Android：为什么DialogFragment在方向改变时返回nullpointer

Question

我有一个问题，正确的对话片段删除后，方向被改变。我想这是由于旧的上下文，因为在该活动被重新创建后，会创建一个新的活动和相应的上下文。我知道我可以在onSaveInstance中设置一些变量来保存对话框状态，如果必要的话重新创建对话框，或者只在清单“定向”中放置一个属性。但是，也许有更好的方法来做到这一点，不在manifest中硬编码，也不在onSaveIntance中手动保存？我还尝试在main片段和dialog片段中使用SetRetaInstane，但这对我没有帮助。

片段：

public class MainFragment extends Fragment implements ServiceExecutorListener, OnClickListener, DialogClickListener {

private static final String TAG = MainFragment.class.getName();

private TextView serviceStatus;
Intent intent;
Boolean bound = false;
ServiceConnection sConn;
RESTService service;
ProgressDialogFragment pd;
private Button btnSend, btnCheck;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    Log.d(TAG, "onCreate");
    setRetainInstance(true);
    intent = new Intent(getActivity(), RESTService.class);
    getActivity().startService(intent);
    sConn = new ServiceConnection() {

        @Override
        public void onServiceConnected(ComponentName name, IBinder binder) {
            Log.d(TAG, "MainFragment onServiceConnected");
            service = ((RESTService.MyBinder) binder).getService();
            service.registerListener(MainFragment.this);
            if (service.tasksAreDone())
                serviceStatus.setText(service.getResult());
            bound = true;
        }

        public void onServiceDisconnected(ComponentName name) {
            Log.d(TAG, "MainFragment onServiceDisconnected");
            bound = false;
        }

    };
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.main_fragment, container, false);
    serviceStatus = (TextView) rootView.findViewById(R.id.tvServiceStatusValue);
    btnSend = (Button) rootView.findViewById(R.id.btnSend);
    btnCheck = (Button) rootView.findViewById(R.id.btnCheck);

    btnSend.setOnClickListener(this);
    btnCheck.setOnClickListener(this);
    return rootView;
}

@Override
public void onClick(View v) {
    switch (v.getId()) {
        case R.id.btnSend:
            pd = new ProgressDialogFragment();
            pd.newInstance(null);
            pd.setDialogClickListener(this);
            pd.show(getActivity().getSupportFragmentManager(), "ProgressDialog");
            service.run(RESTService.REQUEST, 7);
            service.run(RESTService.REQUEST, 2);
            service.run(RESTService.REQUEST, 4);
            break;
        case R.id.btnCheck:
            if (service != null)
                serviceStatus.setText(String.valueOf(service.tasksAreDone()) + service.getTasksCount());
            break;
    }
}

@Override
public void onStart() {
    super.onStart();
    Log.d(TAG, "onStart: Bind service");
    getActivity().bindService(intent, sConn, 0);
}

@Override
public void onPause() {
    super.onPause();
    Log.d(TAG, "onPause: Unbind service");
    if (!bound)
        return;
    getActivity().unbindService(sConn);
    service.unregisterListener();
    bound = false;
}

@Override
public void onComplete(int taskID, int action, String result) {
    Log.d(TAG, "Task #" + taskID + ", action = " + action + " Completed");
    pd.dismiss();
    serviceStatus.setText(result);
}

@Override
public void onDialogClick(int action) {
    switch (action) {
        case Dialog.BUTTON_POSITIVE:
            Log.d(TAG, "POSITIVE BUTTON");
            break;
        case Dialog.BUTTON_NEGATIVE:
            Log.d(TAG, "NEGATIVE BUTTON");
            service.removeTasks();
            break;
        case Dialog.BUTTON_NEUTRAL:
            Log.d(TAG, "NEUTRAL BUTTON");
            break;
    }
}

