本节使用系统的示例类VideoView继续SurfaceView类相关内容的讲解，以让大家能更深入理解Android系统中图形绘制基础类的实现原理。也许你会发现无法改变VideoView类的控制方面，我们可以通过重构VideoView类来实现更加个性化的播放器。
下面是VideoView类的相关代码。
Java 代码
public class VideoView extends SurfaceView implements MediaPlayerControl { private String TAG = "VideoView"; // settable by the client private Uri mUri; private int mDuration; // all possible internal states private static final int STATE_ERROR = -1; private static final int STATE_IDLE = 0; private static final int STATE_PREPARING = 1; private static final int STATE_PREPARED = 2; private static final int STATE_PLAYING = 3; private static final int STATE_PAUSED = 4; private static final int STATE_PLAYBACK_COMPLETED = 5; // mCurrentState is a VideoView object's current state. // mTargetState is the state that a method caller intends to reach. // For instance, regardless the VideoView object's current state, // calling pause() intends to bring the object to a target state // of STATE_PAUSED. private int mCurrentState = STATE_IDLE; private int mTargetState = STATE_IDLE; // All the stuff we need for playing and showing a video private SurfaceHolder mSurfaceHolder = null; private MediaPlayer mMediaPlayer = null; private int mVideoWidth; private int mVideoHeight; private int mSurfaceWidth; private int mSurfaceHeight; private MediaController mMediaController; private OnCompletionListener mOnCompletionListener; private MediaPlayer.OnPreparedListener mOnPreparedListener; private int mCurrentBufferPercentage; private OnErrorListener mOnErrorListener; private int mSeekWhenPrepared; // recording the seek position while preparing private boolean mCanPause; private boolean mCanSeekBack; private boolean mCanSeekForward; public VideoView(Context context) { super(context); initVideoView(); } public VideoView(Context context, AttributeSet attrs) { this(context, attrs, 0); initVideoView(); } public VideoView(Context context, AttributeSet attrs, int defStyle) { super(context, attrs, defStyle); initVideoView(); } @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { //Log.i("@@@@", "onMeasure"); int width = getDefaultSize(mVideoWidth, widthMeasureSpec); int height = getDefaultSize(mVideoHeight, heightMeasureSpec); if (mVideoWidth > 0 && mVideoHeight > 0) { if ( mVideoWidth * height > width * mVideoHeight ) { //Log.i("@@@", "image too tall, correcting"); height = width * mVideoHeight / mVideoWidth; } else if ( mVideoWidth * height < width * mVideoHeight ) { //Log.i("@@@", "image too wide, correcting"); width = height * mVideoWidth / mVideoHeight; } else { //Log.i("@@@", "aspect ratio is correct: " + //width+"/"+height+"="+ //mVideoWidth+"/"+mVideoHeight); } } //Log.i("@@@@@@@@@@", "setting size: " + width + 'x' + height); setMeasuredDimension(width, height); } public int resolveAdjustedSize(int desiredSize, int measureSpec) { int result = desiredSize; int specMode = MeasureSpec.getMode(measureSpec); int specSize = MeasureSpec.getSize(measureSpec); switch (specMode) { case MeasureSpec.UNSPECIFIED: result = desiredSize; break; case MeasureSpec.AT_MOST: /* Parent says we can be as big as we want, up to specSize. * Don't be larger than specSize, and don't be larger than * the max size imposed on ourselves. */ result = Math.min(desiredSize, specSize); break; case MeasureSpec.EXACTLY: // No choice. Do what we are told. result = specSize; break; } return result; } private void initVideoView() { mVideoWidth = 0; mVideoHeight = 0; getHolder().addCallback(mSHCallback); getHolder().setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS); setFocusable(true); setFocusableInTouchMode(true); requestFocus(); mCurrentState = STATE_IDLE; mTargetState = STATE_IDLE; } public void setVideoPath(String path) { setVideoURI(Uri.parse(path)); } public void setVideoURI(Uri uri) { mUri = uri; mSeekWhenPrepared = 0; openVideo(); requestLayout(); invalidate(); } public