北京_賽車平臺出租和視頻播放View的擴展
VideoView 是android 系統提供的一個媒體播放顯示和控制的控件。其結構層次如下：
原型：VideoView extends SurfaceView implements MediaController.MediaPlayerControl
類結構：
java.lang.Object
? android.view.View
? android.view.SurfaceView
? android.widget.VideoView
通過VideoView 的原型可知：如果構建更為復雜和有特色個性的視頻View，需要繼承SurfaceView 和實現MediaPlayerControl接口。其中SurfaceView 為顯示提供支持，MediaPlayerControl則為媒體控制提供了支持。
2.案例
1)VideoView案例
(我們沒有管理MediaPalyer的各種狀態，這些狀態都讓VideoView給封裝了，並且，當VideoView創建的時候，MediaPalyer對象將會創建，當VideoView對象銷毀的時候，MediaPlayer對象將會釋放。)
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"
<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 {
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，組件可以控制視頻的播放，暫停，回復，seek等操作，不需要你實現
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)自定義VideoView
和VideoView實現類似，繼承了SurfaceView並且實現了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();
}
}
一般情況下，android界面的繪制和更新，要交給主ui線程來操作，通過Handler機制。但是播放視頻，需要比較優先和實時的改變和繪制界面。android提供了使用單獨線程繪制UI的機制，就是SurfaceView。使用SurfaceView，需要實現SurfaceHolder.Callback接口：
surfaceCreated，在Surface（SurfaceView內部包含一個Surface實例）創建後，會立即調用該方法，可在該方法中做繪制界面相關的初始化工作；
surfaceChanged，當Surface的狀態發生變化，比如大小，會調用該方法，在surfaceCreated方法調用過至少會調用一次該方法；
surfaceDestroyed，當銷毀Surface的時候調用。 開發者不能直接操作Surface實例，要通過SurfaceHandler，在SurfaceView中可以通過getHandler方法獲取到SurfaceHandler實例。
SurfaceHander有一些類型，用來標識Surface實例界面數據來源，可以通過setType來操作：
SURFACE_TYPE_NORMAL：RAM緩存的原生數據
SURFACE_TYPE_HARDWARE：通過DMA，direct memory access，就是直接寫屏技術獲取到的數據，或者其他硬件加速的數據
SURFACE_TYPE_GPU：通過GPU加速的數據
SURFACE_TYPE_PUSH_BUFFERS：標識數據來源於其他對象，比如照相機，比如視頻播放服務器（android內部有視頻播放的服務器，所有播放視頻相當於客戶端）CustomerVideoView的構造方法，使用超類的構造方法。都會執行initVideoView()方法用來初始化界面和參數。另外一個主要的內容是openVideo()方法：
mediaPlayer.prepareAsync()，用來異步準備播放，另外還有個prepare()方法，是同步的，也就是全部下載完畢才能播放，顯然，在播放網上視頻的時候需要用前者；
通過attachMediaController()方法，把控制條附加到播放視頻的SurfaceView上，這裏實現的不完全，因此還不能使用，僅僅是把MediaPlayerControl實例通過setMediaPlayer方法設置一下，供OnPreparedListener用來得到加載成功的回調，另外供外面代碼調用得到視頻的時長和當前時長。北京_賽車平臺出租和視頻播放View的擴展