Dynamic content hight in VStack SwiftUI - swift

Question

Why I can't dynamically change content in VStack if I don't have a lot objects in ScrollView? What is surprising, if there are a lot of objects, then everything changes beautifully, but if there are few, then the scroll only works down (because of this, there may be glitches when trying to scroll up)
My code:
import Introspect
struct SwiftUIView: View {
#StateObject var myCoord = MyCoord()
var body: some View {
VStack {
Color.red
.frame(height: myCoord.height)
ScrollView {
ForEach(0..<20) { _ in
Color.green
.frame(height: 20)
}
.background(Color.red)
}
.introspectScrollView { scroll in
scroll.delegate = myCoord
}
}
}
}
class MyCoord: NSObject, UIScrollViewDelegate, ObservableObject {
let maxSize: CGFloat = 76
let minSize: CGFloat = 56
#Published var height: CGFloat = 76
func scrollViewDidScroll(_ scrollView: UIScrollView) {
let size = maxSize - scrollView.contentOffset.y
height = min(maxSize, max(minSize, size))
}
}

Answer 1

ScrollView
Solved was putt all view in ZStack and add some fake views in Scroll view.
1 view is responsible for the size where the scroll cannot fall through.
2 view is responsible for the size between the maximum and minimum size of the header
Here's a examples
import Introspect
struct ContentView: View {
#StateObject private var myCoord = MyCoord()
var body: some View {
let sizeOfPlaceholder = myCoord.maxSize - myCoord.minSize
ZStack(alignment: .top) {
VStack(spacing: 0) {
Color.black
.frame(height: myCoord.minSize)
ScrollView {
Color.brown
.frame(height:sizeOfPlaceholder)
ForEach(0..<20) { number in
Text("\(number)")
.background(Color.red)
.frame(height: 20)
}
}
.padding(.vertical, 1)
.introspectScrollView { scroll in
scroll.delegate = myCoord
}
}
Color.green
.frame(height: myCoord.height)
}
}
}
class MyCoord: NSObject, UIScrollViewDelegate, ObservableObject {
let maxSize: CGFloat = 76
let minSize: CGFloat = 56
#Published var height: CGFloat = 76
func scrollViewDidScroll(_ scrollView: UIScrollView) {
print(scrollView.contentOffset.y)
let size = maxSize - scrollView.contentOffset.y
height = min(maxSize, max(minSize, size))
}
}