introduce AccessibilityEventScrollStepStrategy which is

a simple ScrollStepStrategy for UiAutomation and behaves like UiScrollable.
rename SentinelScroller to StepBasedScroller

Change-Id: I424140817d53c63165a66a5fffb5cae24c47288b

14 files changed, 474 insertions, 282 deletions

diff --git a/src/com/google/android/droiddriver/UiElement.java b/src/com/google/android/droiddriver/UiElement.java
index 1ae6254..924197f 100644
--- a/src/com/google/android/droiddriver/UiElement.java
+++ b/src/com/google/android/droiddriver/UiElement.java
@@ -19,6 +19,7 @@ package com.google.android.droiddriver;
 import android.graphics.Rect;
 
 import com.google.android.droiddriver.actions.Action;
+import com.google.android.droiddriver.actions.InputInjector;
 import com.google.android.droiddriver.exceptions.ElementNotVisibleException;
 import com.google.android.droiddriver.finders.Attribute;
 import com.google.android.droiddriver.instrumentation.InstrumentationDriver;
@@ -225,4 +226,9 @@ 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/base/BaseUiElement.java b/src/com/google/android/droiddriver/base/BaseUiElement.java
index 6a2f88c..9cddc71 100644
--- a/src/com/google/android/droiddriver/base/BaseUiElement.java
+++ b/src/com/google/android/droiddriver/base/BaseUiElement.java
@@ -211,8 +211,6 @@ public abstract class BaseUiElement implements UiElement {
 
   protected abstract List<? extends BaseUiElement> getChildren();
 
-  protected abstract InputInjector getInjector();
-
   private void checkVisible() {
     if (!isVisible()) {
       throw new ElementNotVisibleException(this);
diff --git a/src/com/google/android/droiddriver/helpers/ScrollerHelper.java b/src/com/google/android/droiddriver/helpers/ScrollerHelper.java
new file mode 100644
index 0000000..dc946e7
--- /dev/null
+++ b/src/com/google/android/droiddriver/helpers/ScrollerHelper.java
@@ -0,0 +1,51 @@
+/*
+ * 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.helpers;
+
+import com.google.android.droiddriver.DroidDriver;
+import com.google.android.droiddriver.UiElement;
+import com.google.android.droiddriver.exceptions.ElementNotFoundException;
+import com.google.android.droiddriver.finders.Finder;
+import com.google.android.droiddriver.scroll.Scroller;
+
+/**
+ * Helper for Scroller.
+ */
+public class ScrollerHelper {
+  private final DroidDriver driver;
+  private final Finder containerFinder;
+  private final Scroller scroller;
+
+  public ScrollerHelper(Scroller scroller, DroidDriver driver, Finder containerFinder) {
+    this.scroller = scroller;
+    this.driver = driver;
+    this.containerFinder = containerFinder;
+  }
+
+  public UiElement scrollTo(Finder itemFinder) {
+    return scroller.scrollTo(driver, containerFinder, itemFinder);
+  }
+
+  public boolean canScrollTo(Finder itemFinder) {
+    try {
+      scrollTo(itemFinder);
+      return true;
+    } catch (ElementNotFoundException e) {
+      return false;
+    }
+  }
+}
diff --git a/src/com/google/android/droiddriver/instrumentation/ViewElement.java b/src/com/google/android/droiddriver/instrumentation/ViewElement.java
index 186681f..070d14f 100644
--- a/src/com/google/android/droiddriver/instrumentation/ViewElement.java
+++ b/src/com/google/android/droiddriver/instrumentation/ViewElement.java
@@ -255,7 +255,7 @@ public class ViewElement extends BaseUiElement {
   }
 
