Android VideoView类实例讲解

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 clientprivate Uri mUri;private int mDuration; // all possible internal statesprivate 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 videoprivate 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 preparingprivate booleanmCanPause;private booleanmCanSeekBack;private booleanmCanSeekForward; 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（）;} @Overrideprotected 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 laterreturn; } // 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 streamMetadata 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（） callif （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 moremSurfaceHolder = 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;} }} @Overridepublic boolean onTouchEvent（MotionEvent ev） { if （isInPlaybackState（） && mMediaController ！= null） {toggleMediaControlsVisiblity（）; } return false;}@Overridepublic boolean onTrackballEvent（MotionEvent ev） { if （isInPlaybackState（） && mMediaController ！= null） {toggleMediaControlsVisiblity（）; } return false;}@Overridepublic 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 accesspublic 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！