activity_chat.xml

<?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"
    tools:context=".Chat">

    <!-- A horizontal line between the chatbox and RecyclerView -->
    <View
        android:id="@+id/view"
        android:layout_width="0dp"
        android:layout_height="2dp"
        android:background="#dfdfdf"
        app:layout_constraintBottom_toTopOf="@+id/layout_chatbox"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent" />

    <LinearLayout
        android:id="@+id/layout_chatbox"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        android:minHeight="48dp"
        android:background="#ffffff"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintLeft_toLeftOf="parent">

        <EditText
            android:id="@+id/edittext_chatbox"
            android:hint="Enter message"
            android:background="@android:color/transparent"
            android:layout_gravity="center"
            android:layout_marginLeft="16dp"
            android:layout_marginRight="16dp"
            android:layout_width="0dp"
            android:layout_weight="1"
            android:layout_height="wrap_content"
            android:maxLines="6"/>

        <Button
            android:id="@+id/button_chatbox_send"
            android:text="SEND"
            android:textSize="14dp"
            android:textColor="@android:color/white"
            android:background="@drawable/circle"
            android:clickable="true"
            android:layout_width="64dp"
            android:layout_height="48dp"
            android:gravity="center"
            android:layout_gravity="bottom" />

    </LinearLayout>

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/rv"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_marginBottom="2dp"
        app:layout_constraintBottom_toTopOf="@+id/view"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>