SwiftUI: Forcing an Update

Question

Normally, we're restricted from discussing Apple prerelease stuff, but I've already seen plenty of SwiftUI discussions, so I suspect that it's OK; just this once.

I am in the process of driving into the weeds on one of the tutorials (I do that).

I am adding a pair of buttons below the swipeable screens in the "Interfacing With UIKit" tutorial: https://developer.apple.com/tutorials/swiftui/interfacing-with-uikit

These are "Next" and "Prev" buttons. When at one end or the other, the corresponding button hides. I have that working fine.

The problem that I'm having, is accessing the UIPageViewController instance represented by the PageViewController.

I have the currentPage property changing (by making the PageViewController a delegate of the UIPageViewController), but I need to force the UIPageViewController to change programmatically.

I know that I can "brute force" the display by redrawing the PageView body, reflecting a new currentPage, but I'm not exactly sure how to do that.

struct PageView<Page: View>: View {
    var viewControllers: [UIHostingController<Page>]
    @State var currentPage = 0

    init(_ views: [Page]) {
        self.viewControllers = views.map { UIHostingController(rootView: $0) }
    }
    
    var body: some View {
        VStack {
            PageViewController(controllers: viewControllers, currentPage: $currentPage)

            HStack(alignment: .center) {
                Spacer()
                
                if 0 < currentPage {
                    Button(action: {
                        self.prevPage()
                    }) {
                        Text("Prev")
                    }
                    
                    Spacer()
                }
                
                Text(verbatim: "Page \(currentPage)")
                
                if currentPage < viewControllers.count - 1 {
                    Spacer()
                    
                    Button(action: {
                        self.nextPage()
                    }) {
                        Text("Next")
                    }
                }

                Spacer()
            }
        }
    }

    func nextPage() {
        if currentPage < viewControllers.count - 1 {
            currentPage += 1
        }
    }
    
    func prevPage() {
        if 0 < currentPage {
            currentPage -= 1
        }
    }
}

I know the answer should be obvious, but I'm having difficulty figuring out how to programmatically refresh the VStack or body.

Answer 1

Setting currentPage, as it is a @State, will reload the whole body.