How to set child view size based on parent size?

I made a custom ViewGroup which has one child view. I want this child view height to be calculated based on the custom ViewGroup height. As far as I know the best place to detect the ViewGroup size is onSizeChanged callback so I put there a code responsible for changing child view size. Unfortunately, this doesn't work. Nothing changes.

class CustomViewGroup(context: Context, attrs: AttributeSet?) : ConstraintLayout(context, attrs) {

    private val imageView = ImageView(context).apply {
        id = ViewCompat.generateViewId()
        setImageDrawable(ColorDrawable(Color.BLUE))
        layoutParams = LayoutParams(100, 100)
    }

    init {
        addView(imageView)
        with(ConstraintSet()) {
            clone(this@CustomViewGroup)
            connect(imageView.id, ConstraintSet.START, id, ConstraintSet.START)
            connect(imageView.id, ConstraintSet.TOP, id, ConstraintSet.TOP)
            connect(imageView.id, ConstraintSet.END, id, ConstraintSet.END)
            connect(imageView.id, ConstraintSet.BOTTOM, id, ConstraintSet.BOTTOM)
            applyTo(this@CustomViewGroup)
        }
    }

    override fun onSizeChanged(w: Int, h: Int, oldw: Int, oldh: Int) {
        super.onSizeChanged(w, h, oldw, oldh)
        imageView.updateLayoutParams { height = h / 4 } //some complex equation
    }
}

<com.example.customviewgroup1.CustomViewGroup
            android:id="@+id/customViewGroup"
            android:layout_width="match_parent"
            android:layout_height="300dp"
            android:background="@color/black"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />