如何访问波纹内的形状以修改可绘制的颜色？

Question

<?xml version="1.0" encoding="utf-8"?><!-- in drawable folder-->
<layer-list xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools">

    <item android:id="@+id/ripple">
        <ripple android:color="?android:attr/colorControlHighlight">
            <item android:id="@+id/shape">
                <shape>
                    <solid android:color="@color/payments_blue" />
                    <corners android:radius="50dp" />
                </shape>
            </item>
        </ripple>
    </item>
</layer-list>

val layerDrawable = btnGoomer.background as LayerDrawable
val ripple = layerDrawable.findDrawableByLayerId(R.id.ripple) as RippleDrawable
val shape = ripple.findDrawableByLayerId(R.id.shape) as ShapeDrawable

当我尝试在这个 drawable 中引用形状时，我能够找到波纹但找不到形状，我做错了什么？谢谢