Child view init called everytime tab changes

[csbence10]

Hi!

I'm experimenting with TCA and I'd like to create a page tab view. My code is:

struct TabState: Equatable {
    enum TabName: String {
        case monday
        case tuesday
        case wednesday
        case thursday
        case friday
        case saturday
        case sunday
    }

    var selectedTab: TabName
}

enum TabAction: Equatable {
    case tabSelected(TabState.TabName)
}

let tabReducer = Reducer<TabState, TabAction, Void> { state, action, _ in
    switch action {
    case .tabSelected(let tab):
        state.selectedTab = tab
        return .none
    }
}

struct RandomView: View {
    let name: TabState.TabName

    init(name: TabState.TabName) {
        self.name = name
        print("\(name) init called")
    }
    var body: some View {
        Text("\(name.rawValue)")
    }
}

struct TabViewDemo: View {
    let store: Store<TabState, TabAction>
    var body: some View {
        WithViewStore(self.store) { viewStore in
            TabView(selection: viewStore.binding(get: \.selectedTab, send: TabAction.tabSelected)) {
                RandomView(name: .monday).tag(TabState.TabName.monday)
                RandomView(name: .tuesday).tag(TabState.TabName.tuesday)
                RandomView(name: .wednesday).tag(TabState.TabName.wednesday)
                RandomView(name: .thursday).tag(TabState.TabName.thursday)
                RandomView(name: .friday).tag(TabState.TabName.friday)
                RandomView(name: .saturday).tag(TabState.TabName.saturday)
                RandomView(name: .sunday).tag(TabState.TabName.sunday)
            }
                .tabViewStyle(PageTabViewStyle())
        }
    }
}

So this way when I start the app it prints:

monday init called
tuesday init called
wednesday init called
thursday init called
friday init called
saturday init called
sunday init called

and if I swipe to change tab, on every tab change all of the RandomViews initialized again so for example my console contains 3 times 7 prints after 2 tab changes.

However, if I change the TabViewDemo view to this:

struct TabViewDemo: View {
    @State var selectedTab: TabState.TabName = .monday
    var body: some View {
            TabView(selection: $selectedTab) {
                RandomView(name: .monday).tag(TabState.TabName.monday)
                RandomView(name: .tuesday).tag(TabState.TabName.tuesday)
                RandomView(name: .wednesday).tag(TabState.TabName.wednesday)
                RandomView(name: .thursday).tag(TabState.TabName.thursday)
                RandomView(name: .friday).tag(TabState.TabName.friday)
                RandomView(name: .saturday).tag(TabState.TabName.saturday)
                RandomView(name: .sunday).tag(TabState.TabName.sunday)
            }
                .tabViewStyle(PageTabViewStyle())
    }
}

it prints the same thing ONCE and no more on tab changes.

Am I missing something? Or is this a bug? Any ideas?

[mbrandonw]

Hey @csbence10, thanks for the discussion and I was able to reproduce this too. It's very strange. There must be some kind of special SwiftUI magic when using @State bindings in TabView that prevents the additional inits. If you convert the @State to @ObservedObject you will see that the inits are called gain. So definitely seems like a SwiftUI bug 😬.

FWIW, you should't fret too much about the .init calls. Since you should never do series work in the initializer of a view those calls are usually not a problem. It's the calls to the body that can be expensive (with sufficiently complex view hierarchies), and the WithViewStore is preventing those from being invoked too many times.