SwiftUI - Animate transition

Question

I have a sign out button on a modal sheet that takes the user back to the login screen. To accomplish this I first dismiss the sheet and then, using asyncAfter(deadline:) I set an environment variable that causes the login page to appear. Everything works fine, but once the sheet is dismissed, the transition from the view under the sheet to the login page is pretty jarring. Mostly because there isn't one. The top view just disappears, revealing the login view. I know I can create custom transitions, but I can't figure out where to attach it. Say, for example, I want to fade out the view underneath the sheet. (Although, I'm open to any kind of transition!)

This is the struct that directs the traffic:

struct ConductorView: View {
   @EnvironmentObject var tower: Tower
   let onboardingCompleted = UserDefaults.standard.bool(forKey: "FirstVisit")
    
   var body: some View {
      VStack {
         if tower.currentPage == .onboarding {
            Onboarding1View()
         } else if tower.currentPage == .login {
            LoginView()
         } else if tower.currentPage == .idle {
            LoginView()
         }
      }.onAppear{
         if self.onboardingCompleted {
            self.tower.currentPage = .login
         } else {
            self.tower.currentPage = .onboarding
         }
      }
   }
}

And this is the sign out button on the sheet:

Button(action: {
   self.presentationMode.wrappedValue.dismiss()
   DispatchQueue.main.asyncAfter(deadline: .now() + 0.3) {
      self.tower.currentPage = .login
   }
}) {
   Text("Sign Out")
}

Martijn Pieters · Accepted Answer · 2022-08-23 14:36:39Z

Here is a simplified demo on your replicated code (and I made some longer delay to make it mode visible). Of course you will need to tune it for your needs by changing type of transition or animation, etc. Tested with Xcode 12 / iOS 14

class Tower: ObservableObject {
    enum PageType {
        case onboarding, login, idle
    }
    @Published var currentPage: PageType = .onboarding
}

struct ConductorView: View {
   @EnvironmentObject var tower: Tower
   let onboardingCompleted = false

   var body: some View {
      VStack {
         if tower.currentPage == .onboarding {
            Onboarding1View()
         } else if tower.currentPage == .login {
            Text("LoginView")
                .transition(.move(edge: .trailing))    // << here !!
         } else if tower.currentPage == .idle {
            Text("IdleView")
         }
      }
      .animation(.default, value: tower.currentPage)   // << here !!
      .onAppear{
         if self.onboardingCompleted {
            self.tower.currentPage = .login
         } else {
            self.tower.currentPage = .onboarding
         }
      }
   }
}


struct Onboarding1View: View {
   @EnvironmentObject var tower: Tower
    @Environment(\.presentationMode) var presentationMode
    @State private var isPresented = true
    var body: some View {
        Text("Login")
            .sheet(isPresented: $isPresented) {
                Button(action: {
                   self.presentationMode.wrappedValue.dismiss()
                   DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
                      self.tower.currentPage = .login
                   }
                }) {
                   Text("Sign Out")
                }
            }
    }
}

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