Decouple MediaSession messages from WebContents (full patch)

content/public/android/java/src/org/chromium/content/browser/MediaSessionImpl.java

+// Copyright 2016 The Chromium Authors. All rights reserved.

[Zhiqiang Zhang (Slow), 2016/10/26 12:50:37]

This is a hybrid of "WebContentsImpl & WebContentsObserverProxy" (Java) for
MediaSession (Java). Used to communicate between native and Java.

+// 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 org.chromium.base.ObserverList;
+import org.chromium.base.annotations.CalledByNative;
+import org.chromium.base.annotations.JNINamespace;
+import org.chromium.content_public.browser.MediaSession;
+import org.chromium.content_public.browser.MediaSessionObserver;
+import org.chromium.content_public.common.MediaMetadata;
+
+/**
+ * The MediaSessionImpl Java wrapper to allow communicating with the native
+ * MediaSessionImpl object.
+ */
+@JNINamespace("content")
+public class MediaSessionImpl extends MediaSession {
+    private long mNativeMediaSessionAndroid;
+
+    private ObserverList<MediaSessionObserver> mObservers;
+    private ObserverList.RewindableIterator<MediaSessionObserver> mObserversIterator;
+
+    @Override
+    public void addObserver(MediaSessionObserver observer) {
+        mObservers.addObserver(observer);
+    }
+
+    @Override
+    public void removeObserver(MediaSessionObserver observer) {
+        mObservers.removeObserver(observer);
+    }
+
+    @Override
+    public ObserverList.RewindableIterator<MediaSessionObserver> getObserversForTesting() {
+        return mObservers.rewindableIterator();
+    }
+
+    @Override
+    public void resume() {
+        nativeResume(mNativeMediaSessionAndroid);
+    }
+
+    @Override
+    public void suspend() {
+        nativeSuspend(mNativeMediaSessionAndroid);
+    }
+
+    @Override
+    public void stop() {
+        nativeStop(mNativeMediaSessionAndroid);
+    }
+
+    @CalledByNative
+    private boolean hasObservers() {
+        return !mObservers.isEmpty();
+    }
+
+    @CalledByNative
+    private void mediaSessionDestroyed() {
+        for (mObserversIterator.rewind(); mObserversIterator.hasNext();) {
+            mObserversIterator.next().mediaSessionDestroyed();
+        }
+    }
+
+    @CalledByNative
+    private void mediaSessionStateChanged(boolean isControllable, boolean isSuspended) {
+        for (mObserversIterator.rewind(); mObserversIterator.hasNext();) {
+            mObserversIterator.next().mediaSessionStateChanged(isControllable, isSuspended);
+        }
+    }
+
+    @CalledByNative
+    private void mediaSessionMetadataChanged(MediaMetadata metadata) {
+        for (mObserversIterator.rewind(); mObserversIterator.hasNext();) {
+            mObserversIterator.next().mediaSessionMetadataChanged(metadata);
+        }
+    }
+
+    @CalledByNative
+    private static MediaSessionImpl create(long nativeMediaSession) {
+        return new MediaSessionImpl(nativeMediaSession);
+    }
+
+    @CalledByNative
+    private void tearDown() {
+        mNativeMediaSessionAndroid = 0;
+        for (mObserversIterator.rewind(); mObserversIterator.hasNext();) {
+            mObserversIterator.next().stopObserving();
+        }
+        mObservers.clear();
+    }
+
+    private MediaSessionImpl(long nativeMediaSession) {
+        mNativeMediaSessionAndroid = nativeMediaSession;
+        mObservers = new ObserverList<MediaSessionObserver>();
+        mObserversIterator = mObservers.rewindableIterator();
+    }
+
+    private native void nativeResume(long nativeMediaSessionAndroid);
+    private native void nativeSuspend(long nativeMediaSessionAndroid);
+    private native void nativeStop(long nativeMediaSessionAndroid);
+}