androidx Recycler View match constraint (0dp) with wrap content behaviour

Question

I have simple recycler view here, what I want is:

when list is short: stick the button below the recycler view

when list is long: stick the button bottom of screen yet recycler view is wrapping properly and able to scroll till bottom

<?xml version="1.0" encoding="utf-8"?>
<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">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/rv_user_address"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginStart="20dp"
        android:layout_marginTop="15dp"
        android:layout_marginEnd="20dp"
        app:layout_constraintBottom_toTopOf="@id/btn"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_chainStyle="packed"
        app:layout_constraintVertical_bias="0.0"
        tools:itemCount="50"/>

    <Button
        android:id="@+id/btn"
        android:layout_width="match_parent"
        android:layout_height="40dp"
        android:layout_marginStart="20dp"
        android:layout_marginTop="20dp"
        android:layout_marginEnd="20dp"
        android:layout_marginBottom="20dp"
        android:text="example"
        android:background="#00ffff"
        android:gravity="center"
        android:orientation="horizontal"
        app:layout_constraintTop_toBottomOf="@id/rv_user_address"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintBottom_toBottomOf="parent"/>

</androidx.constraintlayout.widget.ConstraintLayout>

When is wrap_content:

<androidx.recyclerview.widget.RecyclerView
android:layout_height="wrap_content"
...

short-list can stick button below properly but button is off screen when list is long

When is constraint:0dp:

<androidx.recyclerview.widget.RecyclerView
android:layout_height="0dp"
...

long list is correct behavior but short-list not stick button below list

I am out of idea. Thanks for helping.

Answer 1

Just add this line:

app:layout_constrainedHeight="true"

to your Recyclerview as:

<androidx.recyclerview.widget.RecyclerView
        android:id="@+id/rv_user_address"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="20dp"
        android:layout_marginTop="15dp"
        android:layout_marginEnd="20dp"
        app:layout_constrainedHeight="true"   <--  Add this line
        app:layout_constraintBottom_toTopOf="@id/btn"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_chainStyle="packed"
        app:layout_constraintVertical_bias="0.0"
        tools:itemCount="50"/>