空指針異常旋轉裝置（SherlockDialogFragment）

Question

我：

public class LocationSelectionFragment extends SherlockDialogFragment implements 
     LocationImageChangeListener, DeleteActionListener { 
// some code... 
// ... 
    public void onLocationImageRemove(int position) { 
     Log.message("Enter"); 
     Log.variable("position", String.valueOf(position)); 
     mPosition = position; 
     ConfirmDeleteFragment deleteFragment = ConfirmDeleteFragment.NewInstance(mAdapter.getItem(position).locationName, this); 
     deleteFragment.show(getFragmentManager(), Constants.DELETE_DIALOG); 
    } 

    private void deleteRecord() { 
     LocationRecord record = mAdapter.getItem(mPosition); 

     mDbAdapter.deleteLocation(record._id); 
     mAdapter.remove(record); 
     mAdapter.notifyDataSetChanged(); 
    } 

    @Override 
    public void onDeleteLocation() { 
     Log.message("Enter"); 
     dismiss(); 
      //deleteRecord(); 

    } 

我ConfirmDeleteFragment類：

爲空指針異常

/** 
* Implements delete confirmation dialog 
*/ 
public class ConfirmDeleteFragment extends SherlockDialogFragment { 
    /** 
    * Interface for delete action 
    */ 
    public interface DeleteActionListener{ 
     /** 
     * Listener for handling delete location 
     */ 
     public void onDeleteLocation(); 
    } 

    private static DeleteActionListener mCallback; 
    private String mLocationName; 

    static public ConfirmDeleteFragment NewInstance(String locationName, DeleteActionListener callback) { 
     ConfirmDeleteFragment deleteDialog = new ConfirmDeleteFragment(); 
     deleteDialog.mLocationName = locationName; 
     ConfirmDeleteFragment.mCallback = callback; 
     return deleteDialog; 
    } 

    public ConfirmDeleteFragment() { 
     super(); 
    } 


    @Override 
    public Dialog onCreateDialog(Bundle savedInstanceState) { 
     Log.message("Enter"); 

     if (savedInstanceState != null) { 
      mLocationName = savedInstanceState.getString(Constants.DELETE_LOCATION_NAME); 
     } 

     String message = String.format(Locale.US, getString(R.string.sunset_deleteConfirm_message), mLocationName); 
     AlertDialog.Builder alertDialog = new AlertDialog.Builder(getActivity()); 

     // Setting Dialog Title 
     alertDialog.setTitle(R.string.sunset_deleteConfirm_title); 

     // Setting Dialog Message 
     alertDialog.setMessage(message); 

     // On pressing Delete button 
     alertDialog.setPositiveButton(R.string.sunset_deleteConfirm_positive, 
       new DialogInterface.OnClickListener() { 
        @Override 
        public void onClick(DialogInterface dialog, int which) { 
         dialog.dismiss(); 
         mCallback.onDeleteLocation(); 
        } 
       }); 

     // on pressing cancel button 
     alertDialog.setNegativeButton(R.string.sunset_deleteConfirm_negative, 
       new DialogInterface.OnClickListener() { 
        @Override 
        public void onClick(DialogInterface dialog, int which) { 
         dialog.cancel(); 
        } 
       }); 

     // Showing Alert Message 
     return alertDialog.create(); 
    } 

    @Override 
    public void onSaveInstanceState(Bundle outState) { 
     outState.putString(Constants.DELETE_LOCATION_NAME, mLocationName); 
    } 
} 

