Uveďte property wrapper, ktorý deklaruje sémantiku…

@State
@Binding
@EnvironmentObject
@ObservedObject
@StateObject

Tieto property wrapper-i ne deklarirat semantika na referencata vo tradicionalno razbiranje (kao pokazatel vo C++), no dozvoljavaat rabota so podatoci, predstaveni vo SwiftUI kato "referenci" ili obsht mutable iztochnici na istina. Tiy upravlyavat jivotniya cikŭl na podatocite i osiguravat avtomatichno obnovyavane na UI pri tyahnata promena.

Primeri:

@State: Upravlyava lokalnoto sostoyanie vnutre v View. Promyanata na @State promenliva vodi do prekarasvane na View.

struct MyView: View {
    @State private var isActive = false

    var body: some View {
        Button("Toggle") {
            isActive.toggle()
        }
    }
}

@Binding: Pozvoljava suzdavane na dvuposochna svŭrzka kum @State ili drug iztochnik na podatoci. Promenite na edno myasto se otrazqvat na drugoto.

struct ParentView: View {
    @State private var value = 0

    var body: some View {
        VStack {
            Text("Value: \(value)")
            ChildView(count: $value) // $ suzdava Binding
        }
    }
}

struct ChildView: View {
    @Binding var count: Int // Poluchava Binding

    var body: some View {
        Button("Increment") {
            count += 1 // Promyana na Binding
        }
    }
}

@ObservedObject: Izpolzva se za referentni tipove (klasove), koito implementirat protokola ObservableObject. Promyanata na @Published svojstvata v tozi obekt vodi do obnovyavane na View.

import Combine

class Counter: ObservableObject {
    @Published var count = 0
}

struct ContentView: View {
    @ObservedObject var counter = Counter() // Referenten tip

    var body: some View {
        VStack {
            Text("Count: \(counter.count)")
            Button("Increment") {
                counter.count += 1
            }
        }
    }
}

@StateObject: Podobno na @ObservedObject, no prednaznachen za suzdavane na instanciq ObservableObject vnutre v View i upravlenie na jivotniya mu cikŭl. View stava sobstvenik na obekta.

import Combine

class TimerData: ObservableObject {
    @Published var timerSeconds = 0

    init() {
        Timer.scheduledTimer(withTimeInterval: 1, repeats: true) { _ in
            self.timerSeconds += 1
        }
    }
}

struct TimerView: View {
    @StateObject var timerData = TimerData() // Suzdavane i sobstvenost na obekta

    var body: some View {
        Text("Time: \(timerData.timerSeconds)")
    }
}

@EnvironmentObject: Pozvoljava da se passvat instancii ObservableObject v hierarhiyata na View, bez da se passvat chrez konstruktorite na vseki View.

import Combine

class UserSettings: ObservableObject {
    @Published var loggedIn = false
}

struct AppView: View {
    @StateObject var settings = UserSettings()

    var body: some View {
        ContentView()
            .environmentObject(settings) // Vkarvane v okolenieto
    }
}

struct ContentView: View {
    @EnvironmentObject var settings: UserSettings // Dostŭp ot okolenieto

    var body: some View {
        Toggle("Logged In", isOn: $settings.loggedIn)
    }
}

Uveďte property wrapper, ktorý deklaruje sémantiku odkazu.