Read view size

ReadSize.swift

import SwiftUI

extension View {
    func readSize(_ reader: @escaping (CGSize) -> Void) -> some View {
        background {
            GeometryReader { geo in
                Color.clear.preference(key: SizeKey.self, value: geo.size)
            }
            .onPreferenceChange(SizeKey.self) { size in
                reader(size)
            }
        }
    }
}

private enum SizeKey: PreferenceKey {
    static let defaultValue: CGSize = .zero

    static func reduce(value: inout Value, nextValue: () -> Value) {
        value = nextValue()
    }
}