Implement clearListener() method for PositionObserver to clear all registered listeners when Con

content/public/android/java/src/org/chromium/content/browser/ViewPositionObserver.java

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package org.chromium.content.browser;
 
 import android.view.View;
 import android.view.ViewTreeObserver;
 
-import java.util.ArrayList;
+import org.chromium.base.ObserverList;
 
 /**
  * Used to register listeners that can be notified of changes to the position of a view.
  */
 public class ViewPositionObserver implements PositionObserver {
     private View mView;
     // Absolute position of the container view relative to its parent window.
     private final int[] mPosition = new int[2];
 
-    private final ArrayList<Listener> mListeners;
+    private final ObserverList<Listener> mListeners;

[Yaron, 2014/07/22 19:20:25]

Note that there is slightly more overhead to using ObserverList so it shouldn't
be used arbitrarily.

[wajahat, 2014/07/23 04:24:16]

ok reverting this change

     private ViewTreeObserver.OnPreDrawListener mPreDrawListener;
 
     /**
      * @param view The view to observe.
      */
     public ViewPositionObserver(View view) {
         mView = view;
-        mListeners = new ArrayList<Listener>();
+        mListeners = new ObserverList<Listener>();
         updatePosition();
         mPreDrawListener = new ViewTreeObserver.OnPreDrawListener() {
             @Override
             public boolean onPreDraw() {
                 updatePosition();
                 return true;
             }
         };
     }
 
@@ skipping 15 matching lines @@
         // The stored position may be out-of-date. Get the real current position.
         updatePosition();
         return mPosition[1];
     }
 
     /**
      * Register a listener to be called when the position of the underlying view changes.
      */
     @Override
     public void addListener(Listener listener) {
-        if (mListeners.contains(listener)) return;

[Yaron, 2014/07/22 19:20:25]

This is different than what ObserverList is deisgned for. It ensures that you
can make modifications while iteratring over the list of observers, not that you
don't re-add an observer that's already present.

[wajahat, 2014/07/23 04:24:16]

ok, reverting this change

-
         if (mListeners.isEmpty()) {
             mView.getViewTreeObserver().addOnPreDrawListener(mPreDrawListener);
             updatePosition();
         }
 
-        mListeners.add(listener);
+        mListeners.addObserver(listener);
     }
 
     /**
      * Remove a previously installed listener.
      */
     @Override
     public void removeListener(Listener listener) {
-        if (!mListeners.contains(listener)) return;
-
-        mListeners.remove(listener);
+        mListeners.removeObserver(listener);
 
         if (mListeners.isEmpty()) {
             mView.getViewTreeObserver().removeOnPreDrawListener(mPreDrawListener);
         }
     }
 
     private void notifyListeners() {
-        for (int i = 0; i < mListeners.size(); i++) {
-            mListeners.get(i).onPositionChanged(mPosition[0], mPosition[1]);
+        for (PositionObserver.Listener listener : mListeners) {
+            listener.onPositionChanged(mPosition[0], mPosition[1]);
         }
     }
 
     private void updatePosition() {
         int previousPositionX = mPosition[0];
         int previousPositionY = mPosition[1];
         mView.getLocationInWindow(mPosition);
         if (mPosition[0] != previousPositionX || mPosition[1] != previousPositionY) {
             notifyListeners();
         }
     }
+
+    /**
+     * Clears installed listener(s).
+     */
+    public void clearListener() {
+        mListeners.clear();
+    }
 }