更新片段內Textview時的空指針

Question

我正在用兩個片段寫一個應用程序。第一個片段將文本信息發送到創建這兩個片段的活動。這工作完美。我的第二個片段與第一個片段同時創建。第二個片段在其xml佈局中包含一個textview。我的主要活動應該將基於文本的數據傳遞給第二個片段並顯示文本。問題是當文本到達第二個片段方法時，textview alwasy返回一個空指針。

//This is the main methods creation of the fragment  
try { 
    //message frag on bottom 
    FragmentManager fM = getFragmentManager(); 
    FragmentTransaction fTrans = fM.beginTransaction(); 
    messFrag = new DisplayMessageFragment(); 
    fTrans.add(R.id.BottomDisplayFragment, messFrag,"MESSAGE_FRAGMENT"); 
    fTrans.commit(); 
} catch(Exception e) { 
    e.printStackTrace(); 
} 

//this is whe main methods call the fragments text view updating method 
@Override 
public void getDisplayWindowMessage_StartFrag(String message) { 
    getFragmentManager().findFragmentByTag("MESSAGE_FRAGMENT"); 
    messFrag.setMessage(message); 
} 

//This is my fragment class   
public class DisplayMessageFragment extends Fragment { 
    TextView displayedMessage; 
    View view ; 


    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     // TODO Auto-generated method stub 
     super.onCreate(savedInstanceState); 

    } 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, 
          Bundle savedInstanceState) { 
     // TODO Auto-generated method stub 
     view = inflater.inflate(R.layout.displaymess_frag,container, false); 
     displayedMessage = (TextView) view.findViewById(R.id.MessageDisplay); 

     return view; 
    } 

    public void setMessage(String newMessage){ 
     //displayedMessage=(TextView) view.findViewById(R.id.MessageDisplay); 
     displayedMessage = (TextView) getView().findViewById(R.id.MessageDisplay); 
     displayedMessage.setText(newMessage); 
    } 
} 

堆棧跟蹤：

java.lang.NullPointerException 
12-26 02:06:14.505: E/AndroidRuntime(710): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956) 
12-26 02:06:14.505: E/AndroidRuntime(710): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981) 
12-26 02:06:14.505: E/AndroidRuntime(710): at android.app.ActivityThread.access$600(ActivityThread.java:123) 
12-26 02:06:14.505: E/AndroidRuntime(710): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147) 
12-26 02:06:14.505: E/AndroidRuntime(710): at android.os.Handler.dispatchMessage(Handler.java:99) 
12-26 02:06:14.505: E/AndroidRuntime(710): at android.os.Looper.loop(Looper.java:137) 
12-26 02:06:14.505: E/AndroidRuntime(710): at android.app.ActivityThread.main(ActivityThread.java:4424) 
12-26 02:06:14.505: E/AndroidRuntime(710): at java.lang.reflect.Method.invokeNative(Native Method) 
12-26 02:06:14.505: E/AndroidRuntime(710): at java.lang.reflect.Method.invoke(Method.java:511) 
12-26 02:06:14.505: E/AndroidRuntime(710): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) 
12-26 02:06:14.505: E/AndroidRuntime(710): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) 
12-26 02:06:14.505: E/AndroidRuntime(710): at dalvik.system.NativeStart.main(Native Method) 
12-26 02:06:14.505: E/AndroidRuntime(710): Caused by: java.lang.NullPointerException 
12-26 02:06:14.505: E/AndroidRuntime(710): at .DisplayMessageFragment.setMessage(DisplayMessageFragment.java:38) 
12-26 02:06:14.505: E/AndroidRuntime(710): at .Schduler_Activity.getDisplayWindowMessage_StartFrag(Schduler_Activity.java:79) 
12-26 02:06:14.505: E/AndroidRuntime(710): at 
StartFragment.onCreateView(StartFragment.java:31) 
12-26 02:06:14.505: E/AndroidRuntime(710): at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:828) 
12-26 02:06:14.505: E/AndroidRuntime(710): at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1032) 
12-26 02:06:14.505: E/AndroidRuntime(710): at android.app.BackStackRecord.run(BackStackRecord.java:622) 
12-26 02:06:14.505: E/AndroidRuntime(710): at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1382) 
12-26 02:06:14.505: E/AndroidRuntime(710): at android.app.Activity.performStart(Activity.java:4474) 
12-26 02:06:14.505: E/AndroidRuntime(710): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1929) 
12-26 02:06:14.505: E/AndroidRuntime(710): ... 11 more 

Answer 1

我發現我的錯誤。我試圖在第一個片段回調期間調用第二個片段，因爲片段不能直接通信，所以它會拋出NPE。

Answer 2

爲什麼你想重新設置displayedMessage VAR？您將其設置爲onCreateView，並將其作爲類變量，因此當您調用serMessage方法時，它應該仍然存在。

只需將findViewById放入setMesage方法中，我相信您的NPE將會消失。