The solution is just to make height animatable continuously, by providing explicit animatable modifier for this.
Here is working approach. Tested with Xcode 11.4 / iOS 13.4.
Implementation of simple helper modifier
struct AnimatingCellHeight: AnimatableModifier {
var height: CGFloat = 0
var animatableData: CGFloat {
get { height }
set { height = newValue }
}
func body(content: Content) -> some View {
content.frame(height: height)
}
}
Modified using view (other parts unchanged)
struct SubView: View {
@State var change: Bool = false
var body: some View {
Rectangle()
.frame(width: 200)
.modifier(AnimatingCellHeight(height: change ? 300 : 200))
.foregroundColor(Color.red)
.onTapGesture {
withAnimation {
self.change.toggle()
}
}
}
}