable) {
+    try {
+      return uiAutomationCallable.call(uiAutomation);
+    } catch (IllegalStateException e) {
+      throw new UnrecoverableException(e);
+    }
   }
 }
diff --git a/src/com/google/android/droiddriver/uiautomation/UiAutomationDriver.java b/src/com/google/android/droiddriver/uiautomation/UiAutomationDriver.java
index 9291f13..f84ab5f 100644
--- a/src/com/google/android/droiddriver/uiautomation/UiAutomationDriver.java
+++ b/src/com/google/android/droiddriver/uiautomation/UiAutomationDriver.java
@@ -17,20 +17,122 @@
 package com.google.android.droiddriver.uiautomation;
 
 import android.app.Instrumentation;
+import android.app.UiAutomation;
+import android.content.Context;
+import android.os.SystemClock;
+import android.view.accessibility.AccessibilityEvent;
+import android.view.accessibility.AccessibilityManager;
+import android.view.accessibility.AccessibilityNodeInfo;
 
-import com.google.android.droiddriver.uiautomation.base.BaseUiAutomationDriver;
+import com.google.android.droiddriver.actions.InputInjector;
+import com.google.android.droiddriver.base.BaseDroidDriver;
+import com.google.android.droiddriver.exceptions.TimeoutException;
+import com.google.android.droiddriver.uiautomation.UiAutomationContext.UiAutomationCallable;
+import com.google.android.droiddriver.util.Logs;
 
 /**
  * Implementation of DroidDriver that gets attributes via the Accessibility API
  * and is acted upon via synthesized events.
  */
-public class UiAutomationDriver extends BaseUiAutomationDriver<UiAutomationElement> {
+public class UiAutomationDriver extends BaseDroidDriver<AccessibilityNodeInfo, UiAutomationElement> {
+  // TODO: magic const from UiAutomator, but may not be useful
+  /**
+   * This value has the greatest bearing on the appearance of test execution
+   * speeds. This value is used as the minimum time to wait before considering
+   * the UI idle after each action.
+   */
+  private static final long QUIET_TIME_TO_BE_CONSIDERD_IDLE_STATE = 500;// ms
+
+  private final UiAutomationContext context;
+  private final InputInjector injector;
+  private final UiAutomationUiDevice uiDevice;
+
   public UiAutomationDriver(Instrumentation instrumentation) {
-    super(instrumentation);
+    context = new UiAutomationContext(instrumentation, this);
+    injector = new UiAutomationInputInjector(context);
+    uiDevice = new UiAutomationUiDevice(context);
+  }
+
+  @Override
+  public InputInjector getInjector() {
+    return injector;
+  }
+
+  @Override
+  protected UiAutomationElement newRootElement() {
+    return context.newRootElement(getRootNode());
+  }
+
+  @Override
+  protected UiAutomationElement newUiElement(AccessibilityNodeInfo rawElement,
+      UiAutomationElement parent) {
+    return new UiAutomationElement(context, rawElement, parent);
+  }
+
+  private AccessibilityNodeInfo getRootNode() {
+    final long timeoutMillis = getPoller().getTimeoutMillis();
+    context.callUiAutomation(new UiAutomationCallable<Void>() {
+      @Override
+      public Void call(UiAutomation uiAutomation) {
+        try {
+          uiAutomation.waitForIdle(QUIET_TIME_TO_BE_CONSIDERD_IDLE_STATE, timeoutMillis);
+          return null;
+        } catch (java.util.concurrent.TimeoutException e) {
+          throw new TimeoutException(e);
+        }
+      }
+    });
+
+    long end = SystemClock.uptimeMillis() + timeoutMillis;
+    while (true) {
+      AccessibilityNodeInfo root =
+          context.callUiAutomation(new UiAutomationCallable<AccessibilityNodeInfo>() {
+            @Override
+            public AccessibilityNodeInfo call(UiAutomation uiAutomation) {
+              return uiAutomation.getRootInActiveWindow();
+            }
+          });
+      if (root != null) {
+        return root;
+      }
+      long remainingMillis = end - SystemClock.uptimeMillis();
+      if (remainingMillis < 0) {
+        throw new TimeoutException(
+            String.format("Timed out after %d milliseconds waiting for root AccessibilityNodeInfo",
+                timeoutMillis));
+      }
+      SystemClock.sleep(Math.min(250, remainingMillis));
+    }
+  }
+
+  /**
+   * Some widgets fail to trigger some AccessibilityEvent's after actions,
+   * resulting in stale AccessibilityNodeInfo's. As a work-around, force to
+   * clear the AccessibilityNodeInfoCache.
+   */
+  public void clearAccessibilityNodeInfoCache() {
+    Logs.call(this, "clearAccessibilityNodeInfoCache");
+    uiDevice.sleep();
+    uiDevice.wakeUp();
+  }
+
+  /**
+   * {@link #clearAccessibilityNodeInfoCache} causes the screen to blink. This
+   * method clears the cache without blinking by employing an implementation
+   * detail of AccessibilityNodeInfoCache. This is a hack; use it at your own
+   * discretion.
+   */
+  public void clearAccessibilityNodeInfoCacheHack() {
+    Logs.call(this, "clearAccessibilityNodeInfoCacheHack");
+    AccessibilityManager accessibilityManager =
+        (AccessibilityManager) context.getInstrumentation().getTargetContext()
+            .getSystemService(Context.ACCESSIBILITY_SERVICE);
+    accessibilityManager.sendAccessibilityEvent(AccessibilityEvent
+        .obtain(AccessibilityEvent.TYPE_WINDOW_STATE_CHANGED));
   }
 
