activity_main.xml
<android.support.percent.PercentRelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" android:layout_width="match_parent" android:layout_height="match_parent">
<Button
android:id="@+id/button1"
android:text="Button 1"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
app:layout_widthPercent="50%"
app:layout_heightPercent="50%"
/>
<Button
android:id="@+id/button2"
android:text="Button 2"
android:layout_alignParentRight="true"
android:layout_alignParentTop="true"
app:layout_widthPercent="50%"
app:layout_heightPercent="50%"
/>
<Button
android:id="@+id/button3"
android:text="Button 3"
android:layout_alignParentLeft="true"
android:layout_alignParentBottom="true"
app:layout_widthPercent="50%"
app:layout_heightPercent="50%"
/>
<Button
android:id="@+id/button4"
android:text="Button 4"
android:layout_alignParentRight="true"
android:layout_alignParentBottom="true"
app:layout_widthPercent="50%"
app:layout_heightPercent="50%"
/>
</android.support.percent.PercentRelativeLayout>