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[操作系统]Android SurfaceView的生命周期

本文利用SurfaceView来实现视频的播放

本文地址:http://www.cnblogs.com/wuyudong/p/5851156.html,转载请注明源地址。

在main.

<SurfaceView android:layout_width="fill_parent" android:layout_height="240dip" android:id="@+id/surfaceView" />

项目布局设计:

<LinearLayout ="http://schemas.android.com/apk/res/android"  ="http://schemas.android.com/tools"  android:layout_width="match_parent"  android:layout_height="match_parent"  android:orientation="vertical"  tools:context=".MainActivity" >  <EditText    android:id="@+id/et_path"    android:layout_width="fill_parent"    android:layout_height="wrap_content"    android:hint="请输入视频文件的路径" />  <LinearLayout    android:layout_width="fill_parent"    android:layout_height="wrap_content"    android:orientation="horizontal" >    <Button      android:id="@+id/bt_play"      android:layout_width="0dip"      android:layout_height="wrap_content"      android:layout_weight="1"      android:text="播放" />    <Button      android:id="@+id/bt_pause"      android:layout_width="0dip"      android:layout_height="wrap_content"      android:layout_weight="1"      android:text="暂停" />    <Button      android:id="@+id/bt_replay"      android:layout_width="0dip"      android:layout_height="wrap_content"      android:layout_weight="1"      android:text="重播" />    <Button      android:id="@+id/bt_stop"      android:layout_width="0dip"      android:layout_height="wrap_content"      android:layout_weight="1"      android:text="停止" />  </LinearLayout>    <SurfaceView     android:id="@+id/sv"    android:layout_width="fill_parent"    android:layout_height="fill_parent"    /></LinearLayout>

大部分代码和《Android 多媒体播放API简介》中的完全一样,修改一点点代码即可:

public class MainActivity extends Activity implements OnClickListener {  private EditText et_path;  private Button bt_play, bt_replay, bt_pause, bt_stop;  private SurfaceView sv;  private MediaPlayer mediaPlayer;  @Override  protected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);        sv = (SurfaceView)findViewById(R.id.sv);    et_path = (EditText) findViewById(R.id.et_path);    bt_play = (Button) findViewById(R.id.bt_play);    bt_replay = (Button) findViewById(R.id.bt_replay);    bt_pause = (Button) findViewById(R.id.bt_pause);    bt_stop = (Button) findViewById(R.id.bt_stop);    bt_pause.setOnClickListener(this);    bt_play.setOnClickListener(this);    bt_replay.setOnClickListener(this);    bt_stop.setOnClickListener(this);  }  @Override  public void onClick(View v) {    switch (v.getId()) {    case R.id.bt_play:      play();      break;    case R.id.bt_replay:      replay();      break;    case R.id.bt_stop:      stop();      break;    case R.id.bt_pause:      pause();      break;    default:      break;    }  }  /**   * 暂停音乐   */  private void pause() {    if ("继续".equals(bt_pause.getText().toString().trim())) {      mediaPlayer.start();      bt_pause.setText("暂停");      return;    }    if (mediaPlayer != null && mediaPlayer.isPlaying()) {      mediaPlayer.pause();      bt_pause.setText("继续");      return;    }  }  /**   * 重新播放   */  private void replay() {    if (mediaPlayer != null && mediaPlayer.isPlaying()) {      mediaPlayer.seekTo(0);      return;    }    play();  }  /**   * 停止播放音乐   */  private void stop() {    if (mediaPlayer != null && mediaPlayer.isPlaying()) {      mediaPlayer.stop();      mediaPlayer.release(); // 记得释放资源      mediaPlayer = null;      bt_play.setEnabled(true);    }  }  /**   * 播放音乐   */  private void play() {    String path = et_path.getText().toString().trim();    File file = new File(path);    if (file.exists() && file.length() > 0) {      try {        mediaPlayer = new MediaPlayer();        mediaPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC);                /* 设置Video影片以SurfaceHolder播放 */        mediaPlayer.setDisplay(sv.getHolder());                mediaPlayer.setDataSource(path);        mediaPlayer.prepare(); // might take long! (for buffering, etc)        mediaPlayer.start();        mediaPlayer.setOnCompletionListener(new OnCompletionListener() {          @Override          public void onCompletion(MediaPlayer mp) {            bt_play.setEnabled(true);          }        } );                bt_play.setEnabled(false);      } catch (Exception e) {        Toast.makeText(this, "播放失败", 0).show();        e.printStackTrace();      }    } else {      Toast.makeText(this, "文件不存在", 0).show();    }  }}

运行项目效果如下:

但是上面的代码有点问题,那就是当点击home或返回屏幕主界面后,在回到播放页面,视频黑屏

原因:

SurfaceView内部维护双缓冲,消耗内存资源

如果发现当前SurfaceView 用户可见的时候,创建SurfaceView的holder

如果SurfaceView变成用户不可见的时候  销毁SurfaceView的holder

为了观察SurfaceView的生命周期,可以添加下面的代码进行打印追踪:

  sv.getHolder().addCallback(new Callback() {            @Override      public void surfaceDestroyed(SurfaceHolder holder) {        System.out.println("holder被销毁了");      }            @Override      public void surfaceCreated(SurfaceHolder holder) {        System.out.println("holder被创建了");              }            @Override      public void surfaceChanged(SurfaceHolder holder, int format, int width,          int height) {        System.out.println("holder的大小变化了");      }    });  }

logcat中打印下面的信息:

09-07 11:36:34.613: I/System.out(28858): holder被创建了
09-07 11:36:34.623: I/System.out(28858): holder的大小变化了

返回主界面

09-07 11:39:08.245: I/System.out(28858): holder被销毁了

再次回到视频界面

09-07 11:39:39.405: I/System.out(28858): holder被创建了
09-07 11:39:39.405: I/System.out(28858): holder的大小变化了

可以看到,每次回到视频界面,holder都会被重新创建

修改后的代码如下:

public class MainActivity extends Activity implements OnClickListener {  private EditText et_path;  private Button bt_play, bt_replay, bt_pause, bt_stop;  private SurfaceView sv;  private MediaPlayer mediaPlayer;  private int currentPosition;  @Override  protected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);    sv = (SurfaceView) findViewById(R.id.sv);    et_path = (EditText) findViewById(R.id.et_path);    bt_play = (Button) findViewById(R.id.bt_play);    bt_replay = (Button) findViewById(R.id.bt_replay);    bt_pause = (Button) findViewById(R.id.bt_pause);    bt_stop = (Button) findViewById(R.id.bt_stop);    bt_pause.setOnClickListener(this);    bt_play.setOnClickListener(this);    bt_replay.setOnClickListener(this);    bt_stop.setOnClickListener(this);    sv.getHolder().addCallback(new Callback() {      @Override      public void surfaceDestroyed(SurfaceHolder holder) {        System.out.println("holder被销毁了");        if (mediaPlayer != null && mediaPlayer.isPlaying()) {          currentPosition = mediaPlayer.getCurrentPosition();          stop();        }      }      @Override      public void surfaceCreated(SurfaceHolder holder) {        System.out.println("holder被创建了");        if (currentPosition > 0) {          play(currentPosition);        }      }      @Override      public void surfaceChanged(SurfaceHolder holder, int format,          int width, int height) {        System.out.println("holder的大小变化了");      }    });  }  @Override  public void onClick(View v) {    switch (v.getId()) {    case R.id.bt_play:      play(0);      break;    case R.id.bt_replay:      replay();      break;    case R.id.bt_stop:      stop();      break;    case R.id.bt_pause:      pause();      break;    default:      break;    }  }  /**   * 暂停音乐   */  private void pause() {    if ("继续".equals(bt_pause.getText().toString().trim())) {      mediaPlayer.start();      bt_pause.setText("暂停");      return;    }    if (mediaPlayer != null && mediaPlayer.isPlaying()) {      mediaPlayer.pause();      bt_pause.setText("继续");      return;    }  }  /**   * 重新播放   */  private void replay() {    if (mediaPlayer != null && mediaPlayer.isPlaying()) {      mediaPlayer.seekTo(0);      return;    }    play(0);  }  /**   * 停止播放音乐   */  private void stop() {    if (mediaPlayer != null && mediaPlayer.isPlaying()) {      mediaPlayer.stop();      mediaPlayer.release(); // 记得释放资源      mediaPlayer = null;      bt_play.setEnabled(true);    }  }  /**   * 播放音乐   */  private void play(final int currentPosition) {    String path = et_path.getText().toString().trim();    File file = new File(path);    if (file.exists() && file.length() > 0) {      try {        mediaPlayer = new MediaPlayer();        mediaPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC);        /* 设置Video影片以SurfaceHolder播放 */        mediaPlayer.setDisplay(sv.getHolder());        mediaPlayer.setDataSource(path);        mediaPlayer.prepare(); // might take long! (for buffering, etc)        mediaPlayer.start();        mediaPlayer.setOnPreparedListener(new OnPreparedListener() {                    @Override          public void onPrepared(MediaPlayer mp) {            mediaPlayer.seekTo(currentPosition);                      }        });        mediaPlayer.setOnCompletionListener(new OnCompletionListener() {          @Override          public void onCompletion(MediaPlayer mp) {            bt_play.setEnabled(true);          }        });        bt_play.setEnabled(false);      } catch (Exception e) {        Toast.makeText(this, "播放失败", 0).show();        e.printStackTrace();      }    } else {      Toast.makeText(this, "文件不存在", 0).show();    }  }}