如何在AbsoluteLayout中的控件上设置z索引？

<AbsoluteLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Button 1" />

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Button 2" />

</AbsoluteLayout>

AbsoluteLayout layout = findViewById(R.id.absoluteLayout);
Button button1 = findViewById(R.id.button1);
Button button2 = findViewById(R.id.button2);

// 将button1置于顶层
button1.bringToFront();

// 将button2置于顶层
button2.bringToFront();