Make SwiftUI Rectangle same height or width as another Rectangle - swift

Question

For a SwiftUI layout in a macOS app, I have three Rectangles as shown below:
The code to produce this layout is:
import SwiftUI
struct ContentView: View {
var body: some View {
VStack {
HStack {
ZStack {
Rectangle()
.fill(Color.purple)
.frame(width: 20)
Text("1")
.font(.subheadline)
.foregroundColor(.white)
}
ZStack {
Rectangle()
.fill(Color.orange)
Text("2")
.font(.subheadline)
.foregroundColor(.white)
}
}
HStack {
ZStack {
Rectangle()
.fill(Color.red)
.frame(height: 20)
Text("3")
.font(.subheadline)
.foregroundColor(.white)
}
}
}
.frame(minWidth: 400, minHeight: 250)
}
}
My objective is for Rectangle 1 to be the same height as Rectangle 2 and for Rectangle 3 to be the same width as Rectangle 2. The size relationships between the rectangles should stay the same as the window size is changed. When done correctly, the final result should look like the following:
How can I accomplish this in SwiftUI?

Answer 1

Here is a working approach, based on view preferences. Tested with Xcode 11.4 / macOS 10.15.6
struct ViewWidthKey: PreferenceKey {
typealias Value = CGFloat
static var defaultValue: CGFloat { 0 }
static func reduce(value: inout Value, nextValue: () -> Value) {
value = value + nextValue()
}
}
struct ContentView: View {
#State private var boxWidth = CGFloat.zero
var body: some View {
VStack {
HStack {
ZStack {
Rectangle()
.fill(Color.purple)
.frame(width: 20)
Text("1")
.font(.subheadline)
.foregroundColor(.white)
}
ZStack {
Rectangle()
.fill(Color.orange)
Text("2")
.font(.subheadline)
.foregroundColor(.white)
}
.background(GeometryReader {
Color.clear.preference(key: ViewWidthKey.self,
value: $0.frame(in: .local).size.width) })
}
HStack {
ZStack {
Rectangle()
.fill(Color.red)
.frame(height: 20)
Text("3")
.font(.subheadline)
.foregroundColor(.white)
}.frame(width: boxWidth)
}.frame(maxWidth: .infinity, alignment: .bottomTrailing)
}
.onPreferenceChange(ViewWidthKey.self) { self.boxWidth = $0 }
.frame(minWidth: 400, minHeight: 250)
}
}