Android中自定义SeekBar来控制音量，并与系统音量键的操作保持同步

下文来自：

http://www.itivy.com/android/archive/2011/7/10/android-set-voice-seekbar.html

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很多音乐播放器界面上都有一个音量seekbar，那么在android里面是如何实现的呢？

首先分析下要解决的问题：

    1.获取媒体播放的音量。

    2.通过seekbar可以增减音量

    3.用户按下音量键增减音量，seekbar保持同步

对于第一个问题：Android系统提供AudioManager类来获得系统audio服务。

对于第二个问题：实现seekBarChangeLIstener里面onProgressChanged方法。

对于第三个问题：用线程来同步更新UI。

设置音量的代码：

private void setVolum()
{
   maxVolume = mAudioManager.getStreamMaxVolume(AudioManager.STREAM_MUSIC);
   volSeekBar.setMax(maxVolume);
   currentVolume = mAudioManager.getStreamVolume(AudioManager.STREAM_MUSIC);
   volSeekBar.setProgress(currentVolume);
   mVolume.setText(currentVolume* 100 /maxVolume + " " );
}

实现seekbar控制音量代码：

OnSeekBarChangeListener seekBarChangeListener = new OnSeekBarChangeListener()
{
    public void onProgressChanged(SeekBar seekBar, int progress,
    boolean fromUser) {
       // TODO Auto-generated method stub
       mAudioManager.setStreamVolume(AudioManager.STREAM_MUSIC, progress, 0 );
    }

    public void onStartTrackingTouch(SeekBar seekBar) {
       // TODO Auto-generated method stub

    }

    public void onStopTrackingTouch(SeekBar seekBar) {
       // TODO Auto-generated method stub

    }

};

线程更新UI代码：

Handler myHandler = new Handler(){
         public void handleMessage(Message msg) {
             switch (msg.what) {
             case PROGRESS_CHANGED:
                 setVolum();
                 /*sendEmptyMessageDelayed(PROGRESS_CHANGED, 200);*/
                 break ;
            }
         }
    };

 class myVolThread implements Runnable {
        public void run() {
             while (!Thread.currentThread().isInterrupted()) {

                  Message message = new Message();
                  message.what =PROGRESS_CHANGED;
                  MainActivity. this .myHandler.sendMessage(message);
                  try {
                       Thread.sleep( 100 );
                  } catch (InterruptedException e) {
                       Thread.currentThread().interrupt();
                  }
             }
        }
   }

最后贴上MainActivity代码：

public class MainActivity extends Activity {

    protected static final int PROGRESS_CHANGED = 0x101 ;
    private SeekBar volSeekBar ;
    private TextView mVolume ;
    private AudioManager mAudioManager;
    private int maxVolume, currentVolume;

    Thread myVolThread = null ;
    Handler myHandler = new Handler(){
        public void handleMessage(Message msg) {
            switch (msg.what) {
            case PROGRESS_CHANGED:
                setVolum();
                /*sendEmptyMessageDelayed(PROGRESS_CHANGED, 200);*/
                break ;
           }
        }
    };
    public void onCreate(Bundle savedInstanceState) {
        super .onCreate(savedInstanceState);
        setContentView(R.layout.main);

        volSeekBar= (SeekBar)findViewById(R.id.volum_seek);
        mVolume = (TextView)findViewById(R.id.volum_val);
        mAudioManager = (AudioManager)getSystemService(Context.AUDIO_SERVICE);

        //setVolum();
        OnSeekBarChangeListener seekBarChangeListener = new OnSeekBarChangeListener()
        {

            public void onProgressChanged(SeekBar seekBar, int progress,
                    boolean fromUser) {
                // TODO Auto-generated method stub
                mAudioManager.setStreamVolume(AudioManager.STREAM_MUSIC, progress, 0 );
            }

            public void onStartTrackingTouch(SeekBar seekBar) {
                // TODO Auto-generated method stub

            }

            public void onStopTrackingTouch(SeekBar seekBar) {
                // TODO Auto-generated method stub

            }

        };

        volSeekBar.setOnSeekBarChangeListener(seekBarChangeListener);
        new Thread( new myVolThread()).start();

    }
    private void setVolum()
    {

        maxVolume = mAudioManager.getStreamMaxVolume(AudioManager.STREAM_MUSIC);
        volSeekBar.setMax(maxVolume);
        currentVolume = mAudioManager.getStreamVolume(AudioManager.STREAM_MUSIC);
        volSeekBar.setProgress(currentVolume);
        mVolume.setText(currentVolume* 100 /maxVolume + " " );
    }

    class myVolThread implements Runnable {
        public void run() {
             while (!Thread.currentThread().isInterrupted()) {

                  Message message = new Message();
                  message.what =PROGRESS_CHANGED;
                  MainActivity. this .myHandler.sendMessage(message);
                  try {
                       Thread.sleep( 100 );
                  } catch (InterruptedException e) {
                       Thread.currentThread().interrupt();
                  }
             }
        }
   }
}

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注：原来我为了保持与 系统按键操作的统一，在Acitity中通过

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        
        switch (keyCode){
        case KeyEvent.KEYCODE_VOLUME_DOWN:
             ddApplication.reSaveMusicVolume();
             break;
        case KeyEvent.KEYCODE_VOLUME_UP:
             ddApplication.reSaveMusicVolume();
             break;
        }
        musicControl.setProgress(ddApplication.getMusicVolume()); // 这一句不起作用啊
        return super.onKeyDown(keyCode, event);
    }

结果发现并不能实现同步的效果，遂找得上篇来作参考！