OnLayout Tutorial 10

OnLayout Tutorial 10.swift

struct LayoutActionModifier: ViewModifier {
  
    /// This action is run after each time the view changes.
    let action: ((GeometryProxy) -> Void)?
  
    func body(content: Content) -> some View {
        content
            .background(
                GeometryReader { proxy in
                    layoutWatcher(proxy)
                }
            )
    }
  
    func layoutWatcher(_ proxy: GeometryProxy) -> some View {
        /// This runs the action after each time the view is 
        /// updated.
        DispatchQueue.main.async {
            action?(proxy)
        }
        let result = Color.clear
            /// This runs the action when the view first appears.
            .onAppear {
                action?(proxy)
            }
        return result
    }
}

extension View {
    func onLayout(
        perform action: ((GeometryProxy) -> Void)? = nil
    ) -> some View {
        self.modifier(LayoutActionModifier(action: action))
    }
}