void stopPlayback() { if (mMediaPlayer != null) { mMediaPlayer.stop(); mMediaPlayer.release(); mMediaPlayer = null; mCurrentState = STATE_IDLE; mTargetState = STATE_IDLE; } } private void openVideo() { if (mUri == null || mSurfaceHolder == null) { // not ready for playback just yet, will try again later return; } // Tell the music playback service to pause // TODO: these constants need to be published somewhere in the framework. Intent i = new Intent("com.android.music.musicservicecommand"); i.putExtra("command", "pause"); mContext.sendBroadcast(i); // we shouldn't clear the target state, because somebody might have // called start() previously release(false); try { mMediaPlayer = new MediaPlayer(); mMediaPlayer.setOnPreparedListener(mPreparedListener); mMediaPlayer.setOnVideoSizeChangedListener(mSizeChangedListener); mDuration = -1; mMediaPlayer.setOnCompletionListener(mCompletionListener); mMediaPlayer.setOnErrorListener(mErrorListener); mMediaPlayer.setOnBufferingUpdateListener(mBufferingUpdateListener); mCurrentBufferPercentage = 0; mMediaPlayer.setDataSource(mContext, mUri); mMediaPlayer.setDisplay(mSurfaceHolder); mMediaPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC); mMediaPlayer.setScreenOnWhilePlaying(true); mMediaPlayer.prepareAsync(); // we don't set the target state here either, but preserve the // target state that was there before. mCurrentState = STATE_PREPARING; attachMediaController(); } catch (IOException ex) { Log.w(TAG, "Unable to open content: " + mUri, ex); mCurrentState = STATE_ERROR; mTargetState = STATE_ERROR; mErrorListener.onError(mMediaPlayer, MediaPlayer.MEDIA_ERROR_UNKNOWN, 0); return; } catch (IllegalArgumentException ex) { Log.w(TAG, "Unable to open content: " + mUri, ex); mCurrentState = STATE_ERROR; mTargetState = STATE_ERROR; mErrorListener.onError(mMediaPlayer, MediaPlayer.MEDIA_ERROR_UNKNOWN, 0); return; } } public void setMediaController(MediaController controller) { if (mMediaController != null) { mMediaController.hide(); } mMediaController = controller; attachMediaController(); } private void attachMediaController() { if (mMediaPlayer != null && mMediaController != null) { mMediaController.setMediaPlayer(this); View anchorView = this.getParent() instanceof View ? (View)this.getParent() : this; mMediaController.setAnchorView(anchorView); mMediaController.setEnabled(isInPlaybackState()); } } MediaPlayer.OnVideoSizeChangedListener mSizeChangedListener = new MediaPlayer.OnVideoSizeChangedListener() { public void onVideoSizeChanged(MediaPlayer mp, int width, int height) { mVideoWidth = mp.getVideoWidth(); mVideoHeight = mp.getVideoHeight(); if (mVideoWidth != 0 && mVideoHeight != 0) { getHolder().setFixedSize(mVideoWidth, mVideoHeight); } } }; MediaPlayer.OnPreparedListener mPreparedListener = new MediaPlayer.OnPreparedListener() { public void onPrepared(MediaPlayer mp) { mCurrentState = STATE_PREPARED; // Get the capabilities of the player for this stream Metadata data = mp.getMetadata(MediaPlayer.METADATA_ALL, MediaPlayer.BYPASS_METADATA_FILTER); if (data != null) { mCanPause = !data.has(Metadata.PAUSE_AVAILABLE) || data.getBoolean(Metadata.PAUSE_AVAILABLE); mCanSeekBack = !data.has(Metadata.SEEK_BACKWARD_AVAILABLE) || data.getBoolean(Metadata.SEEK_BACKWARD_AVAILABLE); mCanSeekForward = !data.has(Metadata.SEEK_FORWARD_AVAILABLE) || data.getBoolean(Metadata.SEEK_FORWARD_AVAILABLE); } else { mCanPause = mCanSeekForward = mCanSeekForward = true; } if (mOnPreparedListener != null) { mOnPreparedListener.onPrepared(mMediaPlayer); } if (mMediaController != null) { mMediaController.setEnabled(true); } mVideoWidth = mp.getVideoWidth(); mVideoHeight = mp.getVideoHeight(); int seekToPosition = mSeekWhenPrepared; // mSeekWhenPrepared may be changed after seekTo() call if (seekToPosition != 0) { seekTo(seekToPosition); } if (mVideoWidth != 0 && mVideoHeight != 0) { //Log.i("@@@@", "video size: " + mVideoWidth +"/"+ mVideoHeight); getHolder().setFixedSize(mVideoWidth, mVideoHeight); if (mSurfaceWidth == mVideoWidth && mSurfaceHeight == mVideoHeight) { // We didn't actually change the size (it was already at the size // we need), so we won't get a "surface changed" callback, so // start the video here instead of in the callback. if (mTargetState == STATE_PLAYING) { start(); if (mMediaController != null) { mMediaController.show(); } } else if (!isPlaying() && (seekToPosition != 0 || getCurrentPosition() > 0)) { if (mMediaController != null) { // Show the media controls when we're paused into a video and make 'em stick. mMediaController.show(0); } } } } else { // We don't know the video size yet, but should start anyway. // The video size might be reported to us later. if (mTargetState == STATE_PLAYING) { start(); } } } }; private MediaPlayer.OnCompletionListener mCompletionListener = new MediaPlayer.OnCompletionListener() { public void onCompletion(MediaPlayer mp) { mCurrentState = STATE_PLAYBACK_COMPLETED; mTargetState = STATE_PLAYBACK_COMPLETED; if (mMediaController != null) { mMediaController.hide(); } if (mOnCompletionListener != null) { mOnCompletionListener.onCompletion(mMediaPlayer); } } }; private MediaPlayer.OnErrorListener mErrorListener = new MediaPlayer.OnErrorListener() { public boolean onError(MediaPlayer mp, int framework_err, int impl_err) { Log.d(TAG, "Error: " + framework_err + "," + impl_err); mCurrentState = STATE_ERROR; mTargetState = STATE_ERROR; if (mMediaController != null) { mMediaController.hide(); } /* If an error handler has been supplied, use it and finish. */ if (mOnErrorListener != null) { if (mOnErrorListener.onError(mMediaPlayer, framework_err, impl_err)) { return true; } } /* Otherwise, pop up an error dialog so the user knows that * something bad has happened. Only try and pop up the dialog * if we're attached to a window. When we're going away and no * longer have a window, don't bother showing the user an error. */ if (getWindowToken() != null) { Resources r = mContext.getResources(); int messageId; if (framework_err == MediaPlayer.MEDIA_ERROR_NOT_VALID_FOR_PROGRESSIVE_PLAYBACK) { messageId = com.android.internal.R.string.VideoView_error_text_invalid_progressive_playback; } else { messageId = com.android.internal.R.string.VideoView_error_text_unknown; } new AlertDialog.Builder(mContext) .setTitle(com.android.internal.R.string.VideoView_error_title) .setMessage(messageId) .setPositiveButton(com.android.internal.R.string.VideoView_error_button, new DialogInterface.OnClickListener() { public void onClick(DialogInterface dialog, int whichButton) { /* If we get here, there is no onError listener, so * at least inform them that the video is over. */ if (mOnCompletionListener != null) { mOnCompletionListener.onCompletion(mMediaPlayer); } } }) .setCancelable(false) .show(); } return true; } }; private MediaPlayer.OnBufferingUpdateListener mBufferingUpdateListener = new MediaPlayer.OnBufferingUpdateListener() { public void onBufferingUpdate(MediaPlayer mp, int percent) { mCurrentBufferPercentage = percent; } }; /** * Register a callback to be invoked when the media file * is loaded and ready to go. * * @param l The callback that will be run */ public void setOnPreparedListener(MediaPlayer.OnPreparedListener l) { mOnPreparedListener = l; } /** * Register a callback to be invoked when the end of a media file * has been reached during playback. * * @param l The callback that will be run */ public void setOnCompletionListener(OnCompletionListener l) { mOnCompletionListener = l; } /** * Register a callback to be invoked when an error occurs * during playback or setup. If no listener is specified, * or if the listener returned false, VideoView will inform * the user of