[CollapsingToolbarLayout] Consuming system window insets blocks sibling views from receiving insets

Description: CollapsingToolbarLayout is listening to window insets and inside the listener calls:

// Consume the insets. This is done so that child views with fitSystemWindows=true do not
// get the default padding functionality from View
return insets.consumeSystemWindowInsets();

While consuming the insets, so its children do not receive them makes sense, due to how insets are dispatched by system, this causes insets to not be dispatched also to its sibling views.

Maybe it could only consume the insets only if android:fitsSystemWindows="true"?

After quite some trial & error I discovered a workaround: if I set my own insets listener (doing nothing) on the CollapsingToolbarLayout, I can avoid it consuming the insets. But this feels like hacking around it instead of proper solution.

Expected behavior: System window insets are also dispatched to its sibling views.

Source code:

<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <com.google.android.material.appbar.AppBarLayout
        android:id="@+id/appBar"
        android:layout_width="match_parent"
        android:layout_height="160dp">

        <com.google.android.material.appbar.CollapsingToolbarLayout
            android:id="@+id/collapsingToolbar"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:layout_scrollFlags="scroll|exitUntilCollapsed|snap">

            <com.google.android.material.appbar.MaterialToolbar
                android:layout_width="match_parent"
                android:layout_height="?attr/actionBarSize"
                app:layout_collapseMode="pin" />

    </com.google.android.material.appbar.CollapsingToolbarLayout>

    </com.google.android.material.appbar.AppBarLayout>

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recyclerView"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</androidx.coordinatorlayout.widget.CoordinatorLayout>

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    ViewCompat.setOnApplyWindowInsetsListener(recyclerView) { _, insets ->
        // this will not be called
        insets
    }

    ViewCompat.setOnApplyWindowInsetsListener(appBar) { _, insets ->
        // this is called ok
        insets
    }
}

Android API version: I checked on api 29.

Material Library version: 1.1.0, 1.2.0-alpha06

[bompf]

I also stumbled over this on version 1.2.0-alpha04. A OnApplyWindowInsetsListener on BottomNavigationView would not be called anymore as soon as I navigate to a view containing CollapsingToolbarLayout, resulting in the BottomNavView being occluded by the system navigation bar.

My current workaround is opting out of the consuming behavior by removing the listener on the CollapsingToolbarLayout:

ViewCompat.setOnApplyWindowInsetsListener(collapsingToolbarLayout, null)

Would be great if this issue could be resolved.

[Flamedek]

Very confusing behaviour to encounter. Though the provided workaround does work.

When targeting API 30+ and using the new WindowsInsetsCompat and WindowInsetsControllerCompat API, this behaviour is only seen when the legacy implementation is used (up to API 29) and not on API 30+.
This is extra worrying as developers use a single API and expect similar behavior on all devices.

The proposed changed to only do this with fitsSystemWindows="true" seems good, as it’s available as opt-in when needed but does cause this unexpected issue by default.