   @Override
-  protected InputInjector getInjector() {
+  public InputInjector getInjector() {
     return context.getInjector();
   }
 }
diff --git a/src/com/google/android/droiddriver/scroll/AbstractSentinelStrategy.java b/src/com/google/android/droiddriver/scroll/AbstractSentinelStrategy.java
deleted file mode 100644
index 2c339ad..0000000
--- a/src/com/google/android/droiddriver/scroll/AbstractSentinelStrategy.java
+++ /dev/null
@@ -1,202 +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.scroll;
-
-import android.util.Log;
-
-import com.google.android.droiddriver.DroidDriver;
-import com.google.android.droiddriver.UiElement;
-import com.google.android.droiddriver.exceptions.ElementNotFoundException;
-import com.google.android.droiddriver.finders.By;
-import com.google.android.droiddriver.finders.Finder;
-import com.google.android.droiddriver.scroll.Direction.DirectionConverter;
-import com.google.android.droiddriver.scroll.Direction.LogicalDirection;
-import com.google.android.droiddriver.scroll.Direction.PhysicalDirection;
-import com.google.android.droiddriver.util.Logs;
-import com.google.common.base.Predicate;
-import com.google.common.base.Predicates;
-
-import java.util.List;
-
-/**
- * Base {@link SentinelStrategy} for common code.
- */
-public abstract class AbstractSentinelStrategy implements SentinelStrategy {
-
-  /**
-   * Gets sentinel based on {@link Predicate}.
-   */
-  public static abstract class GetStrategy {
-    protected final Predicate<? super UiElement> predicate;
-    protected final String description;
-
-    protected GetStrategy(Predicate<? super UiElement> predicate, String description) {
-      this.predicate = predicate;
-      this.description = description;
-    }
-
-    /**
-     * Gets the sentinel, which must be an immediate child of {@code container}
-     * -- not a descendant. Note this could be null if {@code container} has not
-     * finished updating.
-     */
-    public UiElement getSentinel(UiElement container) {
-      return getSentinel(container.getChildren(predicate));
-    }
-
-    protected abstract UiElement getSentinel(List<? extends UiElement> children);
-
-    @Override
-    public String toString() {
-      return description;
-    }
-  }
-
-  /**
-   * Decorates an existing {@link GetStrategy} by adding another
-   * {@link Predicate}.
-   */
-  public static class MorePredicateGetStrategy extends GetStrategy {
-    private final GetStrategy original;
-
-    public MorePredicateGetStrategy(GetStrategy original,
-        Predicate<? super UiElement> extraPredicate, String extraDescription) {
-      super(Predicates.and(original.predicate, extraPredicate), extraDescription
-          + original.description);
-      this.original = original;
-    }
-
-    @Override
-    protected UiElement getSentinel(List<? extends UiElement> children) {
-      return original.getSentinel(children);
-    }
-  }
-
-  /**
-   * Returns the first child as the sentinel.
-   */
-  public static final GetStrategy FIRST_CHILD_GETTER = new GetStrategy(Predicates.alwaysTrue(),
-      "FIRST_CHILD") {
-    @Override
-    protected UiElement getSentinel(List<? extends UiElement> children) {
-      return children.isEmpty() ? null : children.get(0);
-    }
-  };
-
-  /**
-   * Returns the last child as the sentinel.
-   */
-  public static final GetStrategy LAST_CHILD_GETTER = new GetStrategy(Predicates.alwaysTrue(),
-      "LAST_CHILD") {
-    @Override
-    protected UiElement getSentinel(List<? extends UiElement> children) {
-      return children.isEmpty() ? null : children.get(children.size() - 1);
-    }
-  };
-
-  /**
-   * Returns the second last child as the sentinel. Useful when the activity
-   * always shows the last child as an anchor (for example a footer).
-   * <p>
-   * Sometimes uiautomatorviewer may not show the anchor as the last child, due
-   * to the reordering by layout described in {@link UiElement#getChildren}.
-   * This is not a problem with UiAutomationDriver because it sees the same as
-   * uiautomatorviewer does, but could be a problem with InstrumentationDriver.
-   * </p>
-   */
-  public static final GetStrategy SECOND_LAST_CHILD_GETTER = new GetStrategy(
-      Predicates.alwaysTrue(), "SECOND_LAST_CHILD") {
-    @Override
-    protected UiElement getSentinel(List<? extends UiElement> children) {
-      return children.size() < 2 ? null : children.get(children.size() - 2);
-    }
-  };
-
-  /**
-   * Returns the second child as the sentinel. Useful when the activity shows a
-   * fixed first child.
-   */
-  public static final GetStrategy SECOND_CHILD_GETTER = new GetStrategy(Predicates.alwaysTrue(),
-      "SECOND_CHILD") {
-    @Override
-    protected UiElement getSentinel(List<? extends UiElement> children) {
-      return children.size() <= 1 ? null : children.get(1);
-    }
-  };
-
-  // Make sure sentinel exists in container
-  private static class SentinelFinder implements Finder {
-    private final GetStrategy getStrategy;
-
-    public SentinelFinder(GetStrategy getStrategy) {
-      this.getStrategy = getStrategy;
-    }
-
-    @Override
-    public UiElement find(UiElement container) {
-      UiElement sentinel = getStrategy.getSentinel(container);
-      if (sentinel == null) {
-        throw new ElementNotFoundException(this);
-      }
-      Logs.log(Log.INFO, "Found match: " + sentinel);
-      return sentinel;
-    }
-
-    @Override
-    public String toString() {
-      return String.format("SentinelFinder{%s}", getStrategy);
-    }
-  }
-
-  private final GetStrategy backwardGetStrategy;
-  private final GetStrategy forwardGetStrategy;
-  private final DirectionConverter directionConverter;
-  private final SentinelFinder backwardSentinelFinder;
-  private final SentinelFinder forwardSentinelFinder;
-
-  public AbstractSentinelStrategy(GetStrategy backwardGetStrategy, GetStrategy forwardGetStrategy,
-      DirectionConverter directionConverter) {
-    this.backwardGetStrategy = backwardGetStrategy;
-    this.forwardGetStrategy = forwardGetStrategy;
-    this.directionConverter = directionConverter;
-    this.backwardSentinelFinder = new SentinelFinder(backwardGetStrategy);
-    this.forwardSentinelFinder = new SentinelFinder(forwardGetStrategy);
-  }
-
-  protected UiElement getSentinel(DroidDriver driver, Finder containerFinder,
-      PhysicalDirection direction) {
-    Logs.call(this, "getSentinel", driver, containerFinder, direction);
-    Finder sentinelFinder;
-    LogicalDirection logicalDirection = directionConverter.toLogicalDirection(direction);
-    if (logicalDirection == LogicalDirection.BACKWARD) {
-      sentinelFinder = By.chain(containerFinder, backwardSentinelFinder);
-    } else {
-      sentinelFinder = By.chain(containerFinder, forwardSentinelFinder);
-    }
-    return driver.on(sentinelFinder);
-  }
-
-  @Override
-  public final DirectionConverter getDirectionConverter() {
-    return directionConverter;
-  }
-
-  @Override
-  public String toString() {
-    return String.format("{backwardGetStrategy=%s, forwardGetStrategy=%s}", backwardGetStrategy,
-        forwardGetStrategy);
-  }
-}