   @Override
-  protected UiAutomationContext newContext(Instrumentation instrumentation) {
-    return new UiAutomationContext(instrumentation, this);
+  public UiAutomationUiDevice getUiDevice() {
+    return uiDevice;
   }
 }
diff --git a/src/com/google/android/droiddriver/uiautomation/UiAutomationElement.java b/src/com/google/android/droiddriver/uiautomation/UiAutomationElement.java
index 9a4309b..3fa8653 100644
--- a/src/com/google/android/droiddriver/uiautomation/UiAutomationElement.java
+++ b/src/com/google/android/droiddriver/uiautomation/UiAutomationElement.java
@@ -16,17 +16,198 @@
 
 package com.google.android.droiddriver.uiautomation;
 
+import static com.google.android.droiddriver.util.Strings.charSequenceToString;
+
+import android.app.UiAutomation;
+import android.app.UiAutomation.AccessibilityEventFilter;
+import android.graphics.Rect;
+import android.view.accessibility.AccessibilityEvent;
 import android.view.accessibility.AccessibilityNodeInfo;
 
-import com.google.android.droiddriver.actions.EventUiElementActor;
-import com.google.android.droiddriver.uiautomation.base.BaseUiAutomationElement;
+import com.google.android.droiddriver.actions.InputInjector;
+import com.google.android.droiddriver.base.BaseUiElement;
+import com.google.android.droiddriver.finders.Attribute;
+import com.google.android.droiddriver.uiautomation.UiAutomationContext.UiAutomationCallable;
+import com.google.android.droiddriver.util.Preconditions;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.EnumMap;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.FutureTask;
+import java.util.concurrent.TimeoutException;
 
