fragment_main.xml

<FrameLayout 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"
    tools:context="com.example.android.digitalhome.MainFragment">

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:paddingBottom="@dimen/activity_vertical_margin"
        android:paddingLeft="@dimen/activity_horizontal_margin"
        android:paddingRight="@dimen/activity_horizontal_margin"
        android:paddingTop="@dimen/activity_vertical_margin">

    <TextView
        android:text="Main Switch"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="#757575"
        android:textColor="#ffffff"
        android:id="@+id/textView"
        android:textAppearance="@style/TextAppearance.AppCompat.Display1"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true" />

    <ToggleButton
        android:text="ToggleButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/textView"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="12dp"
        android:id="@+id/mtoggleButton1" />

    <Button
        android:text="Light"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="41dp"
        android:id="@+id/blight"
        android:layout_below="@+id/mtoggleButton1"
        android:layout_alignStart="@+id/mtoggleButton1" />

    <Button
        android:text="Fan"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/blight"
        android:layout_alignEnd="@+id/blight"
        android:layout_marginTop="42dp"
        android:id="@+id/bfan" />

        <Button
            android:text="Logout"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_below="@+id/bfan"
            android:layout_alignEnd="@+id/bfan"
            android:layout_marginTop="42dp"
            android:id="@+id/blogout" />
    </RelativeLayout>

</FrameLayout>