| // 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| // The stored position may be out-of-date.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| // The stored position may be out-of-date.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(); |
| } |
| } |
| } |
| |