 /**
- * A BaseUiAutomationElement that is acted upon via synthesized events.
+ * A UiElement that gets attributes via the Accessibility API.
  */
-class UiAutomationElement extends BaseUiAutomationElement<UiAutomationElement> {
-  UiAutomationElement(UiAutomationContext context, AccessibilityNodeInfo node,
+public class UiAutomationElement extends BaseUiElement<AccessibilityNodeInfo, UiAutomationElement> {
+  private static final AccessibilityEventFilter ANY_EVENT_FILTER = new AccessibilityEventFilter() {
+    @Override
+    public boolean accept(AccessibilityEvent arg0) {
+      return true;
+    }
+  };
+
+  private final AccessibilityNodeInfo node;
+  private final UiAutomationContext context;
+  private final Map<Attribute, Object> attributes;
+  private final boolean visible;
+  private final Rect visibleBounds;
+  private final UiAutomationElement parent;
+  private final List<UiAutomationElement> children;
+
+  /**
+   * A snapshot of all attributes is taken at construction. The attributes of a
+   * {@code UiAutomationElement} instance are immutable. If the underlying
+   * {@link AccessibilityNodeInfo} is updated, a new {@code UiAutomationElement}
+   * instance will be created in
+   * {@link com.google.android.droiddriver.DroidDriver#refreshUiElementTree}.
+   */
+  protected UiAutomationElement(UiAutomationContext context, AccessibilityNodeInfo node,
       UiAutomationElement parent) {
-    super(context, node, parent, EventUiElementActor.INSTANCE);
+    this.node = Preconditions.checkNotNull(node);
+    this.context = Preconditions.checkNotNull(context);
+    this.parent = parent;
+
+    Map<Attribute, Object> attribs = new EnumMap<Attribute, Object>(Attribute.class);
+    put(attribs, Attribute.PACKAGE, charSequenceToString(node.getPackageName()));
+    put(attribs, Attribute.CLASS, charSequenceToString(node.getClassName()));
+    put(attribs, Attribute.TEXT, charSequenceToString(node.getText()));
+    put(attribs, Attribute.CONTENT_DESC, charSequenceToString(node.getContentDescription()));
+    put(attribs, Attribute.RESOURCE_ID, charSequenceToString(node.getViewIdResourceName()));
+    put(attribs, Attribute.CHECKABLE, node.isCheckable());
+    put(attribs, Attribute.CHECKED, node.isChecked());
+    put(attribs, Attribute.CLICKABLE, node.isClickable());
+    put(attribs, Attribute.ENABLED, node.isEnabled());
+    put(attribs, Attribute.FOCUSABLE, node.isFocusable());
+    put(attribs, Attribute.FOCUSED, node.isFocused());
+    put(attribs, Attribute.LONG_CLICKABLE, node.isLongClickable());
+    put(attribs, Attribute.PASSWORD, node.isPassword());
+    put(attribs, Attribute.SCROLLABLE, node.isScrollable());
+    if (node.getTextSelectionStart() >= 0
+        && node.getTextSelectionStart() != node.getTextSelectionEnd()) {
+      attribs.put(Attribute.SELECTION_START, node.getTextSelectionStart());
+      attribs.put(Attribute.SELECTION_END, node.getTextSelectionEnd());
+    }
+    put(attribs, Attribute.SELECTED, node.isSelected());
+    put(attribs, Attribute.BOUNDS, getBounds(node));
+    attributes = Collections.unmodifiableMap(attribs);
+
+    // Order matters as getVisibleBounds depends on visible
+    visible = node.isVisibleToUser();
+    visibleBounds = getVisibleBounds(node);
+    List<UiAutomationElement> mutableChildren = buildChildren(node);
+    this.children = mutableChildren == null ? null : Collections.unmodifiableList(mutableChildren);
+  }
+
+  private void put(Map<Attribute, Object> attribs, Attribute key, Object value) {
+    if (value != null) {
+      attribs.put(key, value);
+    }
+  }
+
+  private List<UiAutomationElement> buildChildren(AccessibilityNodeInfo node) {
+    List<UiAutomationElement> children;
+    int childCount = node.getChildCount();
+    if (childCount == 0) {
+      children = null;
+    } else {
+      children = new ArrayList<UiAutomationElement>(childCount);
+      for (int i = 0; i < childCount; i++) {
+        AccessibilityNodeInfo child = node.getChild(i);
+        if (child != null) {
+          children.add(context.getElement(child, this));
+        }
+      }
+    }
+    return children;
+  }
+
+  private Rect getBounds(AccessibilityNodeInfo node) {
+    Rect rect = new Rect();
+    node.getBoundsInScreen(rect);
+    return rect;
+  }
+
+  private Rect getVisibleBounds(AccessibilityNodeInfo node) {
+    if (!visible) {
+      return new Rect();
+    }
+    Rect visibleBounds = getBounds();
+    UiAutomationElement parent = getParent();
+    Rect parentBounds;
+    while (parent != null) {
+      parentBounds = parent.getBounds();
+      visibleBounds.intersect(parentBounds);
+      parent = parent.getParent();
+    }
+    return visibleBounds;
+  }
+
+  @Override
+  public Rect getVisibleBounds() {
+    return visibleBounds;
+  }
+
+  @Override
+  public boolean isVisible() {
+    return visible;
+  }
+
+  @Override
+  public UiAutomationElement getParent() {
+    return parent;
+  }
+
+  @Override
+  protected List<UiAutomationElement> getChildren() {
+    return children;
+  }
+
+  @Override
+  protected Map<Attribute, Object> getAttributes() {
+    return attributes;
+  }
+
+  @Override
+  public InputInjector getInjector() {
+    return context.getDriver().getInjector();
+  }
+
+  /**
+   * Note: This implementation of {@code doPerformAndWait} clears the
+   * {@code AccessibilityEvent} queue.
+   */
+  @Override
+  protected void doPerformAndWait(final FutureTask<Boolean> futureTask, final long timeoutMillis) {
+    context.callUiAutomation(new UiAutomationCallable<Void>() {
+
+      @Override
+      public Void call(UiAutomation uiAutomation) {
+        try {
+          uiAutomation.executeAndWaitForEvent(futureTask, ANY_EVENT_FILTER, timeoutMillis);
+        } catch (TimeoutException e) {
+          // This is for sync'ing with Accessibility API on best-effort because
+          // it is not reliable.
+          // Exception is ignored here. Tests will fail anyways if this is
+          // critical.
+          // Actions should usually trigger some AccessibilityEvent's, but some
+          // widgets fail to do so, resulting in stale AccessibilityNodeInfo's.
+          // As a work-around, force to clear the AccessibilityNodeInfoCache.
+          // A legitimate case of no AccessibilityEvent is when scrolling has
+          // reached the end, but we cannot tell whether it's legitimate or the
+          // widget has bugs, so clearAccessibilityNodeInfoCache anyways.
+          context.getDriver().clearAccessibilityNodeInfoCacheHack();
+        }
+        return null;
+      }
+
+    });
+  }
+
+  @Override
+  public AccessibilityNodeInfo getRawElement() {
+    return node;
   }
 }
diff --git a/src/com/google/android/droiddriver/uiautomation/base/UiAutomationInputInjector.java b/src/com/google/android/droiddriver/uiautomation/UiAutomationInputInjector.java
index 5d13d2d..94d3ab4 100644
--- a/src/com/google/android/droiddriver/uiautomation/base/UiAutomationInputInjector.java
+++ b/src/com/google/android/droiddriver/uiautomation/UiAutomationInputInjector.java
@@ -14,17 +14,18 @@
  * limitations under the License.
  */
 
-package com.google.android.droiddriver.uiautomation.base;
+package com.google.android.droiddriver.uiautomation;
 
 import android.app.UiAutomation;
 import android.view.InputEvent;
 
 import com.google.android.droiddriver.actions.InputInjector;
+import com.google.android.droiddriver.uiautomation.UiAutomationContext.UiAutomationCallable;
 
 public class UiAutomationInputInjector implements InputInjector {
-  private final BaseUiAutomationContext<?> context;
+  private final UiAutomationContext context;
 
