1 files changed, 70 insertions, 5 deletions

diff --git a/android/arch/paging/NullPaddedList.java b/android/arch/paging/NullPaddedList.java
index c7b0b231..43000302 100644
--- a/android/arch/paging/NullPaddedList.java
+++ b/android/arch/paging/NullPaddedList.java
@@ -16,9 +16,11 @@
 
 package android.arch.paging;
 
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.support.annotation.RestrictTo;
 
-import java.util.AbstractList;
+import java.util.ArrayList;
 import java.util.List;
 
 /**
@@ -29,11 +31,18 @@ import java.util.List;
  * @hide
  */
 @RestrictTo(RestrictTo.Scope.LIBRARY_GROUP)
-public class NullPaddedList<Type> extends AbstractList<Type> {
+public class NullPaddedList<Type> extends PagedList<Type> {
     List<Type> mList;
-    private int mTrailingNullCount;
-    private int mLeadingNullCount;
-    private int mPositionOffset;
+    int mTrailingNullCount;
+    int mLeadingNullCount;
+    int mPositionOffset;
+
+    // track the items prepended/appended since the PagedList was initialized
+    int mNumberPrepended;
+    int mNumberAppended;
+
+    NullPaddedList() {
+    }
 
     @Override
     public String toString() {
@@ -82,6 +91,20 @@ public class NullPaddedList<Type> extends AbstractList<Type> {
         mPositionOffset = positionOffset;
     }
 
+    /**
+     * Create a copy of the passed NullPaddedList.
+     *
+     * @param other Other list to copy.
+     */
+    NullPaddedList(NullPaddedList<Type> other) {
+        mLeadingNullCount = other.getLeadingNullCount();
+        mList = other.isImmutable() ? other.mList : new ArrayList<>(other.mList);
+        mTrailingNullCount = other.getTrailingNullCount();
+
+        mNumberPrepended = other.getNumberPrepended();
+        mNumberAppended = other.getNumberAppended();
+    }
+
     // --------------- PagedList API ---------------
 
     @Override
@@ -101,12 +124,46 @@ public class NullPaddedList<Type> extends AbstractList<Type> {
     }
 
     @Override
+    public void loadAround(int index) {
+        // do nothing - immutable, so no fetching will be done
+    }
+
+    @Override
     public final int size() {
         return getLoadedCount() + getLeadingNullCount() + getTrailingNullCount();
     }
 
+    public boolean isImmutable() {
+        return true;
+    }
+
+    @Override
+    public PagedList<Type> snapshot() {
+        if (isImmutable()) {
+            return this;
+        }
+        return new NullPaddedList<>(this);
+    }
+
+    @Override
+    boolean isContiguous() {
+        return true;
+    }
+
+    @Override
+    public void addWeakCallback(@Nullable PagedList<Type> previousSnapshot,
+            @NonNull Callback callback) {
+        // no op, immutable
+    }
+
+    @Override
+    public void removeWeakCallback(Callback callback) {
+        // no op, immutable
+    }
+
     // --------------- Contiguous API ---------------
 
+    @Override
     public int getPositionOffset() {
         return mPositionOffset;
     }
@@ -137,4 +194,12 @@ public class NullPaddedList<Type> extends AbstractList<Type> {
     public int getTrailingNullCount() {
         return mTrailingNullCount;
     }
+
+    int getNumberPrepended() {
+        return mNumberPrepended;
+    }
+
+    int getNumberAppended() {
+        return mNumberAppended;
+    }
 }