Alternative to switch statement in SwiftUI ViewBuilder block?

Question

⚠️ 23 June 2020 Edit: From Xcode 12, both switch and if let statements will be supported in the ViewBuilder!

I’ve been trying to replicate an app of mine using SwiftUI. It has a RootViewController which, depending on an enum value, shows a different child view controller. As in SwiftUI we use views instead of view controllers, my code looks like this:

struct RootView : View {    @State var containedView: ContainedView = .home     var body: some View {       // custom header goes here       switch containedView {          case .home: HomeView()          case .categories: CategoriesView()          ...       }    } } 

Unfortunately, I get a warning:

Closure containing control flow statement cannot be used with function builder ViewBuilder.

So, are there any alternatives to switch so I can replicate this behaviour?

Answer 1

⚠️ 23 June 2020 Edit: From Xcode 12, both switch and if let statements will be supported in the ViewBuilder!

Thanks for the answers, guys. I’ve found a solution on Apple’s Dev Forums. It’s answered by Kiel Gillard. The solution is to extract the switch in a function as Lu_, Linus and Mo suggested, but we have to wrap the views in AnyView for it to work – like this:

struct RootView: View {   @State var containedViewType: ContainedViewType = .home    var body: some View {      VStack {        // custom header goes here        containedView()      }   }    func containedView() -> AnyView {      switch containedViewType {      case .home: return AnyView(HomeView())      case .categories: return AnyView(CategoriesView())      ...    } } 

Answer 2

Update: SwiftUI 2 now includes support for switch statements in function builders, https://github.com/apple/swift/pull/30174

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Adding to Nikolai's answer, which got the switch compiling but not working with transitions, here's a version of his example that does support transitions.

struct RootView: View {   @State var containedViewType: ContainedViewType = .home    var body: some View {      VStack {        // custom header goes here        containedView()      }   }    func containedView() -> some View {      switch containedViewType {      case .home: return AnyView(HomeView()).id("HomeView")      case .categories: return AnyView(CategoriesView()).id("CategoriesView")      ...    } } 

Note the id(...) that has been added to each AnyView. This allows SwiftUI to identify the view within it's view hierarchy allowing it to apply the transition animations correctly.