如何保存我的片段中的接口狀態？

Question

我有一個Activity，它使用ViewPager在ViewPager類中創建三個Fragment s，當它們被創建時，我將Fragment s設置爲setRetainInstace(true);。

在我的Fragment s之內，我顯示了一些可編輯的信息。此Fragment啓動DialogFragment來編輯信息。

當用戶未更改方向時，我可以更新信息並將結果發送回視圖中的片段，但是，一旦我更改了方向並更新了信息，我的Interface已附加在DialogFragment s onAttach()方法我得到NullPointerException。

我不明白爲什麼，因爲每次啓動新的DialogFragment時總會調用onAttach()方法。

我應該如何解決這個問題？ 我可以保存界面的狀態嗎？如果是的話如何？

這是我DialogFragment代碼： 的GenericDialogFragment類僅用於更改外觀

public class Fragment1 extends GenericDialogFragment implements WebServiceResult{ 



// ------------------------------------------------------------------------- 
// Member Variables 
//-------------------------------------------------------------------------- 
//Webservice Callback 
private WSRequest mActiveRequest = null; 
// The Current Context of the Application 
private Context mClassContext = null; 
// Interface reference for communication 
private static CommunicateResults communicateResults = null; 


// ------------------------------------------------------------------------- 
// New Instance Method 
//--------------------------------------------------------------------------  

public static Fragment1 newInstance(int userId, GenericObject [] objects, GenericGroup [] groups, Object currentObject){ 
    // Initialize a new Fragment1 
    Fragment1 fragment = new Fragment1(); 
    // Create a new Bundle 
    Bundle args = new Bundle(); 

    fragment.setArguments(args); 

    // Return the Fragment1 
    return fragment; 
} 

// ------------------------------------------------------------------------- 
// Class Functions/Methods 
//--------------------------------------------------------------------------  

// States that the Interface is attached to the parent activity 
@Override public void onAttach(Activity activity) 
{ 
    // Perform the Default Behavior 
    super.onAttach(activity); 
    Log.d("ONAttach()","On attach() is called"); 
    // Try 
    try{ 
     // Attach the interface to the activity 
     communicateResults = (CommunicateResults) ((MainActivity) getActivity()).findFragment(EditableFragment1.class); 

    }catch(Exception ex){ 
     // Print the stack trace 
     ex.printStackTrace(); 
    } 
} 

// States that the Dialog's View has been Created 
@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){ 
    // Return the Inflated XML Layout 
    return inflater.inflate(R.layout.fragment1, container, false); 
} 

// States that the fragment has been created, last chance to update the UI 
@Override 
public void onActivityCreated(Bundle savedInstanceState){ 
    // Perform the Default behavior 
    super.onActivityCreated(savedInstanceState); 

    mClassContext = getActivity(); 

    // Get the Arguments passed into the Fragment instance 
    savedStateData = getArguments(); 

    // Reference all the UI Elements in the View  


    // Add listeners to the Button Widgets 


    // If the savedInstanceState is not null, get the current object 
    if(savedStateData != null){ 

     // Get the object out of the state data 
     mCurrentObject = savedStateData.getParcelable(STATE_DATA_CURRENT_OBJECT); 

    } 



} 


//----------------------------------------------------------------------------- 
// Webservice Callback methods 
//----------------------------------------------------------------------------- 

// States that the web service has succeeded 
@Override public void webserviceSucceeded(WebServiceBase finishedService, Object responseData) 
{ 

    Log.d("EDIT Object", responseData.toString()); 

    if(responseData != null){ 

     if(mDeletingObject){ 



      // Send Back to the object to remove 
      communicateResults.sendBackData(mCurrentObject, ACTION_DELETE); 

     }else{ 

      JSONObject tempObject = (JSONObject) responseData; 

      try{ 

       // Parse Data ... 



      }catch(Exception ex){ 

       ex.printStackTrace(); 
       // TODO: The Object was deleted from the Lest 
      } 

      // If we are creating a object, bundle the information to pass to the parent activity 
      if(mCreatingObject){ 

       // Create a new Workout Object 
       mCurrentObject = new Object(); 


       // Callback to Parent Activity to notify that data has changed 
       communicateResults.sendBackData(mCurrentObject, ACTION_CREATE); 

       // Else the Object was updated 
      }else{ 
       // Create a new Object 
       mCurrentObject = new Object(); 


       // Callback to Parent Activity to notify that data has changed 
       communicateResults.sendBackData(mCurrentObject, ACTION_UPDATE); 
      } 
     } 


    } 

    // Dismiss the fragment 


} 


// States that the web service has failed 
@Override 
public void webserviceFailed(WebServiceBase finishedService, 
     Object errorData) { 


    // Display the Error 
    displayErrorData(errorData); 

} 

}

Answer 1

我認爲你正在尋找onActivityCreated(Bundle bundle);，這是Fragment相當於Activity班的onRestoreSavedInstanceState(Bundle bundle);。

從文檔：

公共無效onActivityCreated（捆綁savedInstanceState）添加在 API級別11

片段的活動已創建時調用，這 片段的視圖層次實例化。一旦這些部分到位，它就可以用來執行最終的初始化 ，例如檢索 視圖或恢復狀態。對於使用setRetainInstance（boolean）來保留其實例的片段也很有用，因爲此回調告知片段何時與新活動 實例完全關聯。這是在onCreateView（LayoutInflater，ViewGroup， Bundle）之前和onViewStateRestored（Bundle）之前調用的。參數 savedInstanceState如果正在從 先前保存的狀態重新創建片段，則爲狀態。

當您的片段上的取向變化破壞，保存其作爲活動的Bundle名稱值對的狀態，那麼當需要重新創建它，實例化在這種方法的新Interface，並設置相應字段/檢索新的Fragment實例中的可分發內容。