Unknown attribute class warning with FragmentContainerView

Question

I have a SettingsFragment class that hosts a PreferenceFragment for the app settings.

In layout, I used FragmentContainerView which points to that PreferenceFragment class with the class attribute.

<androidx.fragment.app.FragmentContainerView
    class="xxxxxx.fragments.SettingsFragment$PreferenceFragment"
    android:layout_width="match_parent"
    android:layout_height="match_parent"/>

Backing to normal fragment instead of FragmentContainerView the warning is gone, so it turns out that it's related to FragmentContainerView.

How can I get rid of this warning while using FragmentContainerView?

Answer 1

It should be android:name="xxxxxx.fragments.SettingsFragment$PreferenceFragment" as per FragmentContainerView documentation.

<androidx.fragment.app.FragmentContainerView
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:id="@+id/fragment_container_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:name="xxxxxx.fragments.SettingsFragment$PreferenceFragment"
        android:tag="my_tag">
 </androidx.fragment.app.FragmentContainerView>
 

Answer 2

Unknown fragments error solution for Android Studio 2022.1.1 Patch 1 (Electric Eel):

Click the red icon with exclamation mark.

In bottom panel with errors found in layout, select Unknown fragments.

In right part of bottom panel, click the link Do not warn about <android.fragment.app. FragmentContainerView> tags in this session

Congratulations! Your layout preview is now working again!

NOTE: Sadly, this solution only works until you close Android Studio. If anyone knows about permanent solution, please let me know in comments and I will update this answer.

Answer 3

For Unknown fragments error solution for Android Studio 2022.1.1 Patch 1 (Electric Eel):

use this:

<androidx.fragment.app.FragmentContainerView
    android:id="@+id/fragment_container_view"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:name="xxxxxx.xxxxxx.FragmentName"
    tools:layout="@layout/fragment_name"
/>

Remember, add the tools:layout...