Switching view states with enums

Paul Hudson    @twostraws    December 23rd 2023

You’ve seen how we can use regular Swift conditions to present one type of view or the other, like this:

if Bool.random() {
    Rectangle()
} else {
    Circle()
}

Tip: When returning different kinds of view, make sure you’re either inside the body property or using something like @ViewBuilder or Group.

Where conditional views are particularly useful is when we want to show one of several different states, and if we plan it correctly we can keep our view code small and also easy to maintain – it’s a great way to start training your brain to think about SwiftUI architecture.

There are two parts to this solution. The first is to define an enum for the various view states you want to represent. For example, you might define this as a nested enum:

enum LoadingState {
    case loading, success, failed
}

Next, create individual views for those states. I’m just going to use simple text views here, but they could hold anything:

struct LoadingView: View {
    var body: some View {
        Text("Loading...")
    }
}

struct SuccessView: View {
    var body: some View {
        Text("Success!")
    }
}

struct FailedView: View {
    var body: some View {
        Text("Failed.")
    }
}

Those views could be nested if you want, but they don’t have to be – it really depends on whether you plan to use them elsewhere and the size of your app.

With those two parts in place, we now effectively use ContentView as a simple wrapper that tracks the current app state and shows the relevant child view. That means giving it a property to store the current LoadingState value:

@State private var loadingState = LoadingState.loading

Then filling in its body property with code that shows the correct view based on the enum value, like this:

if loadingState == .loading {
    LoadingView()
} else if loadingState == .success {
    SuccessView()
} else if loadingState == .failed {
    FailedView()
}

You can also use a switch block instead, like this:

switch loadingState {
case .loading:
    LoadingView()
case .success:
    SuccessView()
case .failed:
    FailedView()
}

Tip: Switching over an enum has the advantage that Swift checks all our cases are covered correctly, which means if you add another case in the future you'll be told to handle it correctly.

Using this approach our ContentView doesn’t spiral out of control as more and more code gets added to the views, and in fact has no idea what loading, success, or failure even look like.

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