无法恢复活动(包含一个SupportMapFragment)，恢复时在R.id.map处发生NPE

Question

我有一个片段，其中包含在onResume中定义的地图视图，如下面的代码所示。当我退出片段并返回或在不同的片段中移动并返回到这个地图片段时，我不会遇到任何错误或问题。然而，当我从下面提供的按钮转到谷歌地图应用程序并回到这个片段时，它在findFragmentById(R.id.map)和logcat上给出NPE，说"无法恢复活动"。

编辑:每当onCreateView被调用，它的工作，但当onResume或onStart被调用它崩溃。我之前说错了。编辑。公共类Fragment2扩展Fragment {

    ...
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        View rootView = inflater.inflate(R.layout.fragment_fragment2,
                container, false);

        return rootView;
    }
    @Override
    public void onResume() {
        // TODO Auto-generated method stub
        super.onResume();
        map = ((SupportMapFragment) getFragmentManager().findFragmentById
**NPE here**      (R.id.map)).getMap();
              ...
            }
    public void onPause() {
        // TODO Auto-generated method stub
        super.onPause();
        SupportMapFragment f = (SupportMapFragment) getFragmentManager()
                .findFragmentById(R.id.map);
        if (f != null)
            getFragmentManager().beginTransaction().remove(f).commit();
    }

下面是logcat:-

06-07 21:32:43.295: E/AndroidRuntime(27112): FATAL EXCEPTION: main
06-07 21:32:43.295: E/AndroidRuntime(27112): java.lang.RuntimeException: Unable to resume activity {com.example.mapsapiv2demo/com.example.mapsapiv2demo.MainActivity}: java.lang.NullPointerException
06-07 21:32:43.295: E/AndroidRuntime(27112):    at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2869)
06-07 21:32:43.295: E/AndroidRuntime(27112):    at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2898)
06-07 21:32:43.295: E/AndroidRuntime(27112):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1289)
06-07 21:32:43.295: E/AndroidRuntime(27112):    at android.os.Handler.dispatchMessage(Handler.java:99)
06-07 21:32:43.295: E/AndroidRuntime(27112):    at android.os.Looper.loop(Looper.java:137)
06-07 21:32:43.295: E/AndroidRuntime(27112):    at android.app.ActivityThread.main(ActivityThread.java:5226)
06-07 21:32:43.295: E/AndroidRuntime(27112):    at java.lang.reflect.Method.invokeNative(Native Method)
06-07 21:32:43.295: E/AndroidRuntime(27112):    at java.lang.reflect.Method.invoke(Method.java:511)
06-07 21:32:43.295: E/AndroidRuntime(27112):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:795)
06-07 21:32:43.295: E/AndroidRuntime(27112):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:562)
06-07 21:32:43.295: E/AndroidRuntime(27112):    at dalvik.system.NativeStart.main(Native Method)
06-07 21:32:43.295: E/AndroidRuntime(27112): Caused by: java.lang.NullPointerException
06-07 21:32:43.295: E/AndroidRuntime(27112):    at com.example.mapsapiv2demo.Fragment2.onResume(Fragment2.java:56)
06-07 21:32:43.295: E/AndroidRuntime(27112):    at android.support.v4.app.Fragment.performResume(Fragment.java:1503)
06-07 21:32:43.295: E/AndroidRuntime(27112):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:947)
06-07 21:32:43.295: E/AndroidRuntime(27112):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1088)
06-07 21:32:43.295: E/AndroidRuntime(27112):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1070)
06-07 21:32:43.295: E/AndroidRuntime(27112):    at android.support.v4.app.FragmentManagerImpl.dispatchResume(FragmentManager.java:1871)
06-07 21:32:43.295: E/AndroidRuntime(27112):    at android.support.v4.app.FragmentActivity.onResumeFragments(FragmentActivity.java:455)
06-07 21:32:43.295: E/AndroidRuntime(27112):    at android.support.v4.app.FragmentActivity.onPostResume(FragmentActivity.java:444)
06-07 21:32:43.295: E/AndroidRuntime(27112):    at android.app.Activity.performResume(Activity.java:5195)
06-07 21:32:43.295: E/AndroidRuntime(27112):    at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2859)

Answer 1

您正在删除onPause中的子片段，当onResume稍后被调用时，它不存在，因此NPE的原因。

另一件事是，你不应该把子片段在xml。始终从代码中添加它们。

还有一件事是你应该使用getChildFragmentManager而不是getFragmentManager时，添加片段到片段。

请看这里的代码:http://code.google.com/p/gmaps-api-issues/issues/detail?id=5064#c1作为一个例子。

编辑:

注意:当布局包含<fragment>时，您不能将布局膨胀为片段。嵌套片段只有在动态添加到片段时才被支持。

: http://developer.android.com/about/versions/android-4.2.html NestedFragments