diff --git a/src/com/google/android/droiddriver/scroll/AccessibilityEventScrollStepStrategy.java b/src/com/google/android/droiddriver/scroll/AccessibilityEventScrollStepStrategy.java
new file mode 100644
index 0000000..0333d77
--- /dev/null
+++ b/src/com/google/android/droiddriver/scroll/AccessibilityEventScrollStepStrategy.java
@@ -0,0 +1,91 @@
+/*
+ * 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.scroll;
+
+import android.app.UiAutomation;
+import android.app.UiAutomation.AccessibilityEventFilter;
+import android.view.accessibility.AccessibilityEvent;
+
+import com.google.android.droiddriver.DroidDriver;
+import com.google.android.droiddriver.UiElement;
+import com.google.android.droiddriver.actions.SwipeAction;
+import com.google.android.droiddriver.finders.Finder;
+import com.google.android.droiddriver.scroll.Direction.DirectionConverter;
+import com.google.android.droiddriver.scroll.Direction.PhysicalDirection;
+
+import java.util.concurrent.TimeoutException;
+
+/**
+ * A {@link ScrollStepStrategy} that determines whether more scrolling is
+ * possible by checking the {@link AccessibilityEvent} returned by
+ * {@link android.app.UiAutomation}.
+ * <p>
+ * This implementation behaves just like the <a href=
+ * "http://developer.android.com/tools/help/uiautomator/UiScrollable.html"
+ * >UiScrollable</a> class. It may not work in all cases. For instance,
+ * sometimes {@link android.support.v4.widget.DrawerLayout} does not send
+ * correct {@link AccessibilityEvent}s after scrolling.
+ * </p>
+ */
+public class AccessibilityEventScrollStepStrategy implements ScrollStepStrategy {
+  private static final AccessibilityEventFilter SCROLL_EVENT_FILTER =
+      new AccessibilityEventFilter() {
+        @Override
+        public boolean accept(AccessibilityEvent arg0) {
+          return (arg0.getEventType() & AccessibilityEvent.TYPE_VIEW_SCROLLED) != 0;
+        }
+      };
+
+  private final UiAutomation uiAutomation;
+  private final long scrollEventTimeoutMillis;
+  private final DirectionConverter directionConverter;
+
+  public AccessibilityEventScrollStepStrategy(UiAutomation uiAutomation,
+      long scrollEventTimeoutMillis, DirectionConverter converter) {
+    this.uiAutomation = uiAutomation;
+    this.scrollEventTimeoutMillis = scrollEventTimeoutMillis;
+    this.directionConverter = converter;
+  }
+
+  @Override
+  public boolean scroll(DroidDriver driver, Finder containerFinder,
+      final PhysicalDirection direction) {
+    final UiElement container = driver.on(containerFinder);
+    try {
+      uiAutomation.executeAndWaitForEvent(new Runnable() {
+        @Override
+        public void run() {
+          SwipeAction.toScroll(direction).perform(container.getInjector(), container);
+        }
+      }, SCROLL_EVENT_FILTER, scrollEventTimeoutMillis);
+    } catch (TimeoutException e) {
+      // If no TYPE_VIEW_SCROLLED event, no more scrolling is possible
+      return false;
+    }
+    return true;
+  }
+
+  @Override
+  public final DirectionConverter getDirectionConverter() {
+    return directionConverter;
+  }
+
+  @Override
+  public String toString() {
+    return String.format("AccessibilityEventScrollStepStrategy{scrollEventTimeoutMillis=%d}",
+        scrollEventTimeoutMillis);
+  }
+}
diff --git a/src/com/google/android/droiddriver/scroll/BaseSentinelStrategy.java b/src/com/google/android/droiddriver/scroll/BaseSentinelStrategy.java
new file mode 100644
index 0000000..709a068
--- /dev/null
+++ b/src/com/google/android/droiddriver/scroll/BaseSentinelStrategy.java
@@ -0,0 +1,96 @@
+/*
+ * 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.scroll;
+
+import android.util.Log;
+
+import com.google.android.droiddriver.DroidDriver;
+import com.google.android.droiddriver.UiElement;
+import com.google.android.droiddriver.exceptions.ElementNotFoundException;
+import com.google.android.droiddriver.finders.By;
+import com.google.android.droiddriver.finders.Finder;
+import com.google.android.droiddriver.scroll.Direction.DirectionConverter;
+import com.google.android.droiddriver.scroll.Direction.LogicalDirection;
+import com.google.android.droiddriver.scroll.Direction.PhysicalDirection;
+import com.google.android.droiddriver.util.Logs;
+
+/**
+ * Base class for {@link SentinelStrategy}.
+ */
+public abstract class BaseSentinelStrategy implements SentinelStrategy {
+
+  // Make sure sentinel exists in container
+  private static class SentinelFinder implements Finder {
+    private final Getter getter;
+
+    public SentinelFinder(Getter getter) {
+      this.getter = getter;
+    }
+
+    @Override
+    public UiElement find(UiElement container) {
+      UiElement sentinel = getter.getSentinel(container);
+      if (sentinel == null) {
+        throw new ElementNotFoundException(this);
+      }
+      Logs.log(Log.INFO, "Found match: " + sentinel);
+      return sentinel;
+    }
+
+    @Override
+    public String toString() {
+      return String.format("SentinelFinder{%s}", getter);
+    }
+  }
+
+  private final Getter backwardGetter;
+  private final Getter forwardGetter;
+  private final DirectionConverter directionConverter;
+  private final SentinelFinder backwardSentinelFinder;
+  private final SentinelFinder forwardSentinelFinder;
+
+  protected BaseSentinelStrategy(Getter backwardGetter, Getter forwardGetter,
+      DirectionConverter directionConverter) {
+    this.backwardGetter = backwardGetter;
+    this.forwardGetter = forwardGetter;
+    this.directionConverter = directionConverter;
+    this.backwardSentinelFinder = new SentinelFinder(backwardGetter);
+    this.forwardSentinelFinder = new SentinelFinder(forwardGetter);
+  }
+
+  protected UiElement getSentinel(DroidDriver driver, Finder containerFinder,
+      PhysicalDirection direction) {
+    Logs.call(this, "getSentinel", driver, containerFinder, direction);
+    Finder sentinelFinder;
+    LogicalDirection logicalDirection = directionConverter.toLogicalDirection(direction);
+    if (logicalDirection == LogicalDirection.BACKWARD) {
+      sentinelFinder = By.chain(containerFinder, backwardSentinelFinder);
+    } else {
+      sentinelFinder = By.chain(containerFinder, forwardSentinelFinder);
+    }
+    return driver.on(sentinelFinder);
+  }
+
+  @Override
+  public final DirectionConverter getDirectionConverter() {
+    return directionConverter;
+  }
+
+  @Override
+  public String toString() {
+    return String.format("{backwardGetter=%s, forwardGetter=%s}", backwardGetter, forwardGetter);
+  }
+}
diff --git a/src/com/google/android/droiddriver/scroll/DynamicSentinelStrategy.java b/src/com/google/android/droiddriver/scroll/DynamicSentinelStrategy.java
index 3ae0e50..bf8c6d3 100644
--- a/src/com/google/android/droiddriver/scroll/DynamicSentinelStrategy.java
+++ b/src/com/google/android/droiddriver/scroll/DynamicSentinelStrategy.java
@@ -34,7 +34,7 @@ import com.google.common.base.Objects;
  * used, which skips invisible children, or in the case of dynamic list, which
  * shows more items when scrolling beyond the end.
  */
-public class DynamicSentinelStrategy extends AbstractSentinelStrategy {
+public class DynamicSentinelStrategy extends BaseSentinelStrategy {
 
   /**
    * Interface for determining whether sentinel is updated.
@@ -100,7 +100,7 @@ public class DynamicSentinelStrategy extends AbstractSentinelStrategy {
       String newString = getUniqueStringFromSentinel(newSentinel);
       // A legitimate case for newString being null is when newSentinel is
       // partially shown. We return true to allow further scrolling. But program
-      // error could also cause this, e.g. a bad choice of GetStrategy, which
+      // error could also cause this, e.g. a bad choice of Getter, which
       // results in unnecessary scroll actions that have no visual effect. This
       // log helps troubleshooting in the latter case.
       if (newString == null) {
@@ -176,36 +176,32 @@ public class DynamicSentinelStrategy extends AbstractSentinelStrategy {
   private final IsUpdatedStrategy isUpdatedStrategy;
 
   /**
-   * Constructs with {@code GetStrategy}s that decorate the given
-   * {@code GetStrategy}s with {@link UiElement#VISIBLE}, and the given
-   * {@code isUpdatedStrategy} and {@code directionConverter}. Be careful with
-   * {@code GetStrategy}s: the sentinel after each scroll should be unique.
+   * Constructs with {@code Getter}s that decorate the given {@code Getter}s
+   * with {@link UiElement#VISIBLE}, and the given {@code isUpdatedStrategy} and
+   * {@code directionConverter}. Be careful with {@code Getter}s: the sentinel
+   * after each scroll should be unique.
    */
-  public DynamicSentinelStrategy(IsUpdatedStrategy isUpdatedStrategy,
-      GetStrategy backwardGetStrategy, GetStrategy forwardGetStrategy,
-      DirectionConverter directionConverter) {
-    super(new MorePredicateGetStrategy(backwardGetStrategy, UiElement.VISIBLE, "VISIBLE_"),
-        new MorePredicateGetStrategy(forwardGetStrategy, UiElement.VISIBLE, "VISIBLE_"),
-        directionConverter);
+  public DynamicSentinelStrategy(IsUpdatedStrategy isUpdatedStrategy, Getter backwardGetter,
+      Getter forwardGetter, DirectionConverter directionConverter) {
+    super(new MorePredicateGetter(backwardGetter, UiElement.VISIBLE, "VISIBLE_"),
+        new MorePredicateGetter(forwardGetter, UiElement.VISIBLE, "VISIBLE_"), directionConverter);
     this.isUpdatedStrategy = isUpdatedStrategy;
   }
 