步驟：

1. 用戶打開的對話框LocationSelectionFragment。
2. 用戶單擊刪除圖像並打開ConfirmDeleteFragment。

3. 用戶旋轉設備並確認操作。結果 - 空指針異常：

   10-26 10:42:48.747: E/AndroidRuntime(3657): java.lang.NullPointerException 
   10-26 10:42:48.747: E/AndroidRuntime(3657):  at android.support.v4.app.DialogFragment.dismissInternal(DialogFragment.java:184) 
   10-26 10:42:48.747: E/AndroidRuntime(3657):  at android.support.v4.app.DialogFragment.dismiss(DialogFragment.java:155) 
   10-26 10:42:48.747: E/AndroidRuntime(3657):  at ru.neverdark.phototools.fragments.LocationSelectionFragment.onDeleteLocation(LocationSelectionFragment.java:231) 
   10-26 10:42:48.747: E/AndroidRuntime(3657):  at ru.neverdark.phototools.fragments.ConfirmDeleteFragment$1.onClick(ConfirmDeleteFragment.java:83) 
   10-26 10:42:48.747: E/AndroidRuntime(3657):  at com.android.internal.app.AlertController$ButtonHandler.handleMessage(AlertController.java:166) 
   10-26 10:42:48.747: E/AndroidRuntime(3657):  at android.os.Handler.dispatchMessage(Handler.java:99) 
   10-26 10:42:48.747: E/AndroidRuntime(3657):  at android.os.Looper.loop(Looper.java:137) 
   10-26 10:42:48.747: E/AndroidRuntime(3657):  at android.app.ActivityThread.main(ActivityThread.java:5103) 
   10-26 10:42:48.747: E/AndroidRuntime(3657):  at java.lang.reflect.Method.invokeNative(Native Method) 
   10-26 10:42:48.747: E/AndroidRuntime(3657):  at java.lang.reflect.Method.invoke(Method.java:525) 
   10-26 10:42:48.747: E/AndroidRuntime(3657):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737) 
   10-26 10:42:48.747: E/AndroidRuntime(3657):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 
   10-26 10:42:48.747: E/AndroidRuntime(3657):  at dalvik.system.NativeStart.main(Native Method) 
   

如果沒有旋轉裝置 - 做工精細。 在日誌中我可以看到什麼時候onResume方法在兩種情況下都調用了LocationSelectionFragment（帶有旋轉和無旋轉），但是在旋轉的情況下 - 當我調用Dismiss爲LocationSelectionFragment時使用。爲什麼？

Answer 1

我固定的空指針異常問題：

爲LocationSelectionFragment類重寫方法：

public void onLocationImageRemove(int position) { 
    Log.message("Enter"); 
    Log.variable("position", String.valueOf(position)); 

    ConfirmDeleteFragment deleteFragment = ConfirmDeleteFragment.NewInstance(mAdapter.getItem(position).locationName, position); 
    deleteFragment.setTargetFragment(this, Constants.DELETE_DIALOG_FRAGMENT); 
    deleteFragment.show(getFragmentManager(), Constants.DELETE_DIALOG); 
} 


public void onDeleteLocation(final int position) { 
    Log.message("Enter"); 

    Log.variable("Position", String.valueOf(position)); 

    dismiss(); 

} 

重寫類ConfirmDeleteFragment：

public class ConfirmDeleteFragment extends SherlockDialogFragment { 


    private String mLocationName; 
    private int mPosition; 

    static public ConfirmDeleteFragment NewInstance(String locationName, int position) { 
     ConfirmDeleteFragment deleteDialog = new ConfirmDeleteFragment(); 
     deleteDialog.mLocationName = locationName; 
     deleteDialog.mPosition = position; 
     return deleteDialog; 
    } 

    public ConfirmDeleteFragment() { 
     super(); 
    } 


    @Override 
    public Dialog onCreateDialog(Bundle savedInstanceState) { 
     Log.message("Enter"); 

     if (savedInstanceState != null) { 
      mLocationName = savedInstanceState.getString(Constants.DELETE_LOCATION_NAME); 
      mPosition = savedInstanceState.getInt(Constants.DELETE_LOCATION_POSITION); 
     } 

     String message = String.format(Locale.US, getString(R.string.sunset_deleteConfirm_message), mLocationName); 
     AlertDialog.Builder alertDialog = new AlertDialog.Builder(getActivity()); 

     // Setting Dialog Title 
     alertDialog.setTitle(R.string.sunset_deleteConfirm_title); 

     // Setting Dialog Message 
     alertDialog.setMessage(message); 

     // On pressing Delete button 
     alertDialog.setPositiveButton(R.string.sunset_deleteConfirm_positive, 
       new DialogInterface.OnClickListener() { 
        @Override 
        public void onClick(DialogInterface dialog, int which) { 
         dialog.dismiss(); 
((      LocationSelectionFragment) getTargetFragment()).onDeleteLocation(mPosition); 
        } 
       }); 

     // on pressing cancel button 
     alertDialog.setNegativeButton(R.string.sunset_deleteConfirm_negative, 
       new DialogInterface.OnClickListener() { 
        @Override 
        public void onClick(DialogInterface dialog, int which) { 
         dialog.cancel(); 
        } 
       }); 

     // Showing Alert Message 
     return alertDialog.create(); 
    } 

    @Override 
    public void onSaveInstanceState(Bundle outState) { 
     outState.putString(Constants.DELETE_LOCATION_NAME, mLocationName); 
     outState.putInt(Constants.DELETE_LOCATION_POSITION, mPosition); 
    } 

它解決了我的問題。