AlertDialog.Builder完成（）結果NPE

Question

我試圖做一個應用程序，點擊一個列表項目開始進度條顯示下載進度。出於某種原因，列表項目正在停止顯示進度條。這裏的代碼：

final CharSequence[] items = { "View Information", "Lock", "Pin", 
       "Delete", "Ban User", "Ban IP", "Download" }; 

     AlertDialog.Builder builder = new AlertDialog.Builder(this); 
     builder.setTitle("Options"); 
     builder.setItems(items, new DialogInterface.OnClickListener() { 
      public void onClick(DialogInterface dialog, int item) { 
       Toast.makeText(getApplicationContext(), items[item], 
         Toast.LENGTH_SHORT).show(); 
       switch (item) { 
       case 0: 
        Intent i = new Intent(TestActivity.this, ActivityTwo.class); 
        i.putExtra("filename", files.get(position).getFilename()); 
        i.putExtra("orig_filename", files.get(position) 
          .getOriginalFilename()); 
        i.putExtra("date", files.get(position).getDate()); 
        i.putExtra("downloads", files.get(position).getDownloads()); 
        i.putExtra("uploader_ip", files.get(position) 
          .getUploaderIP()); 
        i.putExtra("username", files.get(position).getUsername()); 
        i.putExtra("locked", files.get(position).isLocked()); 
        i.putExtra("pinned", files.get(position).isPinned()); 
        startActivityForResult(i, REQUEST_CODE); 
       case 6: 
        downloadFile(files.get(position).getFilename(), files.get(position).getOriginalFilename()); 
       } 
      } 

     }); 
     AlertDialog alert = builder.create(); 
     alert.show(); 

和三個方法控制進度條。

private ProgressDialog progressDialog; 
    public void startProgress() { 
     progressDialog = new ProgressDialog(TestActivity.this); 
     progressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL); 
     progressDialog.setMessage("Loading..."); 
     progressDialog.setCancelable(false); 
     Log.d("Download", String.valueOf(progressDialog.getMax())); 
     progressDialog.show(); 
    } 

    public void updateProgress(int currentSize, int totalSize) { 
     Log.d("Download", String.valueOf((currentSize/totalSize) * 100)); 
     progressDialog.setProgress(((currentSize/totalSize) * 100)); 
    } 

    public void closeProgress() { 
     progressDialog.hide(); 
    } 

啓動進度條的下載文件。

if(alertDialog != null) { 
       alertDialog.dismiss(); 
      } 
      startProgress(); 

      // now, read through the input buffer and write the contents to the 
      // file 
      while ((bufferLength = inputStream.read(buffer)) > 0) { 
       // add the data in the buffer to the file in the file output 
       // stream (the file on the sd card 
       fileOutput.write(buffer, 0, bufferLength); 
       // add up the size so we know how much is downloaded 
       downloadedSize += bufferLength; 
       // this is where you would do something to report the prgress, 
       // like this maybe 
       updateProgress(downloadedSize, totalSize); 
      } 

      closeProgress(); 

這裏的例外：

11-12 20:17:18.407: E/AndroidRuntime(4728): java.lang.NullPointerException 
11-12 20:17:18.407: E/AndroidRuntime(4728):  at com.evandarwin.android.TestActivity.downloadFile(TestActivity.java:244) 
11-12 20:17:18.407: E/AndroidRuntime(4728):  at com.evandarwin.android.TestActivity$1.onClick(TestActivity.java:143) 
11-12 20:17:18.407: E/AndroidRuntime(4728):  at com.android.internal.app.AlertController$AlertParams$3.onItemClick(AlertController.java:873) 
11-12 20:17:18.407: E/AndroidRuntime(4728):  at android.widget.AdapterView.performItemClick(AdapterView.java:284) 
11-12 20:17:18.407: E/AndroidRuntime(4728):  at android.widget.ListView.performItemClick(ListView.java:3513) 
11-12 20:17:18.407: E/AndroidRuntime(4728):  at android.widget.AbsListView$PerformClick.run(AbsListView.java:1812) 
11-12 20:17:18.407: E/AndroidRuntime(4728):  at android.os.Handler.handleCallback(Handler.java:587) 
11-12 20:17:18.407: E/AndroidRuntime(4728):  at android.os.Handler.dispatchMessage(Handler.java:92) 
11-12 20:17:18.407: E/AndroidRuntime(4728):  at android.os.Looper.loop(Looper.java:130) 
11-12 20:17:18.407: E/AndroidRuntime(4728):  at android.app.ActivityThread.main(ActivityThread.java:3683) 
11-12 20:17:18.407: E/AndroidRuntime(4728):  at java.lang.reflect.Method.invokeNative(Native Method) 
11-12 20:17:18.407: E/AndroidRuntime(4728):  at java.lang.reflect.Method.invoke(Method.java:507) 
11-12 20:17:18.407: E/AndroidRuntime(4728):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:889) 
11-12 20:17:18.407: E/AndroidRuntime(4728):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:647) 
11-12 20:17:18.407: E/AndroidRuntime(4728):  at dalvik.system.NativeStart.main(Native Method) 

Answer 1

你還沒有把完整的信息。它發生在downloadFile()。在case 0末尾添加break可能有助於原因（在case 6的末尾添加break）