   /**
    * Defaults to the standard {@link DirectionConverter}.
    */
-  public DynamicSentinelStrategy(IsUpdatedStrategy isUpdatedStrategy,
-      GetStrategy backwardGetStrategy, GetStrategy forwardGetStrategy) {
-    this(isUpdatedStrategy, backwardGetStrategy, forwardGetStrategy,
-        DirectionConverter.STANDARD_CONVERTER);
+  public DynamicSentinelStrategy(IsUpdatedStrategy isUpdatedStrategy, Getter backwardGetter,
+      Getter forwardGetter) {
+    this(isUpdatedStrategy, backwardGetter, forwardGetter, DirectionConverter.STANDARD_CONVERTER);
   }
 
   /**
    * Defaults to LAST_CHILD_GETTER for forward scrolling, and the standard
    * {@link DirectionConverter}.
    */
-  public DynamicSentinelStrategy(IsUpdatedStrategy isUpdatedStrategy,
-      GetStrategy backwardGetStrategy) {
-    this(isUpdatedStrategy, backwardGetStrategy, LAST_CHILD_GETTER,
+  public DynamicSentinelStrategy(IsUpdatedStrategy isUpdatedStrategy, Getter backwardGetter) {
+    this(isUpdatedStrategy, backwardGetter, LAST_CHILD_GETTER,
         DirectionConverter.STANDARD_CONVERTER);
   }
 
