How can I force an empty ConstraintLayout to fill its parent container?

Question

I am using a ConstraintLayout as an overlay. It should be as wide and as tall as its parent container. However, for some strange reason it does not fill its parent vertically (but does horizontally). Here is the relevant XML:

<androidx.constraintlayout.widget.ConstraintLayout 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"
    tools:context=".ui.home.HomeFragment">

    <androidx.constraintlayout.widget.ConstraintLayout  <-- This is the overlay
        android:id="@+id/overlay"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="#80000000"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

With the above code the overlay is not visible either (its height is 0dp). When I place a TextView inside, it expands to fit the TextView. In short, it is behaving as if its height was set to wrap_content.

How do I force it to fill its container while leaving it empty?

Answer 1

The problem is most likely your size specifications. From the documentation for ConstraintLayout:

Important: MATCH_PARENT is not recommended for widgets contained in a ConstraintLayout. Similar behavior can be defined by using MATCH_CONSTRAINT with the corresponding left/right or top/bottom constraints being set to "parent".

There really should be a lint rule for this or ConstraintLayout should reject match_parent.