Android - ConstraintLayout set Percent Height programmatically?

Question

here is my layout :

...
<android.support.constraint.ConstraintLayout   
android:layout_width="0dp"
android:layout_height="match_parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintWidth_percent="0.6"
>
            <android.support.constraint.ConstraintLayout
                android:id="@+id/myclayout"
                android:layout_width="match_parent"
                android:layout_height="0dp"
                app:layout_constraintHeight_percent="0.2"
                app:layout_constraintTop_toTopOf="parent"
                ></android.support.constraint.ConstraintLayout>


 </android.support.constraint.ConstraintLayout>
...

how to set constraintHeight_percent programmatically ?

I tried with ConstraintSet but did not work

ConstraintSet set = new ConstraintSet();
set.constrainPercentHeight(R.id.myclayout, (float) 0.4);
set.applyTo(((ConstraintLayout) vw.findViewById(R.id.myclayout)));

Answer 1

the right answer is :

    ConstraintLayout mConstrainLayout  = (ConstraintLayout) vw.findViewById(R.id.myclayout);
    ConstraintLayout.LayoutParams lp = (ConstraintLayout.LayoutParams) mConstrainLayout.getLayoutParams();
    lp.matchConstraintPercentHeight = (float) 0.4;
    mConstrainLayout.setLayoutParams(lp);

Answer 2

I went with using a ConstraintSet to update the width and height of a ConstraintLayout's child:

        val set = ConstraintSet()
        set.clone(parentLayout) // parentLayout is a ConstraintLayout
        set.constrainPercentWidth(childElement.id, .5f)
        set.constrainPercentHeight(childElement.id, .5f)
        set.applyTo(parentLayout)

...the float values should be a percentage mapped to the unit interval.