diff --git a/src/com/google/android/droiddriver/scroll/ScrollStepStrategy.java b/src/com/google/android/droiddriver/scroll/ScrollStepStrategy.java
new file mode 100644
index 0000000..5bdeb83
--- /dev/null
+++ b/src/com/google/android/droiddriver/scroll/ScrollStepStrategy.java
@@ -0,0 +1,52 @@
+/*
+ * 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.scroll;
+
+import com.google.android.droiddriver.DroidDriver;
+import com.google.android.droiddriver.finders.Finder;
+import com.google.android.droiddriver.scroll.Direction.DirectionConverter;
+import com.google.android.droiddriver.scroll.Direction.PhysicalDirection;
+
+/**
+ * Interface for determining whether scrolling is possible.
+ */
+public interface ScrollStepStrategy {
+  /**
+   * Tries to scroll {@code containerFinder} in {@code direction}. Returns
+   * whether scrolling is effective.
+   *
+   * @param driver
+   * @param containerFinder Finder for the container that can scroll, for
+   *        instance a ListView
+   * @param direction
+   * @return whether scrolling is effective
+   */
+  boolean scroll(DroidDriver driver, Finder containerFinder, PhysicalDirection direction);
+
+  /**
+   * Returns the {@link DirectionConverter}.
+   */
+  DirectionConverter getDirectionConverter();
+
+  /**
+   * {@inheritDoc}
+   *
+   * <p>
+   * It is recommended that this method return a description to help debugging.
+   */
+  @Override
+  String toString();
+}
diff --git a/src/com/google/android/droiddriver/scroll/Scrollers.java b/src/com/google/android/droiddriver/scroll/Scrollers.java
new file mode 100644
index 0000000..ddf9610
--- /dev/null
+++ b/src/com/google/android/droiddriver/scroll/Scrollers.java
@@ -0,0 +1,48 @@
+/*
+ * 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.scroll;
+
+import android.app.UiAutomation;
+
+import com.google.android.droiddriver.scroll.Direction.DirectionConverter;
+
+/**
+ * Static utility methods pertaining to {@link Scroller} instances.
+ */
+public class Scrollers {
+  /**
+   * Returns a new default Scroller that works in simple cases. In complex cases
+   * you may try a {@link StepBasedScroller} with a custom
+   * {@link ScrollStepStrategy}:
+   * <ul>
+   * <li>If the Scroller is used with InstrumentationDriver,
+   * StaticSentinelStrategy may work and it's the simplest.</li>
+   * <li>Otherwise, DynamicSentinelStrategy should work in all cases, including
+   * the case of dynamic list, which shows more items when scrolling beyond the
+   * end. On the other hand, it's complex and needs more configuration.</li>
+   * </ul>
+   */
+  public static Scroller newScroller(UiAutomation uiAutomation) {
+    if (uiAutomation != null) {
+      return new StepBasedScroller(new AccessibilityEventScrollStepStrategy(uiAutomation, 1000L,
+          DirectionConverter.STANDARD_CONVERTER));
+    }
+    // TODO: A {@link Scroller} that directly jumps to the view if an
+    // InstrumentationDriver is used.
+    return new StepBasedScroller(StaticSentinelStrategy.DEFAULT);
+  }
+}
diff --git a/src/com/google/android/droiddriver/scroll/SentinelStrategy.java b/src/com/google/android/droiddriver/scroll/SentinelStrategy.java
index 33c19e3..0330844 100644
--- a/src/com/google/android/droiddriver/scroll/SentinelStrategy.java
+++ b/src/com/google/android/droiddriver/scroll/SentinelStrategy.java
@@ -15,38 +15,110 @@
  */
 package com.google.android.droiddriver.scroll;
 
-import com.google.android.droiddriver.DroidDriver;
-import com.google.android.droiddriver.finders.Finder;
-import com.google.android.droiddriver.scroll.Direction.DirectionConverter;
-import com.google.android.droiddriver.scroll.Direction.PhysicalDirection;
+import com.google.android.droiddriver.UiElement;
+import com.google.common.base.Predicate;
+import com.google.common.base.Predicates;
+
+import java.util.List;
 
 /**
  * Interface for determining whether scrolling is possible based on a sentinel.
  */
-public interface SentinelStrategy {
+public interface SentinelStrategy extends ScrollStepStrategy {
+
   /**
-   * Tries to scroll {@code containerFinder} in {@code direction}. Returns
-   * whether scrolling is effective.
-   *
-   * @param driver
-   * @param containerFinder Finder for the container that can scroll, for
-   *        instance a ListView
-   * @param direction
-   * @return whether scrolling is effective
+   * Gets sentinel based on {@link Predicate}.
    */
-  boolean scroll(DroidDriver driver, Finder containerFinder, PhysicalDirection direction);
+  public static abstract class Getter {
+    protected final Predicate<? super UiElement> predicate;
+    protected final String description;
+
+    protected Getter(Predicate<? super UiElement> predicate, String description) {
+      this.predicate = predicate;
+      this.description = description;
+    }
+
+    /**
+     * Gets the sentinel, which must be an immediate child of {@code container}
+     * -- not a descendant. Note this could be null if {@code container} has not
+     * finished updating.
+     */
+    public UiElement getSentinel(UiElement container) {
+      return getSentinel(container.getChildren(predicate));
+    }
+
+    protected abstract UiElement getSentinel(List<? extends UiElement> children);
+
+    @Override
+    public String toString() {
+      return description;
+    }
+  }
 
   /**
-   * Returns the {@link DirectionConverter}.
+   * Decorates an existing {@link Getter} by adding another {@link Predicate}.
    */
-  DirectionConverter getDirectionConverter();
+  public static class MorePredicateGetter extends Getter {
+    private final Getter original;
+
+    public MorePredicateGetter(Getter original, Predicate<? super UiElement> extraPredicate,
+        String extraDescription) {
+      super(Predicates.and(original.predicate, extraPredicate), extraDescription
+          + original.description);
+      this.original = original;
+    }
 
