app/src/main/res/layout/activity_chat.xml

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

    <android.support.v7.widget.RecyclerView
        android:id="@+id/recyclerViewChat"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"/>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <EditText
            android:id="@+id/input_text"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:hint="@string/message_input_hint"
            android:inputType="text"/>
        <Button
            android:id="@+id/select_func"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/select_func"/>
        <Button
            android:id="@+id/button_send"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/send_button_text"/>
    </LinearLayout>

</LinearLayout>