activity_main_chat.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/rvChat"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="8"
        android:background="#e3e3e3" />


    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="2">

        <EditText
            android:id="@+id/etMessage"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1" />

        <Button
            android:id="@+id/btnSend"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Kirim" />
    </LinearLayout>

</LinearLayout>