+    @Override
+    protected UiElement getSentinel(List<? extends UiElement> children) {
+      return original.getSentinel(children);
+    }
+  }
+
+  /**
+   * Returns the first child as the sentinel.
+   */
+  public static final Getter FIRST_CHILD_GETTER =
+      new Getter(Predicates.alwaysTrue(), "FIRST_CHILD") {
+        @Override
+        protected UiElement getSentinel(List<? extends UiElement> children) {
+          return children.isEmpty() ? null : children.get(0);
+        }
+      };
   /**
-   * {@inheritDoc}
-   *
+   * Returns the last child as the sentinel.
+   */
+  public static final Getter LAST_CHILD_GETTER = new Getter(Predicates.alwaysTrue(), "LAST_CHILD") {
+    @Override
+    protected UiElement getSentinel(List<? extends UiElement> children) {
+      return children.isEmpty() ? null : children.get(children.size() - 1);
+    }
+  };
+  /**
+   * Returns the second last child as the sentinel. Useful when the activity
+   * always shows the last child as an anchor (for example a footer).
    * <p>
-   * It is recommended that this method return a description to help debugging.
+   * Sometimes uiautomatorviewer may not show the anchor as the last child, due
+   * to the reordering by layout described in {@link UiElement#getChildren}.
+   * This is not a problem with UiAutomationDriver because it sees the same as
+   * uiautomatorviewer does, but could be a problem with InstrumentationDriver.
+   * </p>
+   */
+  public static final Getter SECOND_LAST_CHILD_GETTER = new Getter(Predicates.alwaysTrue(),
+      "SECOND_LAST_CHILD") {
+    @Override
+    protected UiElement getSentinel(List<? extends UiElement> children) {
+      return children.size() < 2 ? null : children.get(children.size() - 2);
+    }
+  };
+  /**
+   * Returns the second child as the sentinel. Useful when the activity shows a
+   * fixed first child.
    */
-  @Override
-  String toString();
+  public static final Getter SECOND_CHILD_GETTER = new Getter(Predicates.alwaysTrue(),
+      "SECOND_CHILD") {
+    @Override
+    protected UiElement getSentinel(List<? extends UiElement> children) {
+      return children.size() <= 1 ? null : children.get(1);
+    }
+  };
 }
diff --git a/src/com/google/android/droiddriver/scroll/StaticSentinelStrategy.java b/src/com/google/android/droiddriver/scroll/StaticSentinelStrategy.java
index 35e6f29..3393e43 100644
--- a/src/com/google/android/droiddriver/scroll/StaticSentinelStrategy.java
+++ b/src/com/google/android/droiddriver/scroll/StaticSentinelStrategy.java
@@ -34,18 +34,17 @@ import com.google.android.droiddriver.scroll.Direction.PhysicalDirection;
  * This does not work if a child is larger than the physical size of the
  * container.
  */
-public class StaticSentinelStrategy extends AbstractSentinelStrategy {
+public class StaticSentinelStrategy extends BaseSentinelStrategy {
   /**
    * Defaults to FIRST_CHILD_GETTER for backward scrolling, LAST_CHILD_GETTER
    * for forward scrolling, and the standard {@link DirectionConverter}.
    */
-  public StaticSentinelStrategy() {
-    super(FIRST_CHILD_GETTER, LAST_CHILD_GETTER, DirectionConverter.STANDARD_CONVERTER);
-  }
+  public static final StaticSentinelStrategy DEFAULT = new StaticSentinelStrategy(
+      FIRST_CHILD_GETTER, LAST_CHILD_GETTER, DirectionConverter.STANDARD_CONVERTER);
 
-  public StaticSentinelStrategy(GetStrategy backwardGetStrategy, GetStrategy forwardGetStrategy,
+  public StaticSentinelStrategy(Getter backwardGetter, Getter forwardGetter,
       DirectionConverter directionConverter) {
-    super(backwardGetStrategy, forwardGetStrategy, directionConverter);
+    super(backwardGetter, forwardGetter, directionConverter);
   }
 
   @Override
diff --git a/src/com/google/android/droiddriver/scroll/SentinelScroller.java b/src/com/google/android/droiddriver/scroll/StepBasedScroller.java
index 273d6fa..07d7fb6 100644
--- a/src/com/google/android/droiddriver/scroll/SentinelScroller.java
+++ b/src/com/google/android/droiddriver/scroll/StepBasedScroller.java
@@ -37,19 +37,11 @@ import com.google.android.droiddriver.util.Logs;
 /**
  * A {@link Scroller} that looks for the desired item in the currently shown
  * content of the scrollable container, otherwise scrolls the container one step
- * at a time and look again, until we cannot scroll any more. A
- * {@link SentinelStrategy} is used to determine whether more scrolling is
+ * at a time and looks again, until we cannot scroll any more. A
+ * {@link ScrollStepStrategy} is used to determine whether more scrolling is
  * possible.
- * <p>
- * This implementation may not work well with InstrumentationDriver if
- * {@link UiElement#getChildren} returns children in an order different from the
- * Accessibility API. In this case you may try
- * {@link AbstractSentinelStrategy#SECOND_LAST_CHILD_GETTER}.
- * </p>
- * TODO: A {@link Scroller} that directly jumps to the item if an
- * InstrumentationDriver is used.
  */
-public class SentinelScroller implements Scroller {
+public class StepBasedScroller implements Scroller {
 
   private static final SingleKeyAction MOVE_HOME = new SingleKeyAction(KeyEvent.KEYCODE_MOVE_HOME,
       1000L, false);
@@ -57,7 +49,7 @@ public class SentinelScroller implements Scroller {
   private final int maxScrolls;
   private final long perScrollTimeoutMillis;
   private final Axis axis;
-  private final SentinelStrategy sentinelStrategy;
+  private final ScrollStepStrategy scrollStepStrategy;
   private final boolean startFromBeginning;
 
