MaterialCardView with MaterialShapeDrawable

Question

I want to achieve this:

So I thought I could use a MaterialShapeDrawable to apply that transformation:

binding.card.background = MaterialShapeDrawable(
    ShapeAppearanceModel.builder()
        .setAllCornerSizes(5.dpToPx().toFloat())
        .setTopEdge(object : TriangleEdgeTreatment(7.dpToPx().toFloat(), false){
            override fun getEdgePath(length: Float, center: Float, interpolation: Float, shapePath: ShapePath) {
                super.getEdgePath(length, 12.dpToPx().toFloat(), interpolation, shapePath)
            }
        })
        .build()
).apply {
    fillColor = resourcesProvider().colorStateListFromAttr(R.attr.colorSurface, R.style.App_CardView)
}

But unfortunately it changes nothing. So I've tried to apply to a direct children like this:

<com.google.android.material.card.MaterialCardView
    style="@style/Widget.MaterialComponents.CardView"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_marginStart="20dp"
    android:layout_marginTop="5dp"
    android:layout_marginEnd="20dp"
    android:clipChildren="false"
    app:cardBackgroundColor="@android:color/transparent"
    app:cardElevation="10dp">

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="100dp"
        android:layout_marginTop="10dp"> //without this margin nothing is shown

And it kinda works but I get a funky result due to app:cardElevation="10dp" (which is needed):

So my questions are:
1 - Is it possible to apply transformations to a CardView? if so, how?
2 - How can I solve this "shadow on top" problem?

Thanks.

Answer 1

Since you are drawing outside the CardView, in the parent view you should use something like:

  <LinearLayout
      android:clipChildren="false"
      android:clipToPadding="false"
      android:padding="16dp"
      ..>

        <com.google.android.material.card.MaterialCardView
         app:cardElevation="2dp"
         ../>

Then apply the changes to ShapeAppearanceModel but getting the existing ShapeAppearanceModel used by the cardview (in your code you are replacing the existing MaterialShapeDrawable not only applying a change in the ShapeAppearanceModel):

cardView.setShapeAppearanceModel(cardView.getShapeAppearanceModel()
        .toBuilder()
        .setTopEdge(new TriangleEdgeTreatment(size, false){

            @Override public void getEdgePath(float length, float center, float interpolation,
              @NonNull ShapePath shapePath) {
              //...... your implementation
            }
          }
        )
        .build());

Starting with the 1.2.0-beta01 you can also use the OffsetEdgeTreatment with a MarkerEdgeTreatment.

Something like:

MarkerEdgeTreatment markerEdgeTreatment = new MarkerEdgeTreatment(size);
OffsetEdgeTreatment offsetEdgeTreatment = new OffsetEdgeTreatment(markerEdgeTreatment,offset);

cardView.setShapeAppearanceModel(cardView.getShapeAppearanceModel()
            .toBuilder()
            .setTopEdge(offsetEdgeTreatment)
            .build());