How to make SwiftUI to forget internal state - swiftui

Question

I have a view like following
struct A: View {
var content: AnyView
var body: some View {
ScrollView(.vertical, showsIndicators: false) {
VStack {
// Common Elements
content
// More Common Elements
}
}
}
}
When I call this from another view like
A(nextInnerView())
two things happen. Firstly, as the size of the content element changes ScrollView animates the transition. Secondly, if you scroll down and then change the content the scrolling position does not reset.

Answer 1

Here is a demo of possible solution. Tested with Xcode 11.4 / iOS 13.4
The origin of this behaviour is in SwiftUI rendering optimisation, that tries to re-render only changed part, so approach is to identify view A (to mark it as completely changed) based on condition that originated in interview changes, alternatively it can be identified just by UUID().
struct TestInnerViewReplacement: View {
#State private var counter = 0
var body: some View {
VStack {
Button("Next") { self.counter += 1 }
Divider()
A(content: nextInnerView())
.id(counter) // << here !!
}
}
private func nextInnerView() -> AnyView {
AnyView(Group {
if counter % 2 == 0 {
Text("Text Demo")
} else {
Image(systemName: "star")
.resizable()
.frame(width: 100, height: 100)
}
})
}
}
struct A: View {
var content: AnyView
var body: some View {
ScrollView(.vertical, showsIndicators: false) {
VStack {
ForEach(0..<5) { _ in // upper content demo
Rectangle().fill(Color.yellow)
.frame(height: 40)
.frame(maxWidth: .infinity)
.padding()
}
content
ForEach(0..<10) { _ in // lower content demo
Rectangle().fill(Color.blue)
.frame(height: 40)
.frame(maxWidth: .infinity)
.padding()
}
}
}
}
}