SwiftUI doesn't like switch?

Question

Trying to following this discussion, I implemented the suggestion of Yurii Kotov:

struct ContentView: View {

@State private var index = 0

@ViewBuilder
 var body: some View {
   if index == 0 {
       MainView()
   } else {
       LoginView()
   }
}

It works fine. But if I try to use a switch statement instead:

    switch  index {
        case 0: MainView()
        case 1: LoginView()
        default:
            print("# error in switch")
        }

nothing happens. There is no mistake alert, but also no result at all. Could somebody help?

Your switch statement does not do the same thing as the if. If you write an equivalent switch statement, then it should work. — Sweeper, Jan 22 '20 at 07:21
Think about the case when `index` is 2. What will the if do? What will the switch do? — Sweeper, Jan 22 '20 at 07:23
It s an interesting discussion, but I have defined index as 0, so it should be not interesting for switch what happens by 1000. It should match the 0 case. IMHO. — Roman, Jan 22 '20 at 07:26
Whenever a `@State` changes, your view updates, which means that everything in `body` is evaluated again. — Sweeper, Jan 22 '20 at 07:29
My mistake, I didn't think your code would compile in the first place... — Sweeper, Jan 22 '20 at 07:42
As said, I got the positive result, using the if-statement. But what to do, if you have more cases and more views in play? — Roman, Jan 22 '20 at 07:46
After reading the other answers in your linked post. It appears that the `ViewBuilder` function builder turns if statements into `_ConditionalContent`s, which is strictly a "either this or that" thing. You would have to nest if statements to achieve more cases. But if your true intention is to have more cases, you better use `AnyView`. See Mike Glukhov's answer. — Sweeper, Jan 22 '20 at 07:58

score 8 · Answer 1 · answered Oct 25 '20 at 14:23

I had an issue with the default case where I wanted a "break" type situation for the switch to be exhaustive. SwiftUI requires some type of view, I found that

EmptyView() solved the issue.

also noted here EmptyView Discussion that you "have to return something"

struct FigureListMenuItems: View {
    var showContextType: ShowContextEnum
    @Binding var isFavoriteSeries: Bool?

    var body: some View {
    
        Menu {
            switch showContextType {
            case .series:
                Button(action: { toggleFavoriteSeries() }) {
                    isFavoriteSeries! ?
                    Label("Favorite Series?", systemImage: "star.fill")
                        .foregroundColor(.yellow)
                    :
                    Label("Favorite Series?", systemImage: "star")
                        .foregroundColor(.yellow)
                }
            default: // <-- can use EmptyView() in this default too if you want
                Button(action: {}) {
                    Text("No menu items")
                }
            }
        } label: {
            switch showContextType {
            case .series:
                isFavoriteSeries! ?
                Image(systemName: "star.fill")
                    .foregroundColor(.yellow)
                :
                Image(systemName: "star")
                    .foregroundColor(.yellow)
            default:
                EmptyView()
            }
            Label("Menu", systemImage: "ellipsis.circle")
        }
    }

    private func toggleFavoriteSeries() {
        isFavoriteSeries?.toggle()
    }
}

Enum for switch

enum ShowContextEnum: Int {
    case series = 1
    case whatIsNew = 2
    case allFigures = 3
}

Hrabovskyi Oleksandr · Accepted Answer · 2020-01-22T09:45:23.520

As @Sweeper said: your if...else and switch...case statements are not equal. The main idea is: body is just a computed variable of a View protocol and it should return something of its' type. Sure, you can do it with switch...case statements. In your code snippet mistake is in default statement: body cannot return() -> Void, only some View. So your code should looks like this:

struct ViewWithSwitchStatements: View {

    @State var option = 0

    var body: some View {

        switch option {
        case 1:
            return AnyView(Text("Option 1"))
        case 2:
            return AnyView(Text("Option 2"))
        default:
            return AnyView(Text("Wrong option!"))
        }

    }
}

However you can't put it into VStack or something else, like if...else statements.

Also, be careful and avoid returning Opaque types from ViewBuilders (don't wrap in AnyView) as it hides all the type information and compiler cannot optimise so well. — kdeo, Dec 22 '21 at 20:39

SwiftUI doesn't like switch?

2 Answers2