   /**
@@ -72,29 +64,21 @@ public class SentinelScroller implements Scroller {
    *        location and scrolling in both directions. It may not always work,
    *        but when it works, it is faster.
    */
-  public SentinelScroller(int maxScrolls, long perScrollTimeoutMillis, Axis axis,
-      SentinelStrategy sentinelStrategy, boolean startFromBeginning) {
+  public StepBasedScroller(int maxScrolls, long perScrollTimeoutMillis, Axis axis,
+      ScrollStepStrategy scrollStepStrategy, boolean startFromBeginning) {
     this.maxScrolls = maxScrolls;
     this.perScrollTimeoutMillis = perScrollTimeoutMillis;
     this.axis = axis;
-    this.sentinelStrategy = sentinelStrategy;
+    this.scrollStepStrategy = scrollStepStrategy;
     this.startFromBeginning = startFromBeginning;
   }
 
   /**
-   * Constructs with default not startFromBegining.
-   */
-  public SentinelScroller(int maxScrolls, long perScrollTimeoutMillis, Axis axis,
-      SentinelStrategy sentinelStrategy) {
-    this(maxScrolls, perScrollTimeoutMillis, axis, sentinelStrategy, false);
-  }
-
-  /**
    * Constructs with default 100 maxScrolls, 1 second for
    * perScrollTimeoutMillis, vertical axis, not startFromBegining.
    */
-  public SentinelScroller(SentinelStrategy sentinelStrategy) {
-    this(100, 1000L, Axis.VERTICAL, sentinelStrategy, false);
+  public StepBasedScroller(ScrollStepStrategy scrollStepStrategy) {
+    this(100, 1000L, Axis.VERTICAL, scrollStepStrategy, false);
   }
 
   // if scrollBack is true, scrolls back to starting location if not found, so
@@ -113,7 +97,7 @@ public class SentinelScroller implements Scroller {
         return driver.getPoller()
             .pollFor(driver, itemFinder, Poller.EXISTS, perScrollTimeoutMillis);
       } catch (TimeoutException e) {
-        if (i < maxScrolls && !sentinelStrategy.scroll(driver, containerFinder, direction)) {
+        if (i < maxScrolls && !scrollStepStrategy.scroll(driver, containerFinder, direction)) {
           break;
         }
       }
@@ -123,9 +107,10 @@ public class SentinelScroller implements Scroller {
     if (i == maxScrolls) {
       // This is often a program error -- maxScrolls is a safety net; we should
       // have either found itemFinder, or stopped to scroll b/c of reaching the
-      // end. If maxScrolls is reasonably large, sentinelStrategy must be wrong.
-      Logs.logfmt(Log.WARN, exception, "Scrolled %s %d times; sentinelStrategy=%s",
-          containerFinder, maxScrolls, sentinelStrategy);
+      // end. If maxScrolls is reasonably large, ScrollStepStrategy must be
+      // wrong.
+      Logs.logfmt(Log.WARN, exception, "Scrolled %s %d times; ScrollStepStrategy=%s",
+          containerFinder, maxScrolls, scrollStepStrategy);
     }
 
     if (scrollBack) {
@@ -145,7 +130,7 @@ public class SentinelScroller implements Scroller {
   @Override
   public UiElement scrollTo(DroidDriver driver, Finder containerFinder, Finder itemFinder) {
     Logs.call(this, "scrollTo", driver, containerFinder, itemFinder);
-    DirectionConverter converter = sentinelStrategy.getDirectionConverter();
+    DirectionConverter converter = scrollStepStrategy.getDirectionConverter();
     PhysicalDirection backwardDirection = converter.toPhysicalDirection(axis, BACKWARD);
 
     if (startFromBeginning) {
diff --git a/src/com/google/android/droiddriver/uiautomation/UiAutomationElement.java b/src/com/google/android/droiddriver/uiautomation/UiAutomationElement.java
index f80f33d..7fc5056 100644
--- a/src/com/google/android/droiddriver/uiautomation/UiAutomationElement.java
+++ b/src/com/google/android/droiddriver/uiautomation/UiAutomationElement.java
@@ -168,7 +168,7 @@ public class UiAutomationElement extends BaseUiElement {
   }
 
   @Override
-  protected InputInjector getInjector() {
+  public InputInjector getInjector() {
     return context.getInjector();
   }