-  public UiAutomationInputInjector(BaseUiAutomationContext<?> context) {
+  public UiAutomationInputInjector(UiAutomationContext context) {
     this.context = context;
   }
 
diff --git a/src/com/google/android/droiddriver/uiautomation/base/UiAutomationUiDevice.java b/src/com/google/android/droiddriver/uiautomation/UiAutomationUiDevice.java
index 5c66ef5..a376cb6 100644
--- a/src/com/google/android/droiddriver/uiautomation/base/UiAutomationUiDevice.java
+++ b/src/com/google/android/droiddriver/uiautomation/UiAutomationUiDevice.java
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package com.google.android.droiddriver.uiautomation.base;
+package com.google.android.droiddriver.uiautomation;
 
 import android.app.UiAutomation;
 import android.graphics.Bitmap;
@@ -22,12 +22,13 @@ import android.util.Log;
 
 import com.google.android.droiddriver.base.BaseUiDevice;
 import com.google.android.droiddriver.exceptions.UnrecoverableException;
+import com.google.android.droiddriver.uiautomation.UiAutomationContext.UiAutomationCallable;
 import com.google.android.droiddriver.util.Logs;
 
 class UiAutomationUiDevice extends BaseUiDevice {
-  private final BaseUiAutomationContext<?> context;
+  private final UiAutomationContext context;
 
-  UiAutomationUiDevice(BaseUiAutomationContext<?> context) {
+  UiAutomationUiDevice(UiAutomationContext context) {
     this.context = context;
   }
 
