Question

我正在用两个片段写一个应用程序。 First片段将文本信息发送到创建两个片段的活动。这工作完美。我的第二个片段与第一个片段同时创建。第二个片段在其xml布局中包含textview。我的主要活动应该将基于文本的数据传递给第二个片段，并且应该显示文本。问题是当文本到达第二个片段方法时，textview alwasy返回一个空指针。

//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);
    }
}

堆栈追踪：

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

您为什么要重新设置displayedMessage var？你在onCreateView中设置它并将它作为一个类变量，所以当你调用serMessage方法时它应该仍然存在。

只需将findViewById放入setMesage方法即可，我相信您的NPE会消失。

Answer 2

我发现了我的错误。我尝试在第一个片段回调期间调用第二个片段，因为片段无法直接通信而抛出NPE。

在Fragment中更新Textview时为空指针

2 个答案: