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;

    @Override
    public 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。