Index: base/android/java/src/org/chromium/base/PositionObserver.java |
diff --git a/base/android/java/src/org/chromium/base/PositionObserver.java b/base/android/java/src/org/chromium/base/PositionObserver.java |
new file mode 100644 |
index 0000000000000000000000000000000000000000..9efe2c49206d82a08961ba1675e54d15c7f6a3f9 |
--- /dev/null |
+++ b/base/android/java/src/org/chromium/base/PositionObserver.java |
@@ -0,0 +1,111 @@ |
+// Copyright (c) 2012 The Chromium Authors. All rights reserved. |
joth
2013/09/27 22:23:20
this yr
cjhopman
2013/10/04 18:07:29
Done.
|
+// Use of this source code is governed by a BSD-style license that can be |
+// found in the LICENSE file. |
+ |
+package org.chromium.base; |
joth
2013/09/27 22:23:20
This is only needed in content/browser so I don't
cjhopman
2013/10/04 18:07:29
Done.
|
+ |
+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 PositionObserver { |
+ public interface Listener { |
+ /** |
+ * Called during predraw if the position of the underlying view has changed. |
+ */ |
+ public void onPositionChanged(int positionX, int positionY); |
+ } |
+ |
+ private View mView; |
+ // Absolute position of the container view relative to its parent window. |
+ private int mPositionX, mPositionY; |
+ |
+ private ArrayList<Listener> mListeners; |
+ private ViewTreeObserver.OnPreDrawListener mPreDrawListener; |
+ |
+ /** |
+ * @param view The view to observe. |
+ */ |
+ public PositionObserver(View view) { |
+ mView = view; |
+ mListeners = new ArrayList<Listener>(); |
+ updatePosition(); |
+ mPreDrawListener = new ViewTreeObserver.OnPreDrawListener() { |
+ @Override |
+ public boolean onPreDraw() { |
+ if (updatePosition()) { |
+ for (Listener l : mListeners) { |
+ l.onPositionChanged(mPositionX, mPositionY); |
+ } |
+ } |
+ 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+ // The stored position may be out-of-date.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. |
joth
2013/09/27 22:23:20
the position will be correct during a frame draw,
cjhopman
2013/10/04 18:07:29
The preDrawListener is only registered on the view
|
+ return getCurrentPosition()[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. |
+ return getCurrentPosition()[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 int[] getCurrentPosition() { |
+ int[] position = new int[2]; |
joth
2013/09/27 22:23:20
this will cause garbage allocations on every frame
cjhopman
2013/10/04 18:07:29
Done.
|
+ mView.getLocationInWindow(position); |
+ return position; |
+ } |
+ |
+ private boolean updatePosition() { |
+ int[] position = getCurrentPosition(); |
+ boolean positionChanged = mPositionX != position[0] || mPositionY != position[1]; |
+ mPositionX = position[0]; |
+ mPositionY = position[1]; |
+ return positionChanged; |
+ } |
+} |
+ |