BottomSheetDialog with ConstraintLayout containing NestedScrollView having height match_constraint rendered with actual 0px height

I have a very simple layout that I need to render into a BottomSheetDialog. The layout is just a scrolling view containing just TextViews and a button below the scrolling view (so the button is fixed at the bottom and always visible.) This is just a distilled version of what's in my app, but it will suffice to explain the problem:

<?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"
    android:layout_height="match_parent"
    android:layout_width="match_parent">

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <androidx.core.widget.NestedScrollView
            android:id="@+id/nestedScrollView"
            android:fillViewport="true"
            android:layout_width="0dp"
            android:layout_height="0dp"
            android:layout_marginBottom="16dp"
            app:layout_constraintBottom_toTopOf="@id/ok_button"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent">

        <androidx.constraintlayout.widget.ConstraintLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent">

                <TextView
                    android:id="@+id/fine_print_header"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:layout_marginStart="16dp"
                    android:layout_marginLeft="16dp"
                    android:layout_marginTop="32dp"
                    android:layout_marginEnd="16dp"
                    android:gravity="center_horizontal"
                    android:text="Fine Print"
                    app:layout_constraintEnd_toEndOf="parent"
                    app:layout_constraintStart_toStartOf="parent"
                    app:layout_constraintTop_toTopOf="parent" />

                <TextView
                    android:id="@+id/fine_print_copy"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:layout_marginStart="16dp"
                    android:layout_marginLeft="16dp"
                    android:layout_marginTop="32dp"
                    android:layout_marginEnd="16dp"
                    android:text="This is the fine print. It's very detailed. So many carefully crafted details"
                    app:layout_constraintEnd_toEndOf="parent"
                    app:layout_constraintStart_toStartOf="parent"
                    app:layout_constraintTop_toBottomOf="@id/fine_print_header"/>

            </androidx.constraintlayout.widget.ConstraintLayout>
        </androidx.core.widget.NestedScrollView>
        <Button
            android:id="@+id/ok_button"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_marginHorizontal="16dp"
            android:layout_marginVertical="16dp"
            android:text="OK"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@id/nestedScrollView"/>
    </androidx.constraintlayout.widget.ConstraintLayout>>
</androidx.coordinatorlayout.widget.CoordinatorLayout>

Here is how I present the layout in my Fragment code:

            val contentView = requireActivity().layoutInflater.inflate(R.layout.bottom_sheet_dialog, null)
            val bottomSheetDialog = BottomSheetDialog(requireContext())
            bottomSheetDialog.setContentView(contentView)
            bottomSheetDialog.show()

What I am expecting to see is what is in the preview in Android Studio:

What I actually see is this:

If I step in with Layout Inspector, I can see that the NestedScrollView is really there, but it is rendered with height 0px. It's as if the constraint layout tooling ignored the whole match_constraint idea and really rendered things as if I called for 0dp. If I use match_parent it will render behind the button; if I use wrap_content the preview shows it rendering outside the bounds. If I set an actual size (e.g. 80dp) then it will appear: but this is not a scalable solution – I should be able to use match_constraint here!

I tried all the relevant combinations of top:bottom constraint relationships between the NestedScrollView and the Button, tried with and without android:fillViewPort="true", tried with and without app:layout_behavior=“@string/appbar_scrolling_view_behavior”, tried without using a CoordinatorLayout as the top layout (using a ConstraintLayout at the top instead) – none of these have ANY effect whatsoever.

Anyone know how to deal with this?

UPDATE:

I was able to make something work (without having to "concede defeat" and switch to RelativeLayout.) On the NestedScrollView I set:

            android:layout_height="wrap_content"
            app:layout_constrainedHeight="true"

and now it renders correctly in both the preview and the device.

I would still like to know why MATCH_CONSTRAINT isn't working in this context.

UPDATE:

Recommended topics

Hot tags