ConstraintLayout drawing order/layer order

Question

Simple question:

What is the exact algorithm used by ConstraintLayout in order to know which View is drawn first and which View is drawn last?

In RelativeLayout, the last View in the XML file is drawn last, hence it will be on top of everything, obscuring the Views which where drawn earlier.

Why does not ConstraintLayout carry the same function (at least, apparently)?

The following code results in the Button being displayed on top of the included View.

<Button
    android:id="@+id/calculate"
    android:layout_width="183dp"
    android:layout_height="76dp"
    android:layout_marginBottom="5dp"
    android:layout_marginLeft="16dp"
    android:layout_marginStart="16dp"
    android:text="C A L C U L A T E"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintLeft_toLeftOf="parent" />

<include
    android:id="@+id/help_window"
    layout="@layout/help_window"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_alignParentBottom="true"
    android:layout_alignParentLeft="true"
    android:layout_alignParentStart="true"
    android:layout_marginBottom="0dp"
    android:layout_marginLeft="0dp"
    android:layout_marginRight="0dp"
    android:layout_marginTop="0dp"
    android:visibility="invisible"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/include4" />


</android.support.constraint.ConstraintLayout>

Answer 1

Alright. I solved this now.

Apparently buttons are treated seperately. With a buildt in elevation to alwyas be on top.

solution is to remove this elevation, write this in the xml file in your button:

android:stateListAnimator="@null"