With introduction of ConstraintLayout you don’t have to write either a single line of code or use third-parties or rely on PercentFrameLayout which were deprecated in 26.0.0.
Here’s the example of how to keep 1:1 aspect ratio for your layout using ConstraintLayout:
<android.support.constraint.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<FrameLayout
android:layout_width="0dp"
android:layout_height="0dp"
android:layout_marginEnd="0dp"
android:layout_marginStart="0dp"
android:layout_marginTop="0dp"
android:background="@android:color/black"
app:layout_constraintDimensionRatio="H,1:1"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent">
</FrameLayout>
</android.support.constraint.ConstraintLayout>
Or instead of editing your XML file, you can edit your layout directly in Layout Editor:
