getActivity == null，試圖onattach

Question

我嘗試啓動我的應用程序，我可以看到我的片段正在加載，但每當我的適配器嘗試將數據放入我的listview時，我的應用程序崩潰。這是因爲我的getActivity（）= null。現在我試圖查看它，我發現你必須打開它？但我試過了，或者我做錯了..它不起作用任何人都可以幫助我愉快嗎？

以下是錯誤：

11-24 13:00:27.429: E/AndroidRuntime(31304): FATAL EXCEPTION: main 
11-24 13:00:27.429: E/AndroidRuntime(31304): java.lang.NullPointerException 
11-24 13:00:27.429: E/AndroidRuntime(31304): at android.widget.ArrayAdapter.init(ArrayAdapter.java:310) 
11-24 13:00:27.429: E/AndroidRuntime(31304): at android.widget.ArrayAdapter.<init>(ArrayAdapter.java:153) 
11-24 13:00:27.429: E/AndroidRuntime(31304): at com.laurenswuyts.witpa.ListEventAdapter.<init>(ListEventAdapter.java:23) 
11-24 13:00:27.429: E/AndroidRuntime(31304): at com.laurenswuyts.witpa.EventFragment.parseEventFromFQLResponse(EventFragment.java:154) 
11-24 13:00:27.429: E/AndroidRuntime(31304): at com.laurenswuyts.witpa.EventFragment$2.onCompleted(EventFragment.java:119) 
11-24 13:00:27.429: E/AndroidRuntime(31304): at com.facebook.Request$4.run(Request.java:1669) 
11-24 13:00:27.429: E/AndroidRuntime(31304): at android.os.Handler.handleCallback(Handler.java:615) 
11-24 13:00:27.429: E/AndroidRuntime(31304): at android.os.Handler.dispatchMessage(Handler.java:92) 
11-24 13:00:27.429: E/AndroidRuntime(31304): at android.os.Looper.loop(Looper.java:137) 
11-24 13:00:27.429: E/AndroidRuntime(31304): at android.app.ActivityThread.main(ActivityThread.java:4944) 
11-24 13:00:27.429: E/AndroidRuntime(31304): at java.lang.reflect.Method.invokeNative(Native Method) 
11-24 13:00:27.429: E/AndroidRuntime(31304): at java.lang.reflect.Method.invoke(Method.java:511) 
11-24 13:00:27.429: E/AndroidRuntime(31304): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1038) 
11-24 13:00:27.429: E/AndroidRuntime(31304): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:805) 
11-24 13:00:27.429: E/AndroidRuntime(31304): at dalvik.system.NativeStart.main(Native Method) 

這裏是我的mainactivity：

public class EventFragment extends Fragment { 

     //Arraylist with event details 
     private static List<EventDetails> dataEvent; 

     //Adapter to put event details in listview 
     ListEventAdapter eventAdapter; 

     //Listview with the events 
     ListView lvEvents; 

     //To show Progress Circle 
     LinearLayout linearProgress; 

     private static final String TAG = "EventFragment"; 

     private static final int REAUTH_ACTIVITY_CODE = 100; 

    @Override 
    public void onAttach(Activity activity) { 
     super.onAttach(activity); 
    } 

     @Override 
     public View onCreateView(LayoutInflater inflater, 
       ViewGroup container, Bundle savedInstanceState) { 
      super.onCreateView(inflater, container, savedInstanceState); 
      View view = inflater.inflate(R.layout.event, 
        container, false); 
      linearProgress = (LinearLayout) view.findViewById(R.id.linProgress); 
      lvEvents = (ListView) view.findViewById(R.id.lvEvent); 
      // Check for an open session 
      Session session = Session.getActiveSession(); 
      if (session != null && session.isOpened()) { 
       // Get the user's data 
       ShowEventsFromFQL(); 

      } 
      return view; 
     } 

     @Override 
     public void onCreate(Bundle savedInstanceState) { 
      super.onCreate(savedInstanceState); 
      uiHelper = new UiLifecycleHelper(getActivity(), callback); 
      uiHelper.onCreate(savedInstanceState); 


     } 


     public void ShowEventsFromFQL(){ 
      // Check for an open session 
      Session session = Session.getActiveSession(); 
      if (session != null && session.isOpened()) { 

       //Progressbar active   
       linearProgress.setVisibility(View.VISIBLE); 


       // Get the user's data 
       // ORDER BY attending_count DESC 
       String fqlQuery = "....."; 
       Bundle params = new Bundle(); 
       params.putString("q", fqlQuery); 
       Session session2 = Session.getActiveSession(); 
       Request request = new Request(session2, 
        "/fql",       
        params,       
        HttpMethod.GET,     
        new Request.Callback(){   
         public void onCompleted(Response response) { 
          Log.i(TAG, "Result: " + response.toString()); 
          parseEventFromFQLResponse(response);             
         }     
       }); 
       Request.executeBatchAsync(request); 
     }   
     } 

     public final void parseEventFromFQLResponse(Response response) 
     { 
      dataEvent = new ArrayList<EventDetails>(); 
      try 
      { 
       GraphObject graphObj = response.getGraphObject(); 
       JSONObject jsonObj = graphObj.getInnerJSONObject(); 
       JSONArray jsonArr = jsonObj.getJSONArray("data"); 

       for (int i = 0; i < (jsonArr.length()); i++) 
       { 
        JSONObject jObject = jsonArr.getJSONObject(i); 

         int attending_count = jObject.getInt("attending_count"); 
         String name = jObject.getString("name"); 
         String host = jObject.getString("host"); 
         String description = jObject.getString("description"); 
         String location = jObject.getString("location");   
         String start_time = jObject.getString("start_time"); 
         String end_time = jObject.getString("end_time"); 


         dataEvent.add(new EventDetails(attending_count, name, host, description, location, start_time, end_time)); 


       } 
      // if(dataEvent != null){ 
if(getActivity() == null){ 
       Log.i(TAG, "Result: loser"); 
      } 
      else { 
       Log.i(TAG, "Result: nope"); 
      } 

       eventAdapter = new ListEventAdapter(getActivity(), R.layout.event_item, dataEvent); 

       lvEvents.setAdapter(eventAdapter); 
       eventAdapter.notifyDataSetChanged(); 

       //Progressbar gone 
       linearProgress.setVisibility(View.GONE); 

      // } 
      } 
      catch (JSONException e) { 
       e.printStackTrace(); 
      } 
     } 


     @Override 
     public void onActivityResult(int requestCode, int resultCode, Intent data) { 
      super.onActivityResult(requestCode, resultCode, data); 
      if (requestCode == REAUTH_ACTIVITY_CODE) { 
       uiHelper.onActivityResult(requestCode, resultCode, data); 
      } 
     } 


     private void onSessionStateChange(final Session session, SessionState state, Exception exception) { 
      if (session != null && session.isOpened()) { 
       // Get the user's data. 
       ShowEventsFromFQL(); 

      } 
     } 

     private UiLifecycleHelper uiHelper; 
     private Session.StatusCallback callback = new Session.StatusCallback() { 
      @Override 
      public void call(final Session session, final SessionState state, final Exception exception) { 
       onSessionStateChange(session, state, exception); 
      } 
     }; 

     @Override 
     public void onResume() { 
      super.onResume(); 
      uiHelper.onResume(); 
     } 

     @Override 
     public void onSaveInstanceState(Bundle bundle) { 
      super.onSaveInstanceState(bundle); 
      uiHelper.onSaveInstanceState(bundle); 
     } 

     @Override 
     public void onPause() { 
      super.onPause(); 
      uiHelper.onPause(); 
     } 

     @Override 
     public void onDestroy() { 
      super.onDestroy(); 
      uiHelper.onDestroy(); 
     } 


    } 

在此先感謝！

Answer 1

您在片段的onCreateView（）方法中做了很多工作。一旦片段應該創建其用戶界面，Android會調用onCreateView（）方法。我會建議）移動這確實異步部分的onActiviyCreated（部分如：

@Override 
public void onActivityCreated(Bundle savedInstanceState) { 
    super.onActivityCreated(savedInstanceState); 


    // Check for an open session 
    Session session = Session.getActiveSession(); 
    if (session != null && session.isOpened()) { 
     // Get the user's data 
     ShowEventsFromFQL(); 
    } 
} 

Answer 2

我沒有實際周圍的源代碼挖出來證實這一點，但我的經驗，當你從膨脹片段XML或將其添加到活動的onCreate，getActivity()直到onCreateView()或onActivityCreated()纔有效。我通常不使用onAttached()來表示getActivity()有效。