android_webview/java/src/org/chromium/android_webview/AwContentsLifecycleNotifier.java

// Copyright 2015 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.android_webview;

import org.chromium.base.ObserverList;
import org.chromium.base.ThreadUtils;
import org.chromium.base.annotations.CalledByNative;
import org.chromium.base.annotations.JNINamespace;

/**
 * This class is intended to notify observers of the existence native instances of
 * aw_contents. It receives a callback when native aw_contents are created or
 * destroyed. Observers are notified when the first instance is created or the
 * last instance is destroyed.
 */
@JNINamespace("android_webview")
public class AwContentsLifecycleNotifier {

    /**
     * Observer interface to be implemented by deriving webview lifecycle observers.
     */
    public static interface Observer {
        public void onFirstWebViewCreated();
        public void onLastWebViewDestroyed();
    }

    private static final ObserverList<Observer> sLifecycleObservers =
            new ObserverList<Observer>();
    private static int sNumWebViews;

    private AwContentsLifecycleNotifier() {}

    public static void addObserver(Observer observer) {
        sLifecycleObservers.addObserver(observer);
    }

    public static void removeObserver(Observer observer) {
        sLifecycleObservers.removeObserver(observer);
    }

    public static boolean hasWebViewInstances() {
        return sNumWebViews > 0;
    }

    // Called on UI thread.
    @CalledByNative
    private static void onWebViewCreated() {
        ThreadUtils.assertOnUiThread();
        assert sNumWebViews >= 0;
        sNumWebViews++;
        if (sNumWebViews == 1) {
            // first webview created, notify observers.
            for (Observer observer : sLifecycleObservers) {
                observer.onFirstWebViewCreated();
            }
        }
    }

    // Called on UI thread.
    @CalledByNative
    private static void onWebViewDestroyed() {
        ThreadUtils.assertOnUiThread();
        assert sNumWebViews > 0;
        sNumWebViews--;
        if (sNumWebViews == 0) {
            // last webview destroyed, notify observers.
            for (Observer observer : sLifecycleObservers) {
                observer.onLastWebViewDestroyed();
            }
        }
    }
}