Index: content/public/android/java/src/org/chromium/content/browser/ViewPositionObserver.java |
diff --git a/content/public/android/java/src/org/chromium/content/browser/ViewPositionObserver.java b/content/public/android/java/src/org/chromium/content/browser/ViewPositionObserver.java |
new file mode 100644 |
index 0000000000000000000000000000000000000000..55de7c4ad73eda7bfb779a2960ec99d58df31575 |
--- /dev/null |
+++ b/content/public/android/java/src/org/chromium/content/browser/ViewPositionObserver.java |
@@ -0,0 +1,99 @@ |
+// 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; |
+ |
+/** |
+ * 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 ViewTreeObserver.OnPreDrawListener mPreDrawListener; |
+ |
+ /** |
+ * @param view The view to observe. |
+ */ |
+ public ViewPositionObserver(View view) { |
+ mView = view; |
+ mListeners = new ArrayList<Listener>(); |
+ updatePosition(); |
+ mPreDrawListener = new ViewTreeObserver.OnPreDrawListener() { |
+ @Override |
+ public boolean onPreDraw() { |
+ updatePosition(); |
+ return true; |
+ } |
+ }; |
+ } |
+ |
+ /** |
+ * @return The current x position of the observed view. |
+ */ |
+ public int getPositionX() { |
+ // The stored position may be out-of-date. Get the real current position. |
+ updatePosition(); |
+ return mPosition[0]; |
+ } |
+ |
+ /** |
+ * @return The current y position of the observed view. |
+ */ |
+ public int getPositionY() { |
+ // The stored position may be out-of-date.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. |
+ */ |
+ public void addListener(Listener listener) { |
+ if (mListeners.contains(listener)) return; |
+ |
+ if (mListeners.isEmpty()) { |
+ mView.getViewTreeObserver().addOnPreDrawListener(mPreDrawListener); |
+ updatePosition(); |
+ } |
+ |
+ mListeners.add(listener); |
+ } |
+ |
+ /** |
+ * Remove a previously installed listener. |
+ */ |
+ public void removeListener(Listener listener) { |
+ if (!mListeners.contains(listener)) return; |
+ |
+ mListeners.remove(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]); |
+ } |
+ } |
+ |
+ private void updatePosition() { |
+ int previousPositionX = mPosition[0]; |
+ int previousPositionY = mPosition[1]; |
+ mView.getLocationInWindow(mPosition); |
+ if (mPosition[0] != previousPositionX || mPosition[1] != previousPositionY) { |
+ notifyListeners(); |
+ } |
+ } |
+} |
+ |