VideoPlayer 共有三个文件
- video_player.dart （657行）
- VideoPlayerPlugin.java （386行）
- QueuingEventSink.java （82行）
还好，不算太长，先从最短的开始吧：
QueuingEventSink.java
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/**
* And implementation of {@link EventChannel.EventSink} which can wrap an underlying sink.
*
* <p>It delivers messages immediately when downstream is available, but it queues messages before
* the delegate event sink is set with setDelegate.
*
* <p>This class is not thread-safe. All calls must be done on the same thread or synchronized
* externally.
*/
EventChannel.EventSink 的一个实现，用于封装底层通道。此类无法保证线程安全。
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@Override
public void success(Object event) {
enqueue(event);
maybeFlush();
}
此类做的事只有两件，当success 传递event 时，入列，并调用 flush ,而 flush 则是向 delegate 调用 success 方法。为什么要做一个这样的代理层？继续看看下一个 java文件：
VideoPlayerPlugin.java
此文件包含一个插件必须的类 VideoPlayerPlugin 及一个内部类 VideoPlayer。
入口函数：
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public static void registerWith(Registrar registrar) {
final VideoPlayerPlugin plugin = new VideoPlayerPlugin(registrar);
final MethodChannel channel =
new MethodChannel(registrar.messenger(), "flutter.io/videoPlayer");
channel.setMethodCallHandler(plugin);
registrar.addViewDestroyListener(
new PluginRegistry.ViewDestroyListener() {
@Override
public boolean onViewDestroy(FlutterNativeView view) {
plugin.onDestroy();
return false; // We are not interested in assuming ownership of the NativeView.
}
});
}
实例化一个 Plugin 并设置 methodChannel 及监听videDestroy事件（用于视频的销毁？）
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private VideoPlayerPlugin(Registrar registrar) {
this.registrar = registrar;
this.videoPlayers = new HashMap<>();
}
plugin 的构造函数，videoPlayers 表明这个插件需考虑多个player并存的情况。
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@Override
public void onMethodCall(MethodCall call, Result result) {
TextureRegistry textures = registrar.textures();
if (textures == null) {
result.error("no_activity", "video_player plugin requires a foreground activity", null);
return;
}
switch (call.method) {
case "init":
for (VideoPlayer player : videoPlayers.values()) {
player.dispose();
}
videoPlayers.clear();
break;
case "create":
{
TextureRegistry.SurfaceTextureEntry handle = textures.createSurfaceTexture();
EventChannel eventChannel =
new EventChannel(
registrar.messenger(), "flutter.io/videoPlayer/videoEvents" + handle.id());
VideoPlayer player;
if (call.argument("asset") != null) {
String assetLookupKey;
if (call.argument("package") != null) {
assetLookupKey =
registrar.lookupKeyForAsset(
(String) call.argument("asset"), (String) call.argument("package"));
} else {
assetLookupKey = registrar.lookupKeyForAsset((String) call.argument("asset"));
}
player =
new VideoPlayer(
registrar.context(),
eventChannel,
handle,
"asset:///" + assetLookupKey,
result);
videoPlayers.put(handle.id(), player);
} else {
player =
new VideoPlayer(
registrar.context(),
eventChannel,
handle,
(String) call.argument("uri"),
result);
videoPlayers.put(handle.id(), player);
}
break;
}
default:
{
long textureId = ((Number) call.argument("textureId")).longValue();
VideoPlayer player = videoPlayers.get(textureId);
if (player == null) {
result.error(
"Unknown textureId",
"No video player associated with texture id " + textureId,
null);
return;
}
onMethodCall(call, result, textureId, player);
break;
}
}
}
onMethodCall ，dart 端的入口。主要逻辑有三个：
- init : 清除所有player
- create : 根据 id 创建 Texture 及 EventChannel, VideoPlayer 等
-
defalut : 调用另一个 onMethodCall
// “另一个 onMethodCall “ private void onMethodCall(MethodCall call, Result result, long textureId, VideoPlayer player) { switch (call.method) { case “setLooping”: player.setLooping((Boolean) call.argument(“looping”)); result.success(null); break; case “setVolume”: player.setVolume((Double) call.argument(“volume”)); result.success(null); break; case “play”: player.play(); result.success(null); break; case “pause”: player.pause(); result.success(null); break; case “seekTo”: int location = ((Number) call.argument(“location”)).intValue(); player.seekTo(location); result.success(null); break; case “position”: result.success(player.getPosition()); break; case “dispose”: player.dispose(); videoPlayers.remove(textureId); result.success(null); break; default: result.notImplemented(); break; }
