SwiftUI Time Travel

A SwiftUI state store and view that allow you to scrub through an application's state.

This is a super rough prototype: it's only meant to serve as an example of what can be done using SwiftUI.

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How this works

Any view hierarchy can use time travel: in the provided todo app, ContentView adds time travel like this:

struct ContentView : View {
    var body: some View {
        TimeTravelView(initialState: TodoState()) {
            TodoListView()
        }
    }
}

Then you can use @EnvironmentObject to access the state store from views within the hierarchy.

struct MyView: View {

    @EnvironmentObject var store: Store<TodoState>

    var body: some View {
        Text("Count: \(store.state.todoItems.count)")
    }
}

To update your application's state, use the dispatch method on the store:

struct MyView: View {

    @EnvironmentObject var store: Store<MyState>

    var body: some View {
        VStack(spacing: 10) {
            Text("Count: \(store.state.todoItems.count)")
            HStack(spacing: 10) {
                Button(action: { self.store.dispatch(event: .someEventName) }) {
                    Text("Do Something")
                }
            }
        }
    }
}

For time travel to work, all state must be accessed like this. Any state that is stored outside of the single Store<StateType> will not be controlled by the time travel view. This means that local view state (using @State) should be used sparingly (if at all).

Internally, the store keeps a stack of all states that have occured – the slider controls which of those states is used as the active (current) state.