SwiftUI : ViewDidLoad & ViewDidAppear

Coming from the UIKit world — there have been multiple callbacks for view lifecycle, when view used to start loading

• viewDidLoad
• viewWillAppear
• viewDidAppear

In SwiftUI — the most closest available callback is onAppear only — which gets called everytime when view is loaded in hierarchy — equivalent to viewDidAppear of UIKit

There comes several use-cases when we need to perform few actions only once while few actions everytime. For this particular requirement — We have a solution -

I have written a viewModifier — which can be appended to any View -

extension View {
    func onViewRenderCycle(didLoadAction: @escaping () -> Void,
                           didAppearAction: (() -> Void)? = nil) -> some View {
        modifier(ViewLifeCycleModifier(didLoadAction: didLoadAction, 
                                     didAppearAction: didAppearAction))
    }
}

struct ViewLifeCycleModifier: ViewModifier {
    let didLoadAction: () -> Void
    let didAppearAction: (() -> Void)?

    @State
    private var appeared = false

    func body(content: Content) -> some View {
        content.onAppear {
            if !appeared {
                appeared = true
                didLoadAction()
            } else {
                didAppearAction?()
            }
        }
    }
}

On your View Structs — simply append onViewRenderCycle method to receive different callbacks for first time & subsequent view render cycles

struct MainView : View {
    var body: some View {
        VStack{
            Text("Hello World")
        }
        .onViewRenderCycle {
            // ViewDidLoad - FirstTime
        } didAppearAction: {
            // ViewDidAppear - Subsequent Times
        }

    }
}