How can I manage this view when constraints aren't available to me in swiftui?

Question

I am very new to SwiftUI, and have actually been getting the hang of arranging my views using the Z, V and HStacks. But the lack of a centre anchor is proving difficult to manage views which need to be anchored to different anchors of other views; as in the following case:

The Blue thing is a popUp and I have anchored the centreY anchor of the button to the bottom anchor of the popUp view, using the following code:

popUpView.centerXAnchor.constraint(equalTo: view.centerXAnchor),
popUpView.topAnchor.constraint(equalTo: view.topAnchor, constant: 100),
popUpView.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: 0.8),
popUpView.heightAnchor.constraint(equalTo: view.heightAnchor, multiplier: 0.45),

myButton.centerXAnchor.constraint(equalTo: popUpView.centerXAnchor),
myButton.centerYAnchor.constraint(equalTo: popUpView.bottomAnchor),
myButton.widthAnchor.constraint(equalTo:   popUpView.widthAnchor, multiplier: 0.285),
myButton.heightAnchor.constraint(equalTo:  popUpView.heightAnchor, multiplier: 0.2),

Is there any way to manage this using stacks in SwiftUI?

Answer 1

If you already have such popUpView and myButton components prepared in SwiftUI, the alignment like on screen can be done actually in two lines

struct ContentView: View {
    var body: some View {
        ZStack(alignment: .bottom) {    // << here !!
            PopUpView()
            MyButton()
                .alignmentGuide(.bottom) { $0.height / 2 } // << here !!
        }
    }
}

Answer 2

The offset will depend on the height of the custom button (I put 20 as example).

struct ContentView: View {
    var body: some View {
        VStack {
            PopUpView()
            MyButton()
                .offset(y: -20)
        }
    }
}