What to pass in Android Dialog fragment show() method's TAG parameter

Question

Hope you are doing well.

I created a dialog fragment and called show() on the instance. I passed a custom tag to show()'s parameter. The fragment requires no other arguments. On config change, resizing the window of the app, the app crashes.

     Caused by: android.view.InflateException: Binary XML file line #35 in com.signal.android.stage:layout/activity_main2: Binary XML file line #35 in com.signal.android.stage:layout/activity_main2: Error inflating class fragment
     Caused by: android.view.InflateException: Binary XML file line #35 in com.signal.android.stage:layout/activity_main2: Error inflating class fragment
     Caused by: java.lang.IllegalStateException: DialogFragment 0 doesn't exist in the FragmentManager
        at androidx.navigation.fragment.DialogFragmentNavigator.onRestoreState(DialogFragmentNavigator.java:148)

This is a method from the DialogFragmentNavigator.java:

    @Override
    public void onRestoreState(@Nullable Bundle savedState) {
        if (savedState != null) {
            mDialogCount = savedState.getInt(KEY_DIALOG_COUNT, 0);
            for (int index = 0; index < mDialogCount; index++) {
                DialogFragment fragment = (DialogFragment) mFragmentManager
                        .findFragmentByTag(DIALOG_TAG + index);
                if (fragment != null) {
                    fragment.getLifecycle().addObserver(mObserver);
                } else {
                    throw new IllegalStateException("DialogFragment " + index
                            + " doesn't exist in the FragmentManager");
                }
            }
        }
    }

Please see that the DIALOG_TAG that has been used has been hard coded to "androidx-nav-fragment:navigator:dialog:". So It makes sense that the Fragment is not found since I gave a custom TAG.

What is the expectation form the clients calling the show() method? What tag should be passed to gracefully restore the fragment?

Stay safe!

Answer 1

The change I have made to the mTag field of my custom DialogFragment class triggered this same crash when I try to restore the app from background.

As you can see from the source code you have posted, the tag field is set and use by DialogFragmentNavigator when restoring state. It simply means that you can't use a custom tag.

public final class DialogFragmentNavigator extends Navigator<DialogFragmentNavigator.Destination> {
    ...
    private static final String DIALOG_TAG = "androidx-nav-fragment:navigator:dialog:";

So you should either hard-code the prefix: show(... "androidx-nav-fragment:navigator:dialog:0")

or show it with the lib: navigate(R.id.you_dialog_fragment_defined_in_nav_graph_xml)

or may even dismiss it as a workaround to avoid the restoring process:

  override fun onPause() {
    super.onPause()
    dismiss()
  }