getViewLifecycleOwner() in DialogFragment leads to crash

Question

I use DialogFragment (onCreateDialog) and ViewModel for it. But, when I try to pass getViewLifecycleOwner() to the LiveData::observe method I get the error below:

java.lang.IllegalStateException: Can't access the Fragment View's LifecycleOwner when getView() is null i.e., before onCreateView() or after onDestroyView().

Is it possible to use getViewLifecycleOwner() inside a DialogFragment?

Solution 1

This happens because of how the DialogFragment is created. If you use onCreateDialog() than a slightly different lifecycle is used for this type of Fragment. The onCreateView() will not be used, thus the viewLifecycleOwner for this Fragment won't be initialized.

As a workaround for this, you can use the Fragment instance as the owner for the observer: .observe(this, Observer {...}. Although you will get a warning for using this instead of the viewLifecycleOwner.

Solution 2

Your case is slightly different but I think the concept is kind of the same. Just use this.getActivity() in your Dialog Class and pass it as LifeCycleOwner. I had the same problem because I used LiveData and Retrofit and LiveData needs a reference. The DialogFragment sets its LifeCycleOwner at some point but it is not at any of the methods mentioned above. By using the getActivity() you can use your observer as early as in onCreateDialog method. Here is some portion of my code that at first caused some issue when I tried to pass a null referenced this.getViewLifecycleOwner() instead of the activity.

@NonNull
@Override
public Dialog onCreateDialog(@Nullable Bundle savedInstanceState) {
       FragmentActivity activity = this.getActivity();
       binding = DialogSelectIssuesBinding.inflate(LayoutInflater.from(getContext()));

       RetroRepository.
            getDefault().
            getAllIssues().
            observe(this.getActivity(), listLiveDataResponse -> {
                //ToDo Check for errors and Bind the data here 
            });


       AlertDialog alertDialog = new AlertDialog.Builder(activity)
                            .setView(binding.getRoot())
                            .setTitle("Please select issues from the list below:")
                            .setNegativeButton("CANCEL", null)
                            .setPositiveButton("ADD", null)
                            .create();
       alertDialog.setCanceledOnTouchOutside(false);
       return alertDialog;
}

Solution 3

This is the official recommendation for DialogFragments:

Note: When subscribing to lifecycle-aware components such as LiveData, you should never use viewLifecycleOwner as the LifecycleOwner in a DialogFragment that uses Dialogs. Instead, use the DialogFragment itself, or if you're using Jetpack Navigation, use the NavBackStackEntry.

So you can just observe things as normal, but instead of viewLifecycleOwner you pass this, or the current backstack entry (e.g. findNavController().currentBackStackEntry). No need to override onCreateView just to force a viewLifecycleOwner to be created or anything!

Solution 4

this happens because the lifecycle of DialogFragment is different from Fragment; onCreateDialog is called before onCreateView, so viewLifecycleOwner is unavailable... I worked around the issue by:

• implemeting onCreateView instead of onCreateDialog
  • can access viewLifecycleOwner from within onCreateView
  • view returned from onCreateView is put into a dialog for us by DialogFragment...
  • you will need to create your own buttons, and titles in the dialog...

supplemental code:

class TextInputDialogFragment : DialogFragment() {

    ...

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?
    ): View? {
        val viewBinding = FragmentDialogTextInputBinding.inflate(layoutInflater, container, false)

        val titleText = params.title.localize(requireContext())
        viewBinding.toolbar.isVisible = titleText.isNotBlank()
        if (titleText.isNotBlank()) {
            viewBinding.toolbar.title = titleText
        }

        viewBinding.recyclerview.adapter = ListItemAdapter(
            viewLifecycleOwner, requireContext().app.nowFactory, viewModel.fields
        )

        viewBinding.buttonAffirm.setOnClickListener {
            listener.onOkPressed(viewModel.userInputtedText.value)
            dismiss()
        }

        viewBinding.buttonReject.setOnClickListener {
            dismiss()
        }

        viewModel.enablePositiveButton.observe(viewLifecycleOwner) { isEnabled ->
            viewBinding.buttonAffirm.isEnabled = isEnabled
        }

        return viewBinding.root
    }

    ...
}

the layout file used

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res-auto">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">

        <androidx.appcompat.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:minHeight="?attr/actionBarSize"
            tools:title="Title" />

        <androidx.recyclerview.widget.RecyclerView
            android:id="@+id/recyclerview"
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:layout_weight="1"
            app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager" />

        <LinearLayout
            style="?buttonBarStyle"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:clickable="false"
            android:gravity="end"
            android:orientation="horizontal"
            android:padding="@dimen/min_touch_target_spacing_half">

            <Button
                android:id="@+id/button_reject"
                style="?buttonBarButtonStyle"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_margin="@dimen/min_touch_target_spacing_half"
                android:text="@android:string/cancel" />

            <Button
                android:id="@+id/button_affirm"
                style="?buttonBarButtonStyle"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_margin="@dimen/min_touch_target_spacing_half"
                android:text="@android:string/ok" />

        </LinearLayout>

    </LinearLayout>

</layout>

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