AsyncTask在片段恢復時不更新UI

我有一個擴展片段的「HomeFragment」類。一切工作正常，第一次創建片段。但是，當我切換到其他片段並回到此時，UI不會更新。實際上它在TextSwitcher中沒有任何顯示。我使用Log.d檢查了ChangeText線程始終在後臺運行。錯誤在哪裏？AsyncTask在片段恢復時不更新UI

public class HomeFragment extends Fragment { 

    private TextSwitcher mSwitcher; 
    String textToShow[]={"Main HeadLine","Your Message"}; 
    int messageCount=textToShow.length; 
    int currentIndex=-1; 
    private Handler myHandler; 
    ChangeText CT; 

    public HomeFragment(){} 

    @SuppressLint("HandlerLeak") 
    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, 
      Bundle savedInstanceState) { 

     View rootView = inflater.inflate(R.layout.fragment_home, container, false); 

     mSwitcher = (TextSwitcher) rootView.findViewById(R.id.textSwitcher); 
     mSwitcher.setFactory(new ViewFactory() { 

      public View makeView() { 
       // TODO Auto-generated method stub 
       TextView myText = new TextView(getActivity()); 
       myText.setGravity(Gravity.TOP | Gravity.CENTER_HORIZONTAL); 
       myText.setTextSize(36); 
       myText.setTextColor(Color.BLUE); 
       return myText; 
      } 
     }); 

// Declare the in and out animations and initialize them 
Animation in = AnimationUtils.loadAnimation(getActivity(),android.R.anim.slide_in_left); 
Animation out = AnimationUtils.loadAnimation(getActivity(),android.R.anim.slide_out_right); 
     mSwitcher.setInAnimation(in); 
     mSwitcher.setOutAnimation(out); 


     myHandler = new Handler() { 
      public void handleMessage(Message msg) { 
       doUpdate(); 
      } 
     }; 




     CT = new ChangeText(); 
     CT.execute(); 

     return rootView; 
    } 

class ChangeText extends AsyncTask<String, String, String> { 

     @Override 
     protected String doInBackground(String... f_url) { 
      try { 

       while(true) 
       { 
        if (isCancelled()) break; 
        myHandler.sendEmptyMessage(currentIndex); 
        SystemClock.sleep(1500); 
       } 


      } catch (Exception e) { 
       Log.e("VIVEK: ", e.getMessage()); 
      } 

      return null; 
     } 

    } 

private void doUpdate() { 
     currentIndex++; 
     if(currentIndex==messageCount) 
     { 
      currentIndex=0; 
     } 
     Log.d("VIVEK", textToShow[currentIndex]); 
     mSwitcher.setText(textToShow[currentIndex]); 
    } 
}

來源

2014-01-23 gomchikbhoka

在asynctask中添加onPostExecute（）方法並調用它doUpdate（） –

onPostExecute（）應該怎麼做？ – gomchikbhoka

call doUpdate（）我想，如果該方法更新片段，沒有真正閱讀所有代碼：D 檢查示例：http://stackoverflow.com/questions/9671546/asynctask-android-example?rq=1 –