android之VideoView和视频播放View的扩展

1.概念及扩展

　　VideoView 是android 系统提供的一个媒体播放显示和控制的控件。其结构层次如下：

　　原型：VideoView extends SurfaceView implements MediaController.MediaPlayerControl

　　类结构：

　　　　　　java.lang.Object
　　　　　　　　↳ android.view.View
　　　　　　　　　　↳ android.view.SurfaceView
　　　　　　　　　　　　↳ android.widget.VideoView

　　通过VideoView 的原型可知：如果构建更为复杂和有特色个性的视频View，需要继承SurfaceView 和实现MediaPlayerControl接口。其中SurfaceView 为显示提供支持，MediaPlayerControl则为媒体控制提供了支持。

2.案例

1)VideoView案例

(我们没有管理MediaPalyer的各种状态，这些状态都让VideoView给封装了，并且，当VideoView创建的时候，MediaPalyer对象将会创建，当VideoView对象销毁的时候，MediaPlayer对象将会释放。)

布局文件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent"android:layout_height="fill_parent">
<VideoView android:id="@+id/video_view" android:layout_width="match_parent" android:layout_height="match_parent"android:layout_centerInParent="true" />
</LinearLayout>

主程序：

public class VideoPlayer extends Activity implements MediaPlayer.OnErrorListener, MediaPlayer.OnCompletionListener {public static final String TAG = "VideoPlayer";private VideoView mVideoView;private Uri mUri;private int mPositionWhenPaused = -1;private MediaController mMediaController;@Overridepublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.main);//Set the screen to landscape.
        this.setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);mVideoView = (VideoView)findViewById(R.id.video_view);//Video file
        mUri = Uri.parse(Environment.getExternalStorageDirectory() + "/1.3gp");//Create media controller，组件可以控制视频的播放，暂停，回复，seek等操作，不需要你实现
        mMediaController = new MediaController(this);mVideoView.setMediaController(mMediaController);}public void onStart() {// Play Video
        mVideoView.setVideoURI(mUri);mVideoView.start();super.onStart();}public void onPause() {// Stop video when the activity is pause.
        mPositionWhenPaused = mVideoView.getCurrentPosition();mVideoView.stopPlayback();super.onPause();}public void onResume() {// Resume video player
        if(mPositionWhenPaused >= 0) {mVideoView.seekTo(mPositionWhenPaused);mPositionWhenPaused = -1;}super.onResume();}public boolean onError(MediaPlayer player, int arg1, int arg2) {return false;}public void onCompletion(MediaPlayer mp) {this.finish();}
}

