异步任务下载如果没有连接抛出空指针异常

Question

先生，我试图处理消息，如果没有互联网连接。但是，如果有任何网络连接，我仍然继续下载时发生空异常错误。首先，它显示网络连接错误的消息，但是当我按下时，会弹出异常错误消息。当我们处理这个案子时我们应该进一步处理什么？

timer = new Timer(); 
    boolean isOnline = WebServiceHandler.isOnline(this); 
    if (isOnline) { 
     startDownloadTask(); 
    task = new TimerTask() { 

      @Override 
      public void run() { 
       // TODO Auto-generated method stub 
       int progress = downloadProgressBar.getProgress(); 
       notification.contentView.setProgressBar(R.id.pb, downloadProgressBar.getMax(), progress, false); 
       nm.notify(notificationID, notification); 
      } 
     }; 

     timer.schedule(task, 10, 500); 

    } else { 
     connectionErrorDialog.show(); 
     onDestroy(); 


    } 

}  




@Override 
public void stopDownloadTask() { 
    downloadGoodListTask.cancel(true); 
    downloadGoodListTask.setActivityIsRunning(false); 
    downloadGoodListTask = null; 

} 


protected void onDestroy() { 
    super.onDestroy(); 
    Log.i("Download Activity", "starting to destroy"); 
    //timer.cancel(); 


    wheelProgressBar.destroyDrawingCache(); 
    downloadProgressBar.destroyDrawingCache(); 
    finishDialog.dismiss(); 
    connectionErrorDialog.dismiss(); 

    downloadProgressBar = null; 
    wheelProgressBar = null; 
    progressTextView = null; 
    downloadingTextView = null; 
    finishDialog = null; 
    connectionErrorDialog = null;   
    //timer = null;  
    nm.cancel(notificationID); 

    nm = null; 
    notification = null; 
    /*downloadTask.cancel(true); 
    downloadTask.activityIsRunning = false; 
    downloadTask = null;*/ 
    stopDownloadTask(); 
    timer.cancel();   
    System.gc(); 

    Log.i("Download Activity", "destroyed"); 
} 


@Override 
public void stopDownloadTask() { 
    downloadGoodListTask.cancel(true); 
    downloadGoodListTask.setActivityIsRunning(false); 
    downloadGoodListTask = null; 

} 

Answer 1

不从UI线程外部访问Android UI工具包。使用runOnUIThread方法，将消息发送到Handler或使用AsyncTask。

Answer 2

例外是因为downloadGoodListTask为null。要么你应该初始化某个值，要么在stopDownloadTask（）中处理异常。