Measures the size of any view

View+MeasureSize.swift

import SwiftUI

struct MeasureSizeModifier: ViewModifier {
    @Binding var size: CGSize

    func body(content: Content) -> some View {
        content.background {
            GeometryReader { geometry in
                Color.clear
                    .onAppear { size = geometry.size }
                    .onChange(of: geometry.size) { size = geometry.size }
            }
        }
    }
}

extension View {
    func measure(size: Binding<CGSize>) -> some View {
        modifier(MeasureSizeModifier(size: size))
    }
}

struct ContentView: View {
    @State var size: CGSize = .zero

    var body: some View {
        VStack {
            ⋮ 
        }
        .measure(size: $size)
    }
}