2)自定义VideoView

和VideoView实现类似，继承了SurfaceView并且实现了MediaPlayerControl。

public class CustomerVideoView extends SurfaceView implements MediaPlayerControl { private static String TAG = "customer.videoplayer"; private boolean pause; private boolean seekBackward; private boolean seekForward; private Uri videoUri; private MediaPlayer mediaPlayer; private Context context; private OnPreparedListener onPreparedListener; private int videoWidth; private int videoHeight; private MediaController mediaController; protected SurfaceHolder surfaceHolder; private Callback surfaceHolderCallback = new SurfaceHolder.Callback() { public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) { } public void surfaceCreated(SurfaceHolder holder) { surfaceHolder = holder; if (mediaPlayer != null) { mediaPlayer.setDisplay(surfaceHolder); resume(); } else { openVideo(); } } public void surfaceDestroyed(SurfaceHolder holder) { surfaceHolder = null; if (mediaController != null) { mediaController.hide(); } release(true); } }; private void release(boolean cleartargetstate) { if (mediaPlayer != null) { mediaPlayer.reset(); mediaPlayer.release(); mediaPlayer = null; } } public void resume() { if (surfaceHolder == null) { return; } if (mediaPlayer != null) { return; } openVideo(); } public CustomerVideoView(Context context, AttributeSet attrs, int defStyle) { super(context, attrs, defStyle); this.context = context; this.initVideoView(); } public CustomerVideoView(Context context, AttributeSet attrs) { super(context, attrs); this.context = context; this.initVideoView(); } public CustomerVideoView(Context context) { super(context); this.context = context; this.initVideoView(); } @Override public boolean canPause() { return this.pause; } @Override public boolean canSeekBackward() { return this.seekBackward; } @Override public boolean canSeekForward() { return this.seekForward; } @Override public int getBufferPercentage() { return 0; } @Override public int getCurrentPosition() { return mediaPlayer!=null?mediaPlayer.getCurrentPosition():0; } @Override public int getDuration() { return mediaPlayer!=null?mediaPlayer.getDuration():0; } @Override public boolean isPlaying() { return false; } @Override public void pause() { } @Override public void seekTo(int mSec) { } @Override public void start() { } public void setVideoURI(Uri uri) { this.videoUri = uri; openVideo(); requestLayout(); invalidate(); } private void openVideo() { this.mediaPlayer = new MediaPlayer(); try { this.mediaPlayer.setDataSource(this.context, this.videoUri); } catch (Exception e) { Log.e(TAG, e.getMessage()); throw new RuntimeException(e); } this.mediaPlayer.prepareAsync(); this.mediaPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC); this.mediaPlayer.setOnPreparedListener(onPreparedListener); attachMediaController(); } private void attachMediaController() { if (mediaPlayer != null && mediaController != null) { mediaController.setMediaPlayer(this); View anchorView = this.getParent() instanceof View ? (View) this .getParent() : this; mediaController.setAnchorView(anchorView); mediaController.setEnabled(true); } } public void setMediaController(MediaController controller) { if (mediaController != null) { mediaController.hide(); } mediaController = controller; attachMediaController(); } public void setOnPreparedListener(OnPreparedListener onPreparedListener) { this.onPreparedListener = onPreparedListener; } @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { int width = getDefaultSize(videoWidth, widthMeasureSpec); int height = getDefaultSize(videoHeight, heightMeasureSpec); if (videoWidth > 0 && videoHeight > 0) { if (videoWidth * height > width * videoHeight) { height = width * videoHeight / videoWidth; } else if (videoWidth * height < width * videoHeight) { width = height * videoWidth / videoHeight; } } Log.i(TAG, "setting size: " + width + ‘x’ + height); setMeasuredDimension(width, height); } private void initVideoView() { videoWidth = 0; videoHeight = 0; getHolder().addCallback(surfaceHolderCallback); getHolder().setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS); setFocusable(true); setFocusableInTouchMode(true); requestFocus(); } 
}

　　一般情况下，android界面的绘制和更新，要交给主ui线程来操作，通过Handler机制。但是播放视频，需要比较优先和实时的改变和绘制界面。android提供了使用单独线程绘制UI的机制，就是SurfaceView。使用SurfaceView，需要实现SurfaceHolder.Callback接口：

• surfaceCreated，在Surface（SurfaceView内部包含一个Surface实例）创建后，会立即调用该方法，可在该方法中做绘制界面相关的初始化工作；
• surfaceChanged，当Surface的状态发生变化，比如大小，会调用该方法，在surfaceCreated方法调用过至少会调用一次该方法；
• surfaceDestroyed，当销毁Surface的时候调用。

　　开发者不能直接操作Surface实例，要通过SurfaceHandler，在SurfaceView中可以通过getHandler方法获取到SurfaceHandler实例。
SurfaceHander有一些类型，用来标识Surface实例界面数据来源，可以通过setType来操作：

• SURFACE_TYPE_NORMAL：RAM缓存的原生数据
• SURFACE_TYPE_HARDWARE：通过DMA，direct memory access，就是直接写屏技术获取到的数据，或者其他硬件加速的数据
• SURFACE_TYPE_GPU：通过GPU加速的数据
• SURFACE_TYPE_PUSH_BUFFERS：标识数据来源于其他对象，比如照相机，比如视频播放服务器（android内部有视频播放的服务器，所有播放视频相当于客户端）

　　CustomerVideoView的构造方法，使用超类的构造方法。都会执行initVideoView()方法用来初始化界面和参数。另外一个主要的内容是openVideo()方法：

• mediaPlayer.prepareAsync()，用来异步准备播放，另外还有个prepare()方法，是同步的，也就是全部下载完毕才能播放，显然，在播放网上视频的时候需要用前者；
• 通过attachMediaController()方法，把控制条附加到播放视频的SurfaceView上，这里实现的不完全，因此还不能使用，仅仅是把MediaPlayerControl实例通过setMediaPlayer方法设置一下，供OnPreparedListener用来得到加载成功的回调，另外供外面代码调用得到视频的时长和当前时长。