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：

1 private void setVolum()
2     {
3         
4         maxVolume = mAudioManager.getStreamMaxVolume(AudioManager.STREAM_MUSIC);
5         volSeekBar.setMax(maxVolume);
6         currentVolume = mAudioManager.getStreamVolume(AudioManager.STREAM_MUSIC);
7         volSeekBar.setProgress(currentVolume);
8         mVolume.setText(currentVolume*100/maxVolume + " ");
9     }

  　　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：

 1 Handler myHandler = new Handler(){
 2         public void handleMessage(Message msg) {  
 3             switch (msg.what) {  
 4             case PROGRESS_CHANGED:  
 5                 setVolum();  
 6                 /*sendEmptyMessageDelayed(PROGRESS_CHANGED, 200);*/
 7                 break;
 8            }
 9         }
10     };
11 
12  class myVolThread implements Runnable {   
13         public void run() {  
14              while (!Thread.currentThread().isInterrupted()) {    
15                      
16                   Message message = new Message();   
17                   message.what =PROGRESS_CHANGED;   
18                   MainActivity.this.myHandler.sendMessage(message);   
19                   try {   
20                        Thread.sleep(100);    
21                   } catch (InterruptedException e) {   
22                        Thread.currentThread().interrupt();   
23                   }   
24              }   
25         }   
26    }

  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();   
                  }   
             }   
        }   
   }   
}