keep screen awake while in foreground

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

@@ -8,6 +8,7 @@
     android:paddingLeft="@dimen/activity_horizontal_margin"
     android:paddingRight="@dimen/activity_horizontal_margin"
     android:paddingTop="@dimen/activity_vertical_margin"
+    android:keepScreenOn="true"
     tools:context=".MainActivity"
     android:orientation="vertical">