取消的Android

Question

的AsyncTask類我有兩個按鈕。第一個啓動mediaplayer和第二個取消它： mediaplayer是在AsyncTask，我用（線程 - 時間）重複它 我需要mediaplayer播放，直到用戶按下取消 當我開始運行時和我按取消它停止（當我不出去的頁面佈局 - ）

private DoSomething doSomething; 
    @Override 
protected void onCreate(Bundle savedInstanceState) { 
super.onCreate(savedInstanceState); 
setContentView(R.layout.first); 
final MediaPlayer mp; 
mp=MediaPlayer.create(this,R.raw.ab); 

//=================================================== 
    final Button first=(Button)findViewById(R.id.button1); 
    final Button second=(Button)findViewById(R.id.button2); 
    first.setOnClickListener(new OnClickListener() { 

     public void onClick(View arg0) { 
      //start your asynctask 
      if(doSomething == null || doSomething.isCancelled()){ 
      doSomething = new DoSomething(); 
       doSomething = (DoSomething) doSomething.execute(); 
      } } 
    }); 

    second.setOnClickListener(new OnClickListener() { 

     public void onClick(View arg0) { 
    doSomething.cancel(true); 

     } });} 

問題：當我走出去的佈局，並返回到取消的AsyncTask有aproblem在

doSomething.cancel(true); 

因爲空指針的doSomething看到asyntask不運行，而它運行

我用Status g=doSomething.getStatus(); 還在等待沒有運行

class DoSomething extends AsyncTask<Void, Void, Void>{ 

    @Override 
    protected Void doInBackground(Void... params) { 

     while(true){ 
      if(isCancelled()){ 
       break; 
      } 
      final MediaPlayer mp; 
      mp=MediaPlayer.create(getBaseContext(),R.raw.ab); 


         mp.start(); 
         mp.setOnCompletionListener(new OnCompletionListener() { 

          public void onCompletion(MediaPlayer mp) { 
           mp.release(); 
          } 
         }); 

       try { 
        Thread.sleep(8 * 1000); 
       } catch (InterruptedException e) { 
        // TODO Auto-generated catch block 
        e.printStackTrace() }} 
     return null; 
    }} 

Answer 1

最簡單的方法來解決你的問題是改變你的第二擊

second.setOnClickListener(new OnClickListener() { 

     public void onClick(View arg0) { 
      if(doSomething != null && !doSomething.isCancelled()){ 
       doSomething.cancel(true); 
     } 
    }) 
;