@Override
public void onDestroy() {
    super.onDestroy();
    Log.d(TAG, "onDestroy");
}
}

public class ProgressDialogFragment extends DialogFragment implements OnClickListener {

final String TAG = ProgressDialogFragment.class.getName();
private DialogClickListener listener;

public ProgressDialogFragment newInstance(Bundle args) {
    ProgressDialogFragment pdf = new ProgressDialogFragment();
    pdf.setArguments(args);
    return pdf;
}

public void setDialogClickListener(DialogClickListener listener) {
    this.listener = listener;
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setRetainInstance(true);
    Log.d(TAG, "onCreate");
}

public Dialog onCreateDialog(Bundle savedInstanceState) {
    AlertDialog.Builder adb = new AlertDialog.Builder(getActivity())
            .setTitle("Title!")
            .setPositiveButton(R.string.yes, this)
            .setNegativeButton(R.string.no, this)
            .setNeutralButton(R.string.maybe, this)
            .setCancelable(false)
            .setMessage(R.string.message_text)
            .setOnKeyListener(new OnKeyListener() {
                @Override
                public boolean onKey(DialogInterface dialog, int keyCode, KeyEvent event) {
                    return true;
                }
            });
    return adb.create();
}

public void onClick(DialogInterface dialog, int which) {
    if (listener != null)
        listener.onDialogClick(which);
}

public void onDismiss(DialogInterface dialog) {
    Log.d(TAG, "Dialog: onDismiss, dialog = " + getDialog() + ", retainInstance = " + getRetainInstance());
    // Fix to avoid simple dialog dismiss in orientation change
    if ((getDialog() != null) && getRetainInstance())  
        getDialog().setDismissMessage(null);

}

public void onCancel(DialogInterface dialog) {
    super.onCancel(dialog);
    Log.d(TAG, "Dialog: onCancel");
}

04-29 06:17:17.860: E/AndroidRuntime(4202): FATAL EXCEPTION: main
04-29 06:17:17.860: E/AndroidRuntime(4202): java.lang.NullPointerException
04-29 06:17:17.860: E/AndroidRuntime(4202):     at android.support.v4.app.DialogFragment.dismissInternal(DialogFragment.java:184)
04-29 06:17:17.860: E/AndroidRuntime(4202):     at android.support.v4.app.DialogFragment.dismiss(DialogFragment.java:155)
04-29 06:17:17.860: E/AndroidRuntime(4202):     at com.example.restservice.fragments.MainFragment.onComplete(MainFragment.java:108)
04-29 06:17:17.860: E/AndroidRuntime(4202):     at com.example.restservice.service.RESTService$1.run(RESTService.java:79)
04-29 06:17:17.860: E/AndroidRuntime(4202):     at android.os.Handler.handleCallback(Handler.java:605)
04-29 06:17:17.860: E/AndroidRuntime(4202):     at android.os.Handler.dispatchMessage(Handler.java:92)
04-29 06:17:17.860: E/AndroidRuntime(4202):     at android.os.Looper.loop(Looper.java:137)
04-29 06:17:17.860: E/AndroidRuntime(4202):     at android.app.ActivityThread.main(ActivityThread.java:4514)
04-29 06:17:17.860: E/AndroidRuntime(4202):     at java.lang.reflect.Method.invokeNative(Native Method)
04-29 06:17:17.860: E/AndroidRuntime(4202):     at java.lang.reflect.Method.invoke(Method.java:511)
04-29 06:17:17.860: E/AndroidRuntime(4202):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:790)
04-29 06:17:17.860: E/AndroidRuntime(4202):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:557)
04-29 06:17:17.860: E/AndroidRuntime(4202):     at dalvik.system.NativeStart.main(Native Method)

编辑：

如果我把setRetaInstance（true）放在main fragment中，它调用dialogFragment，而把dialogFragment放在onCreate方法中，那么我会看到getRetaInstance返回true，并且getDialog在方向改变的过程中有对象（否则是NPE）。在这种情况下，我也没有NPE，但会有以下奇怪的行为：对话框创建和呈现，对话框重新创建（方向改变）和取消（为什么？），对话框重新创建（方向再次改变）和呈现（wtf？上次它被取消了）等等，即对话框在一边被取消，但记住在另一边它应该被提出。那是什么？

Answer 1

从oncreateDialog（Bundle savedInstanceState）中移除setrateInstance（true）；并将其保留在onCreate（Bundle savedInstance）中，如下所示：

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setRetainInstance(true);
}