@@ -49,7 +50,7 @@ class UiAutomationUiDevice extends BaseUiDevice {
   }
 
   @Override
-  protected BaseUiAutomationContext<?> getContext() {
+  protected UiAutomationContext getContext() {
     return context;
   }
 }
diff --git a/src/com/google/android/droiddriver/uiautomation/accessibility/AccessibilityContext.java b/src/com/google/android/droiddriver/uiautomation/accessibility/AccessibilityContext.java
deleted file mode 100644
index 4c76d29..0000000
--- a/src/com/google/android/droiddriver/uiautomation/accessibility/AccessibilityContext.java
+++ /dev/null
@@ -1,53 +0,0 @@
-/*
- * Copyright (C) 2013 DroidDriver committers
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package com.google.android.droiddriver.uiautomation.accessibility;
-
-import android.app.Instrumentation;
-import android.view.InputEvent;
-import android.view.MotionEvent;
-import android.view.accessibility.AccessibilityNodeInfo;
-
-import com.google.android.droiddriver.actions.InputInjector;
-import com.google.android.droiddriver.exceptions.DroidDriverException;
-import com.google.android.droiddriver.uiautomation.base.BaseUiAutomationContext;
-import com.google.android.droiddriver.uiautomation.base.UiAutomationInputInjector;
-
-class AccessibilityContext extends BaseUiAutomationContext<AccessibilityElement> {
-  AccessibilityContext(Instrumentation instrumentation, AccessibilityDriver driver) {
-    super(instrumentation, driver);
-  }
-
-  @Override
-  protected InputInjector newInputInjector() {
-    return new UiAutomationInputInjector(this) {
-      @Override
-      public boolean injectInputEvent(InputEvent event) {
-        if (event instanceof MotionEvent) {
-          throw new DroidDriverException(
-              "AccessibilityDriver forbids MotionEvent in order to detect accessibility issues");
-        }
-        return super.injectInputEvent(event);
-      }
-    };
-  }
-
-  @Override
-  protected AccessibilityElement newUiElement(AccessibilityNodeInfo node,
-      AccessibilityElement parent) {
-    return new AccessibilityElement(this, node, parent);
-  }
-}
diff --git a/src/com/google/android/droiddriver/uiautomation/accessibility/AccessibilityElement.java b/src/com/google/android/droiddriver/uiautomation/accessibility/AccessibilityElement.java
deleted file mode 100644
index c208730..0000000
--- a/src/com/google/android/droiddriver/uiautomation/accessibility/AccessibilityElement.java
+++ /dev/null
@@ -1,51 +0,0 @@
-/*
- * Copyright (C) 2013 DroidDriver committers
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package com.google.android.droiddriver.uiautomation.accessibility;
-
-import android.text.TextUtils;
-import android.view.accessibility.AccessibilityNodeInfo;
-
-import com.google.android.droiddriver.actions.Action;
-import com.google.android.droiddriver.actions.accessibility.AccessibilityUiElementActor;
-import com.google.android.droiddriver.exceptions.DroidDriverException;
-import com.google.android.droiddriver.uiautomation.base.BaseUiAutomationElement;
-
-/**
- * A UiElement that gets attributes via the Accessibility API and is acted upon
- * via the Accessibility API.
- */
-class AccessibilityElement extends BaseUiAutomationElement<AccessibilityElement> {
-  AccessibilityElement(AccessibilityContext context, AccessibilityNodeInfo node,
-      AccessibilityElement parent) {
-    super(context, node, parent, AccessibilityUiElementActor.INSTANCE);
-  }
-
-  @Override
-  public boolean perform(Action action) {
-    checkAccessible();
-    return super.perform(action);
-  }
-
-  private void checkAccessible() {
-    if (getParent() != null // don't check root
-        && TextUtils.isEmpty(this.getContentDescription()) && TextUtils.isEmpty(this.getText())) {
-      throw new DroidDriverException(
-          "Accessibility issue: either content description or text must be set for actionable"
-              + " user interface controls");
-    }
-  }
-}
diff --git a/src/com/google/android/droiddriver/uiautomation/base/BaseUiAutomationContext.java b/src/com/google/android/droiddriver/uiautomation/base/BaseUiAutomationContext.java
deleted file mode 100644
index 1412818..0000000
--- a/src/com/google/android/droiddriver/uiautomation/base/BaseUiAutomationContext.java
+++ /dev/null
@@ -1,97 +0,0 @@
-/*
- * Copyright (C) 2013 DroidDriver committers
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package com.google.android.droiddriver.uiautomation.base;
-
-import android.app.Instrumentation;
-import android.app.UiAutomation;
-import android.view.accessibility.AccessibilityNodeInfo;
-
-import com.google.android.droiddriver.actions.InputInjector;
-import com.google.android.droiddriver.base.DroidDriverContext;
-import com.google.android.droiddriver.exceptions.UnrecoverableException;
-import com.google.android.droiddriver.finders.ByXPath;
-
-import java.util.Map;
-import java.util.WeakHashMap;
-
-public abstract class BaseUiAutomationContext<E extends BaseUiAutomationElement<E>> extends
-    DroidDriverContext {
-  private final UiAutomation uiAutomation;
-  private final BaseUiAutomationDriver<E> driver;
-  private final InputInjector injector;
-  private final Map<AccessibilityNodeInfo, E> map;
-
-  protected BaseUiAutomationContext(Instrumentation instrumentation,
-      BaseUiAutomationDriver<E> driver) {
-    super(instrumentation);
-    this.uiAutomation = instrumentation.getUiAutomation();
-    this.driver = driver;
-    this.map = new WeakHashMap<AccessibilityNodeInfo, E>();
-    injector = newInputInjector();
-  }
-
-  /**
-   * Subclasses can override to return a different InputInjector, for example,
-   * forbidding MotionEvent in order to detect accessibility issues.
-   */
-  protected InputInjector newInputInjector() {
-    return new UiAutomationInputInjector(this);
-  }
-
-  /**
-   * Returns a new UiElement of type {@code E}.
-   */
-  protected abstract E newUiElement(AccessibilityNodeInfo node, E parent);
-
-  @Override
-  public BaseUiAutomationDriver<E> getDriver() {
-    return driver;
-  }
-
-  @Override
-  public InputInjector getInjector() {
-    return injector;
-  }
-
-  E getUiElement(AccessibilityNodeInfo node, E parent) {
-    E element = map.get(node);
-    if (element == null) {
-      element = newUiElement(node, parent);
-      map.put(node, element);
-    }
-    return element;
-  }
-
-  @Override
-  public void clearData() {
-    map.clear();
-    ByXPath.clearData();
-  }
-
-  /**
-   * Wraps calls to UiAutomation API. Currently supports fail-fast if
-   * UiAutomation throws IllegalStateException, which occurs when the connection
-   * to UiAutomation service is lost.
-   */
-  public <T> T callUiAutomation(UiAutomationCallable<T> uiAutomationCallable) {
-    try {
-      return uiAutomationCallable.call(uiAutomation);
-    } catch (IllegalStateException e) {
-      throw new UnrecoverableException(e);
-    }
-  }
-}