这个 onMethodCall 主要把视频创建以外的生命周期函数放在一起。
以上代码都只是一个设置，核心代码要登场了：内部类 VideoPlayer
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private SimpleExoPlayer exoPlayer;
private Surface surface;
private final TextureRegistry.SurfaceTextureEntry textureEntry;
private QueuingEventSink eventSink = new QueuingEventSink();
private final EventChannel eventChannel;
private boolean isInitialized = false;
ExoPlayer 是 google 官方提供的一个Android视频播放器，功能比原生的 MediaPlayer API 要丰富，易于扩展及自定义。
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VideoPlayer(
Context context,
EventChannel eventChannel,
TextureRegistry.SurfaceTextureEntry textureEntry,
String dataSource,
Result result) {
// 设置 ExoPlayer
setupVideoPlayer(eventChannel, textureEntry, result);
}
private void setupVideoPlayer(
EventChannel eventChannel,
TextureRegistry.SurfaceTextureEntry textureEntry,
Result result) {
eventChannel.setStreamHandler(
new EventChannel.StreamHandler() {
@Override
public void onListen(Object o, EventChannel.EventSink sink) {
eventSink.setDelegate(sink);
}
@Override
public void onCancel(Object o) {
eventSink.setDelegate(null); // setDelegate 为 null 可以避免内存泄露？
}
});
surface = new Surface(textureEntry.surfaceTexture());
exoPlayer.setVideoSurface(surface);
setAudioAttributes(exoPlayer);
exoPlayer.addListener(
new DefaultEventListener() {
@Override
public void onPlayerStateChanged(final boolean playWhenReady, final int playbackState) {
super.onPlayerStateChanged(playWhenReady, playbackState);
if (playbackState == Player.STATE_BUFFERING) {
Map<String, Object> event = new HashMap<>();
event.put("event", "bufferingUpdate");
List<Integer> range = Arrays.asList(0, exoPlayer.getBufferedPercentage());
// iOS supports a list of buffered ranges, so here is a list with a single range.
event.put("values", Collections.singletonList(range));
eventSink.success(event);
} else if (playbackState == Player.STATE_READY && !isInitialized) {
isInitialized = true;
sendInitialized();
}
}
@Override
public void onPlayerError(final ExoPlaybackException error) {
super.onPlayerError(error);
if (eventSink != null) {
eventSink.error("VideoError", "Video player had error " + error, null);
}
}
});
Map<String, Object> reply = new HashMap<>();
reply.put("textureId", textureEntry.id());
result.success(reply);
}
@SuppressWarnings("deprecation")
private static void setAudioAttributes(SimpleExoPlayer exoPlayer) {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
exoPlayer.setAudioAttributes(
new AudioAttributes.Builder().setContentType(C.CONTENT_TYPE_MOVIE).build());
} else {
exoPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC);
}
}
void play() {
exoPlayer.setPlayWhenReady(true);
}
void pause() {
exoPlayer.setPlayWhenReady(false);
}
void setLooping(boolean value) {
exoPlayer.setRepeatMode(value ? REPEAT_MODE_ALL : REPEAT_MODE_OFF);
}
void setVolume(double value) {
float bracketedValue = (float) Math.max(0.0, Math.min(1.0, value));
exoPlayer.setVolume(bracketedValue);
}
void seekTo(int location) {
exoPlayer.seekTo(location);
}
long getPosition() {
return exoPlayer.getCurrentPosition();
}
private void sendInitialized() {
if (isInitialized) {
Map<String, Object> event = new HashMap<>();
event.put("event", "initialized");
event.put("duration", exoPlayer.getDuration());
if (exoPlayer.getVideoFormat() != null) {
event.put("width", exoPlayer.getVideoFormat().width);
event.put("height", exoPlayer.getVideoFormat().height);
}
eventSink.success(event);
}
}
void dispose() {
if (isInitialized) {
exoPlayer.stop();
}
textureEntry.release();
eventChannel.setStreamHandler(null);
if (surface != null) {
surface.release();
}
if (exoPlayer != null) {
exoPlayer.release();
}
}
}
以上代码可以看到，从播放到停止，flutter 和 native 之间只是传递了简单的指令，并不存在视频数据的传输 万万没想到——flutter这样外接纹理 ！