AppBarLayout.ScrollingViewBehavior - bottom of view off screen

Question

When using an AppBarLayout with the standard ScrollingViewBehavior, the AppBarLayout's sibling will by default be the height of the CoordinatorLayout and the sibling's bottom will be offscreen by the height of the AppBarLayout.

In my use case, the NestedScrollView is merely a vehicle to allow for the collapsing of the toolbar, while displaying another scrollable view (fragment in this case) beneath the collapsible toolbar. The fragment is the one who contains the bottom-pinned view (FAB in this case)

Pictures below demonstrate the issue I am describing, and the code supplied is the basic XML which causes the issue.

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
    android:id="@+id/coordinatorLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:android="http://schemas.android.com/apk/res/android">

    <android.support.design.widget.AppBarLayout
        android:id="@+id/appBarLayout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            app:layout_scrollFlags="scroll|enterAlways" />

    </android.support.design.widget.AppBarLayout>

    <android.support.v4.widget.NestedScrollView
        android:id="@+id/nestedScrollView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="@string/appbar_scrolling_view_behavior">

        <LinearLayout
            android:id="@+id/fragmentHolder"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="vertical">

        </LinearLayout>

    </android.support.v4.widget.NestedScrollView>

</android.support.design.widget.CoordinatorLayout>

Answer 1

The solution I found to this issue involves 2 parts.

1. Add padding equal to the height of the AppBarLayout to the BOTTOM of the NestedScrollView. In my case because the AppBarLayout only contained a Toolbar, the height was ?attr/actionBarSize.
   android:paddingBottom="?attr/actionBarSize"

2. Adding a custom AppBarLayout.OnOffsetChangedListener to the AppBarLayout which changes the height of the NestedScrollView as the toolbar is collapsed.

   class ScrollingOffsetFixListener(
       private val nestedScrollView: NestedScrollView
   ): AppBarLayout.OnOffsetChangedListener {
   
   private var originalHeight = 0
   private var firstOffset = true
   
   override fun onOffsetChanged(layout: AppBarLayout?, offset: Int) {
       if(firstOffset) {
           firstOffset = false
           originalHeight = nestedScrollView.measuredHeight
       }
   
       val params = nestedScrollView.layoutParams
       params.height = originalHeight + (offset * -1)
   
       nestedScrollView.layoutParams = params
      }
   }