diff --git a/src/com/google/android/droiddriver/uiautomation/base/BaseUiAutomationDriver.java b/src/com/google/android/droiddriver/uiautomation/base/BaseUiAutomationDriver.java
deleted file mode 100644
index fe223e3..0000000
--- a/src/com/google/android/droiddriver/uiautomation/base/BaseUiAutomationDriver.java
+++ /dev/null
@@ -1,131 +0,0 @@
-/*
- * Copyright (C) 2013 DroidDriver committers
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package com.google.android.droiddriver.uiautomation.base;
-
-import android.app.Instrumentation;
-import android.app.UiAutomation;
-import android.content.Context;
-import android.os.SystemClock;
-import android.view.accessibility.AccessibilityEvent;
-import android.view.accessibility.AccessibilityManager;
-import android.view.accessibility.AccessibilityNodeInfo;
-
-import com.google.android.droiddriver.base.BaseDroidDriver;
-import com.google.android.droiddriver.exceptions.TimeoutException;
-import com.google.android.droiddriver.util.Logs;
-
-/**
- * Base implementation of DroidDriver that gets attributes via the Accessibility
- * API.
- */
-public abstract class BaseUiAutomationDriver<E extends BaseUiAutomationElement<E>> extends
-    BaseDroidDriver {
-  // TODO: magic const from UiAutomator, but may not be useful
-  /**
-   * This value has the greatest bearing on the appearance of test execution
-   * speeds. This value is used as the minimum time to wait before considering
-   * the UI idle after each action.
-   */
-  private static final long QUIET_TIME_TO_BE_CONSIDERD_IDLE_STATE = 500;// ms
-
-  private final BaseUiAutomationContext<E> context;
-  private final UiAutomationUiDevice uiDevice;
-
-  protected BaseUiAutomationDriver(Instrumentation instrumentation) {
-    this.context = newContext(instrumentation);
-    this.uiDevice = new UiAutomationUiDevice(context);
-  }
-
-  protected abstract BaseUiAutomationContext<E> newContext(Instrumentation instrumentation);
-
-  @Override
-  protected E getNewRootElement() {
-    return context.getUiElement(getRootNode(), null /* parent */);
-  }
-
-  @Override
-  protected BaseUiAutomationContext<E> getContext() {
-    return context;
-  }
-
-  private AccessibilityNodeInfo getRootNode() {
-    final long timeoutMillis = getPoller().getTimeoutMillis();
-    context.callUiAutomation(new UiAutomationCallable<Void>() {
-      @Override
-      public Void call(UiAutomation uiAutomation) {
-        try {
-          uiAutomation.waitForIdle(QUIET_TIME_TO_BE_CONSIDERD_IDLE_STATE, timeoutMillis);
-          return null;
-        } catch (java.util.concurrent.TimeoutException e) {
-          throw new TimeoutException(e);
-        }
-      }
-    });
-
-    long end = SystemClock.uptimeMillis() + timeoutMillis;
-    while (true) {
-      AccessibilityNodeInfo root =
-          context.callUiAutomation(new UiAutomationCallable<AccessibilityNodeInfo>() {
-            @Override
-            public AccessibilityNodeInfo call(UiAutomation uiAutomation) {
-              return uiAutomation.getRootInActiveWindow();
-            }
-          });
-      if (root != null) {
-        return root;
-      }
-      long remainingMillis = end - SystemClock.uptimeMillis();
-      if (remainingMillis < 0) {
-        throw new TimeoutException(
-            String.format("Timed out after %d milliseconds waiting for root AccessibilityNodeInfo",
-                timeoutMillis));
-      }
-      SystemClock.sleep(Math.min(250, remainingMillis));
-    }
-  }
-
-  /**
-   * Some widgets fail to trigger some AccessibilityEvent's after actions,
-   * resulting in stale AccessibilityNodeInfo's. As a work-around, force to
-   * clear the AccessibilityNodeInfoCache.
-   */
-  public void clearAccessibilityNodeInfoCache() {
-    Logs.call(this, "clearAccessibilityNodeInfoCache");
-    uiDevice.sleep();
-    uiDevice.wakeUp();
-  }
-
-  /**
-   * {@link #clearAccessibilityNodeInfoCache} causes the screen to blink. This
-   * method clears the cache without blinking by employing an implementation
-   * detail of AccessibilityNodeInfoCache. This is a hack; use it at your own
-   * discretion.
-   */
-  public void clearAccessibilityNodeInfoCacheHack() {
-    Logs.call(this, "clearAccessibilityNodeInfoCacheHack");
-    AccessibilityManager accessibilityManager =
-        (AccessibilityManager) context.getInstrumentation().getTargetContext()
-            .getSystemService(Context.ACCESSIBILITY_SERVICE);
-    accessibilityManager.sendAccessibilityEvent(AccessibilityEvent
-        .obtain(AccessibilityEvent.TYPE_WINDOW_STATE_CHANGED));
-  }
-
-  @Override
-  public UiAutomationUiDevice getUiDevice() {
-    return uiDevice;
-  }
-}
diff --git a/src/com/google/android/droiddriver/uiautomation/base/BaseUiAutomationElement.java b/src/com/google/android/droiddriver/uiautomation/base/BaseUiAutomationElement.java
deleted file mode 100644
index a27a3eb..0000000
--- a/src/com/google/android/droiddriver/uiautomation/base/BaseUiAutomationElement.java
+++ /dev/null
@@ -1,220 +0,0 @@
-/*
- * Copyright (C) 2013 DroidDriver committers
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package com.google.android.droiddriver.uiautomation.base;
-
-import static com.google.android.droiddriver.util.Strings.charSequenceToString;
-
-import android.app.UiAutomation;
-import android.app.UiAutomation.AccessibilityEventFilter;
-import android.graphics.Rect;
-import android.view.accessibility.AccessibilityEvent;
-import android.view.accessibility.AccessibilityNodeInfo;
-
-import com.google.android.droiddriver.actions.InputInjector;
-import com.google.android.droiddriver.base.BaseUiElement;
-import com.google.android.droiddriver.base.UiElementActor;
-import com.google.android.droiddriver.finders.Attribute;
-import com.google.android.droiddriver.util.Preconditions;
-
-import java.util.ArrayList;
-import java.util.Collections;
-import java.util.EnumMap;
-import java.util.List;
-import java.util.Map;
-import java.util.concurrent.FutureTask;
-import java.util.concurrent.TimeoutException;
-
-/**
- * A UiElement that gets attributes via the Accessibility API.
- */
-public class BaseUiAutomationElement<E extends BaseUiAutomationElement<E>> extends BaseUiElement {
-  private static final AccessibilityEventFilter ANY_EVENT_FILTER = new AccessibilityEventFilter() {
-    @Override
-    public boolean accept(AccessibilityEvent arg0) {
-      return true;
-    }
-  };
-
-  private final AccessibilityNodeInfo node;
-  private final BaseUiAutomationContext<E> context;
-  private final Map<Attribute, Object> attributes;
-  private final boolean visible;
-  private final Rect visibleBounds;
-  private final E parent;
-  private final List<E> children;
-
-  /**
-   * A snapshot of all attributes is taken at construction. The attributes of a
-   * {@code UiAutomationElement} instance are immutable. If the underlying
-   * {@link AccessibilityNodeInfo} is updated, a new {@code UiAutomationElement}
-   * instance will be created in
-   * {@link com.google.android.droiddriver.DroidDriver#refreshUiElementTree}.
