DialogFragment callback on orientation change

问题:

I'm migrating my dialogs, currently using Activity.showDialog(DIALOG_ID);, to use the DialogFragment system as discussed in the android reference.

There's a question that arose during my development when using callbacks to deliver some event back to the activity/fragment that opened the dialog:

Here's some example code of a simple dialog:

public class DialogTest extends DialogFragment {

public interface DialogTestListener {
    public void onDialogPositiveClick(DialogFragment dialog);
}

// Use this instance of the interface to deliver action events
static DialogTestListener mListener;

public static DialogTest newInstance(Activity activity, int titleId, int messageId) {
    udateListener(activity);
    DialogTest frag = new DialogTest();
    Bundle args = new Bundle();
    args.putInt("titleId", titleId);
    args.putInt("messageId", messageId);
    frag.setArguments(args);
    return frag;
}

public static void udateListener(Activity activity) {
    try {
        // Instantiate the NoticeDialogListener so we can send events with it
        mListener = (DialogTestListener) activity;
    } catch (ClassCastException e) {
        // The activity doesn't implement the interface, throw exception
        throw new ClassCastException(activity.toString() + " must implement DialogTestListener");
    }
}


@Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
    int titleId = getArguments().getInt("titleId");
    int messageId = getArguments().getInt("messageId");

    AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
    // dialog title
    builder.setTitle(titleId);
    // dialog message
    builder.setMessage(messageId);

    // dialog negative button
    builder.setNegativeButton("No", new OnClickListener() {
               public void onClick(DialogInterface dialog, int id) {}});
    // dialog positive button
    builder.setPositiveButton("Yes", new OnClickListener() {
        public void onClick(DialogInterface dialog, int id) {
            mListener.onDialogPositiveClick(DialogTest.this);
        }});

    // create the Dialog object and return it
    return builder.create();
}}

And here's some activity code calling it:

public class SomeActivity extends FragmentActivity implements DialogTestListener {
private EditText mUserName;
@Override
public void onCreate(Bundle savedInstanceState) {
    // setup ui
    super.onCreate(savedInstanceState);
    setContentView(R.layout.ui_user_edit);
    // name input
    mUserName = (EditText) findViewById(R.id.userEdit_editTextName);
}

@Override
public void onDialogPositiveClick(DialogFragment dialog) {
    Log.d(TAG, this.toString());
    mUserName.setText(mUserName.getText() + "1");
}

private void showDialog() {
    DialogTest test = DialogTest.newInstance(SomeActivity.this, R.string.someTitleText, R.string.someMessageText);
    test.show(getSupportFragmentManager(), "testDialog");
}}

The code is pretty much what you see the reference. Problem is, that once you do a orientation change, when a dialog is shown, it stops working as expected --> Due to the activity lifecycle, both, the activity and the dialog are rebuild, and the dialog now does not have the proper reference to the new rebuilt activity.

I added the following code to my activitys onResume method:

    @Override
protected void onResume() {
    super.onResume();
    DialogTest.udateListener(this);
}

Doing this, I get the expected behavior, and the dialog sends events back to the new rebuilt activity when an orientation change occured.

My question is: What is the 'best practice' to handle the callbacks between the DialogFragment which was opened by a FragmentActivity during an orientation change?

Best regards

回答1:

Yeah, this is a common trap I'm falling in all the time myself. First of all let me say that your solution of calling DialogTest.udateListener() in onResume() seems to be fully appropriate to me.

An alternative way would be to use a ResultReceiver which can be serialized as a Parcelable:

public class DialogTest extends DialogFragment {

public static DialogTest newInstance(ResultReceiver receiver, int titleId, int messageId) {
    DialogTest frag = new DialogTest();
    Bundle args = new Bundle();
    args.putParcelable("receiver", receiver);
    args.putInt("titleId", titleId);
    args.putInt("messageId", messageId);
    frag.setArguments(args);
    return frag;
}

@Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
    int titleId = getArguments().getInt("titleId");
    int messageId = getArguments().getInt("messageId");
    ResultReceiver receiver = getArguments().getParcelable("receiver");

    AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
    // dialog title
    builder.setTitle(titleId);
    // dialog message
    builder.setMessage(messageId);

    // dialog negative button
    builder.setNegativeButton("No", new OnClickListener() {
        public void onClick(DialogInterface dialog, int id) {
            receiver.sendResult(Activity.RESULT_CANCEL, null);
        }});
    // dialog positive button
    builder.setPositiveButton("Yes", new OnClickListener() {
        public void onClick(DialogInterface dialog, int id) {
            receiver.sendResult(Activity.RESULT_OK, null);
        }});

    // create the Dialog object and return it
    return builder.create();
}}

Then you can handle everything in the Receiver like this:

protected void onReceiveResult(int resultCode, Bundle resultData) {
    if (getActivity() != null){
        // Handle result
    }
}

Check out ResultReceiver doesn't survire to screen rotation for more details. So in the end you probably still need to rewire the ResultReceiver with your Activity. The only difference is that you decouple the Activity from the DialogFragment.

回答2:

There is better solution instead of using static methods and variables because it would work only fro one instance of your dialog. It is better to store your callback as non static member

private DialogTestListener mListener;
public void setListener (DialogTestListener listener){
  mListener = listener;
}

Then you should show your dialog using TAG like this mDialogFragment.show(getSupportFragmentManager(), DIALOG_TAG);

And then in onResume method of your activity you can reset your listener

protected void onResume() {
   super.onResume();
   mDialogFragment = (CMFilterDialogFrg) getSupportFragmentManager().findFragmentByTag(DIALOG_TAG);
   if(mDialogFragment  != null){
       mDialogFragment.setListener(yourListener)
   }
}

回答3:

While André's solution works, a better solution is to get the updated activity during onAttach() in your Fragment.

private DialogTestListener mListener;

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

With this solution, you won't need to pass the Activity in newInstance() anymore. You just need to make sure the Activity owning your Fragment is a DialogTestListener. You also don't need to save the state like in the ResultReceiver solution.

回答4:

First, call setTargetFragment from FragmentParent to start dialogFragment. In dialogFragment use getTargetFragment to callback fragment and return data. All data result will excute in onactivityresult of FragmentParent

follow this link: Receive result from DialogFragment

回答5:

Another way is that you can stop the activity getting recreated. You have to tell Android that you'll handle the orientation change yourself and android won't recreate your activity. You need to add this for your activity to your manifest file:

android:configChanges="keyboardHidden|orientation"

If not this, then you can use standard onSaveInstanceState() to save your state and recover using savedInstanceState as recommended by Google.

Here's Google's official guide for it: http://developer.android.com/guide/components/activities.html#Lifecycle

Go through it if you haven't already. It'll really help you in android development.