// Copyright 2013 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
package org.chromium.android_webview;
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 {
/** Called during predraw if the position of the underlying view has changed. */
public interface Listener {
void onPositionChanged(int positionX, int positionY);
}
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// The stored position may be out-of-date.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// The stored position may be out-of-date.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();
}
}
}