How do I delay the mutation of a struct in SwiftUI? - swiftui

Question

I'm coding my app in SwiftUI, and am trying to follow their declarative conventions but I'm coming a little unstuck.
I have a data model which is passed down through the view hierarchy using Bindings, and one of my child views has the ability to change a few of the properties on the Model to trigger a layout change.
Because its animations are a function of the data, I need to stagger the change to the model to get the animation I want. Here's a simple example; assume I need to clear the contents of the child view for architectural reasons. What's the best way to get the content to draw in to the red panel before ChildView animates up, and then when dismissed, wait until the animation is finished before removing the content?
struct ContentView: View {
#State var contents: [String] = ["A", "B", "C", "A", "B", "C", "A", "B", "C"]
#State var showingPanel: Bool = false
var body: some View {
VStack {
HStack {
Button(action: {
self.contents = ["A", "B", "C", "A", "B", "C", "A", "B", "C"]
self.showingPanel = true
}) {
Text("Show Panel")
}
Button(action: {
self.showingPanel = false
DispatchQueue.main.asyncAfter(deadline: .now() + 2) {
self.contents = []
}
}) {
Text("Clear Panel")
}
}
ChildView(showingPanel: $showingPanel, contents: $contents)
}
}
}
struct ChildView: View {
#Binding var showingPanel: Bool
#Binding var contents: [String]
var body: some View {
ZStack {
Color.red
VStack {
ForEach(contents, id: \.self) { content in
Text(content).font(.title)
}
}.animation(nil)
}.offset(y: showingPanel ? 0 : UIScreen.main.bounds.size.height).animation(.default)
}
}
My first stab was to use the DispatchQueue to try and delay the change, but that doesn't look right and also doesn't work!