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。