-   */
-  protected BaseUiAutomationElement(BaseUiAutomationContext<E> context, AccessibilityNodeInfo node,
-      E parent, UiElementActor UiElementActor) {
-    super(UiElementActor);
-    this.node = Preconditions.checkNotNull(node);
-    this.context = Preconditions.checkNotNull(context);
-    this.parent = parent;
-
-    Map<Attribute, Object> attribs = new EnumMap<Attribute, Object>(Attribute.class);
-    put(attribs, Attribute.PACKAGE, charSequenceToString(node.getPackageName()));
-    put(attribs, Attribute.CLASS, charSequenceToString(node.getClassName()));
-    put(attribs, Attribute.TEXT, charSequenceToString(node.getText()));
-    put(attribs, Attribute.CONTENT_DESC, charSequenceToString(node.getContentDescription()));
-    put(attribs, Attribute.RESOURCE_ID, charSequenceToString(node.getViewIdResourceName()));
-    put(attribs, Attribute.CHECKABLE, node.isCheckable());
-    put(attribs, Attribute.CHECKED, node.isChecked());
-    put(attribs, Attribute.CLICKABLE, node.isClickable());
-    put(attribs, Attribute.ENABLED, node.isEnabled());
-    put(attribs, Attribute.FOCUSABLE, node.isFocusable());
-    put(attribs, Attribute.FOCUSED, node.isFocused());
-    put(attribs, Attribute.LONG_CLICKABLE, node.isLongClickable());
-    put(attribs, Attribute.PASSWORD, node.isPassword());
-    put(attribs, Attribute.SCROLLABLE, node.isScrollable());
-    if (node.getTextSelectionStart() >= 0
-        && node.getTextSelectionStart() != node.getTextSelectionEnd()) {
-      attribs.put(Attribute.SELECTION_START, node.getTextSelectionStart());
-      attribs.put(Attribute.SELECTION_END, node.getTextSelectionEnd());
-    }
-    put(attribs, Attribute.SELECTED, node.isSelected());
-    put(attribs, Attribute.BOUNDS, getBounds(node));
-    attributes = Collections.unmodifiableMap(attribs);
-
-    // Order matters as getVisibleBounds depends on visible
-    visible = node.isVisibleToUser();
-    visibleBounds = getVisibleBounds(node);
-    List<E> mutableChildren = buildChildren(node);
-    this.children = mutableChildren == null ? null : Collections.unmodifiableList(mutableChildren);
-  }
-
-  private void put(Map<Attribute, Object> attribs, Attribute key, Object value) {
-    if (value != null) {
-      attribs.put(key, value);
-    }
-  }
-
-  @SuppressWarnings("unchecked")
-  private List<E> buildChildren(AccessibilityNodeInfo node) {
-    List<E> children;
-    int childCount = node.getChildCount();
-    if (childCount == 0) {
-      children = null;
-    } else {
-      children = new ArrayList<E>(childCount);
-      for (int i = 0; i < childCount; i++) {
-        AccessibilityNodeInfo child = node.getChild(i);
-        if (child != null) {
-          children.add(context.getUiElement(child, (E) this));
-        }
-      }
-    }
-    return children;
-  }
-
-  private Rect getBounds(AccessibilityNodeInfo node) {
-    Rect rect = new Rect();
-    node.getBoundsInScreen(rect);
-    return rect;
-  }
-
-  private Rect getVisibleBounds(AccessibilityNodeInfo node) {
-    if (!visible) {
-      return new Rect();
-    }
-    Rect visibleBounds = getBounds();
-    E parent = getParent();
-    Rect parentBounds;
-    while (parent != null) {
-      parentBounds = parent.getBounds();
-      visibleBounds.intersect(parentBounds);
-      parent = parent.getParent();
-    }
-    return visibleBounds;
-  }
-
-  @Override
-  public Rect getVisibleBounds() {
-    return visibleBounds;
-  }
-
-  @Override
-  public boolean isVisible() {
-    return visible;
-  }
-
-  @Override
-  public E getParent() {
-    return parent;
-  }
-
-  @Override
-  protected List<E> getChildren() {
-    return children;
-  }
-
-  @Override
-  protected Map<Attribute, Object> getAttributes() {
-    return attributes;
-  }
-
-  @Override
-  public InputInjector getInjector() {
-    return context.getInjector();
-  }
-
-  /**
-   * Note: This implementation of {@code doPerformAndWait} clears the
-   * {@code AccessibilityEvent} queue.
-   */
-  @Override
-  protected void doPerformAndWait(final FutureTask<Boolean> futureTask, final long timeoutMillis) {
-    context.callUiAutomation(new UiAutomationCallable<Void>() {
-
-      @Override
-      public Void call(UiAutomation uiAutomation) {
-        try {
-          uiAutomation.executeAndWaitForEvent(futureTask, ANY_EVENT_FILTER, timeoutMillis);
-        } catch (TimeoutException e) {
-          // This is for sync'ing with Accessibility API on best-effort because
-          // it is not reliable.
-          // Exception is ignored here. Tests will fail anyways if this is
-          // critical.
-          // Actions should usually trigger some AccessibilityEvent's, but some
-          // widgets fail to do so, resulting in stale AccessibilityNodeInfo's.
-          // As a work-around, force to clear the AccessibilityNodeInfoCache.
-          // A legitimate case of no AccessibilityEvent is when scrolling has
-          // reached the end, but we cannot tell whether it's legitimate or the
-          // widget has bugs, so clearAccessibilityNodeInfoCache anyways.
-          context.getDriver().clearAccessibilityNodeInfoCacheHack();
-        }
-        return null;
-      }
-
-    });
-  }
-
-  /**
-   * Gets the AccessibilityNodeInfo used to create this UiElement. The
-   * attributes of this UiElement are based on a snapshot of the
-   * AccessibilityNodeInfo at construction time. If the Accessibility framework
-   * updated it later, the attributes may not match.
-   */
-  public AccessibilityNodeInfo getNode() {
-    return node;
-  }
-}
diff --git a/src/com/google/android/droiddriver/validators/DefaultAccessibilityValidator.java b/src/com/google/android/droiddriver/validators/DefaultAccessibilityValidator.java
new file mode 100644
index 0000000..ff1d095
--- /dev/null
+++ b/src/com/google/android/droiddriver/validators/DefaultAccessibilityValidator.java
@@ -0,0 +1,34 @@
+/*
+ * Copyright (C) 2013 DroidDriver committers
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.android.droiddriver.validators;
+
+import android.text.TextUtils;
+
+import com.google.android.droiddriver.UiElement;
+
+/**
+ * Validates accessibility.
+ */
+// TODO: Treats various types of UiElement as TalkBack does.
+public class DefaultAccessibilityValidator implements Validator {
+  @Override
+  public boolean isValid(UiElement element) {
+    return element.getParent() != null // don't check root
+        && TextUtils.isEmpty(element.getContentDescription())
+        && TextUtils.isEmpty(element.getText());
+  }
+}
diff --git a/src/com/google/android/droiddriver/exceptions/ElementNotVisibleException.java b/src/com/google/android/droiddriver/validators/Validator.java
index b3ac86e..f7812ed 100644
--- a/src/com/google/android/droiddriver/exceptions/ElementNotVisibleException.java
+++ b/src/com/google/android/droiddriver/validators/Validator.java
@@ -14,17 +14,18 @@
  * limitations under the License.
  */
 
