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01-GettingStarted-OptionalState.swift
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01-GettingStarted-OptionalState.swift
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import ComposableArchitecture
import SwiftUI
private let readMe = """
This screen demonstrates how to show and hide views based on the presence of some optional child \
state.
The parent state holds a `Counter.State?` value. When it is `nil` we will default to a plain \
text view. But when it is non-`nil` we will show a view fragment for a counter that operates on \
the non-optional counter state.
Tapping "Toggle counter state" will flip between the `nil` and non-`nil` counter states.
"""
@Reducer
struct OptionalBasics {
@ObservableState
struct State: Equatable {
var optionalCounter: Counter.State?
}
enum Action {
case optionalCounter(Counter.Action)
case toggleCounterButtonTapped
}
var body: some Reducer<State, Action> {
Reduce { state, action in
switch action {
case .toggleCounterButtonTapped:
state.optionalCounter =
state.optionalCounter == nil
? Counter.State()
: nil
return .none
case .optionalCounter:
return .none
}
}
.ifLet(\.optionalCounter, action: \.optionalCounter) {
Counter()
}
}
}
struct OptionalBasicsView: View {
let store: StoreOf<OptionalBasics>
var body: some View {
Form {
Section {
AboutView(readMe: readMe)
}
Button("Toggle counter state") {
store.send(.toggleCounterButtonTapped)
}
if let store = store.scope(state: \.optionalCounter, action: \.optionalCounter) {
Text(template: "`Counter.State` is non-`nil`")
CounterView(store: store)
.buttonStyle(.borderless)
.frame(maxWidth: .infinity)
} else {
Text(template: "`Counter.State` is `nil`")
}
}
.navigationTitle("Optional state")
}
}
#Preview {
NavigationStack {
OptionalBasicsView(
store: Store(initialState: OptionalBasics.State()) {
OptionalBasics()
}
)
}
}
#Preview("Deep-linked") {
NavigationStack {
OptionalBasicsView(
store: Store(
initialState: OptionalBasics.State(
optionalCounter: Counter.State(
count: 42
)
)
) {
OptionalBasics()
}
)
}
}