any errors. * * @param l The callback that will be run */ public void setOnErrorListener(OnErrorListener l) { mOnErrorListener = l; } SurfaceHolder.Callback mSHCallback = new SurfaceHolder.Callback() { public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) { mSurfaceWidth = w; mSurfaceHeight = h; boolean isValidState = (mTargetState == STATE_PLAYING); boolean hasValidSize = (mVideoWidth == w && mVideoHeight == h); if (mMediaPlayer != null && isValidState && hasValidSize) { if (mSeekWhenPrepared != 0) { seekTo(mSeekWhenPrepared); } start(); if (mMediaController != null) { mMediaController.show(); } } } public void surfaceCreated(SurfaceHolder holder) { mSurfaceHolder = holder; openVideo(); } public void surfaceDestroyed(SurfaceHolder holder) { // after we return from this we can't use the surface any more mSurfaceHolder = null; if (mMediaController != null) mMediaController.hide(); release(true); } }; private void release(boolean cleartargetstate) { if (mMediaPlayer != null) { mMediaPlayer.reset(); mMediaPlayer.release(); mMediaPlayer = null; mCurrentState = STATE_IDLE; if (cleartargetstate) { mTargetState = STATE_IDLE; } } } @Override public boolean onTouchEvent(MotionEvent ev) { if (isInPlaybackState() && mMediaController != null) { toggleMediaControlsVisiblity(); } return false; } @Override public boolean onTrackballEvent(MotionEvent ev) { if (isInPlaybackState() && mMediaController != null) { toggleMediaControlsVisiblity(); } return false; } @Override public boolean onKeyDown(int keyCode, KeyEvent event) { boolean isKeyCodeSupported = keyCode != KeyEvent.KEYCODE_BACK && keyCode != KeyEvent.KEYCODE_VOLUME_UP && keyCode != KeyEvent.KEYCODE_VOLUME_DOWN && keyCode != KeyEvent.KEYCODE_MENU && keyCode != KeyEvent.KEYCODE_CALL && keyCode != KeyEvent.KEYCODE_ENDCALL; if (isInPlaybackState() && isKeyCodeSupported && mMediaController != null) { if (keyCode == KeyEvent.KEYCODE_HEADSETHOOK || keyCode == KeyEvent.KEYCODE_MEDIA_PLAY_PAUSE) { if (mMediaPlayer.isPlaying()) { pause(); mMediaController.show(); } else { start(); mMediaController.hide(); } return true; } else if (keyCode == KeyEvent.KEYCODE_MEDIA_STOP && mMediaPlayer.isPlaying()) { pause(); mMediaController.show(); } else { toggleMediaControlsVisiblity(); } } return super.onKeyDown(keyCode, event); } private void toggleMediaControlsVisiblity() { if (mMediaController.isShowing()) { mMediaController.hide(); } else { mMediaController.show(); } } public void start() { if (isInPlaybackState()) { mMediaPlayer.start(); mCurrentState = STATE_PLAYING; } mTargetState = STATE_PLAYING; } public void pause() { if (isInPlaybackState()) { if (mMediaPlayer.isPlaying()) { mMediaPlayer.pause(); mCurrentState = STATE_PAUSED; } } mTargetState = STATE_PAUSED; } // cache duration as mDuration for faster access public int getDuration() { if (isInPlaybackState()) { if (mDuration > 0) { return mDuration; } mDuration = mMediaPlayer.getDuration(); return mDuration; } mDuration = -1; return mDuration; } public int getCurrentPosition() { if (isInPlaybackState()) { return mMediaPlayer.getCurrentPosition(); } return 0; } public void seekTo(int msec) { if (isInPlaybackState()) { mMediaPlayer.seekTo(msec); mSeekWhenPrepared = 0; } else { mSeekWhenPrepared = msec; } } public boolean isPlaying() { return isInPlaybackState() && mMediaPlayer.isPlaying(); } public int getBufferPercentage() { if (mMediaPlayer != null) { return mCurrentBufferPercentage; } return 0; } private boolean isInPlaybackState() { return (mMediaPlayer != null && mCurrentState != STATE_ERROR && mCurrentState != STATE_IDLE && mCurrentState != STATE_PREPARING); } public boolean canPause() { return mCanPause; } public boolean canSeekBackward() { return mCanSeekBack; } public boolean canSeekForward() { return mCanSeekForward; } }
以上就是对Android VideoView 类的详细介绍，后续继续补充相关知识，谢谢大家对本站的支持！