-package com.google.android.droiddriver.exceptions;
+package com.google.android.droiddriver.validators;
 
 import com.google.android.droiddriver.UiElement;
 
 /**
- * Thrown when an element is not visible on screen, therefore cannot be
- * interacted with.
+ * Interface for validating a UiElement, checked when an action is performed.
+ * For example, in general accessibility mandates that an actionable UiElement
+ * has content description or text.
  */
-@SuppressWarnings("serial")
-public class ElementNotVisibleException extends DroidDriverException {
-  public ElementNotVisibleException(UiElement element) {
-    super("Invisible on screen: " + element);
-  }
+public interface Validator {
+  /**
+   * Returns true if {@code element} is valid.
+   */
+  boolean isValid(UiElement element);
 }
diff --git a/src/com/google/android/droiddriver/uiautomation/base/UiAutomationCallable.java b/src/com/google/android/droiddriver/validators/VisibilityValidator.java
index 36a5292..44570cf 100644
--- a/src/com/google/android/droiddriver/uiautomation/base/UiAutomationCallable.java
+++ b/src/com/google/android/droiddriver/validators/VisibilityValidator.java
@@ -14,10 +14,16 @@
  * limitations under the License.
  */
 
-package com.google.android.droiddriver.uiautomation.base;
+package com.google.android.droiddriver.validators;
 
-import android.app.UiAutomation;
+import com.google.android.droiddriver.UiElement;
 
-public interface UiAutomationCallable<T> {
-  T call(UiAutomation uiAutomation);
-}
\ No newline at end of file
+/**
+ * Validates visibility.
+ */
+public class VisibilityValidator implements Validator {
+  @Override
+  public boolean isValid(UiElement element) {
+    return element.isVisible();
+  }
+}