ActionNavigationLink

ActionNavigationLink.swift

//
//  Created by Kris McGinnes on 2/6/20.
//  Copyright © 2020 Spicy Taco. All rights reserved.
//

import SwiftUI

/// A type that allows future navigation within an `ActionNavigationLink` context.
struct NavigationToken {
    private let navigationAction: () -> ()

    fileprivate init(_ action: @escaping () -> ()) {
        self.navigationAction = action
    }

    /// Performs navigation immediately.
    func navigate() {
        navigationAction()
    }
}

/// Similar to a normal `NavigationLink`, but allows arbitrary code to be executed before explicitly allowing navigation to proceed.
///
/// This allows delays to be added, models to be updated, or conditionals to be checked before performing, or not performing, the actual naviation.
struct ActionNavigationLink<Destination: View, Content: View>: View {
    private let destination: Destination
    private let content: Content
    private let action: (NavigationToken) -> ()

    @State private var continueToDestination: Bool = false

    init(
        destination: Destination,
        action: @escaping (NavigationToken) -> (),
        @ViewBuilder content: () -> Content
    ) {
        self.destination = destination
        self.action = action
        self.content = content()
    }

    var body: some View {
        Button(action: buttonAction, label: { content })
            .background(
                NavigationLink(
                    destination: destination,
                    isActive: $continueToDestination,
                    label: { EmptyView() }
                )
            )
    }

    private func buttonAction() {
        let token = NavigationToken {
            self.continueToDestination = true
        }

        action(token)
    }
}

struct ActionNavigationLink_Previews: PreviewProvider {
    static var previews: some View {
        NavigationView {
            VStack(spacing: 32) {
                // This behaves exactly as a `NavigationLink` would
                ActionNavigationLink(
                    destination: EmptyView(),
                    action: { $0.navigate() }
                ) {
                    Text("Immediate")
                }

                // This adds a 3 second delay, simulating an API call, then navigates
                ActionNavigationLink(
                    destination: EmptyView(),
                    action: { token in
                        DispatchQueue.main.asyncAfter(deadline: .now() + .seconds(3)) {
                            token.navigate()
                        }
                    }
                ) {
                    Text("Delayed")
                }
            }
            .navigationBarTitle("Examples")
        }
    }
}