SwiftUI Property Wrappers Deep Dive: @State'den @Observable'a

1// @State kullandığında aslında olan:
2@State private var count = 0
3 
4// Derleyici bunu şuna çevirir:
5private var _count = State<Int>(initialValue: 0)
6var count: Int {
7    get { _count.wrappedValue }
8    nonmutating set { _count.wrappedValue = newValue }
9}
10 
11// $ prefix ile projectedValue'ya erişirsin:
12// $count → Binding<Int>

1struct CounterView: View {
2    // ✅ View-local state - sadece bu view yönetir
3    @State private var count = 0
4    @State private var isAnimating = false
5 
6    var body: some View {
7        VStack(spacing: 20) {
8            Text("\(count)")
9                .font(.largeTitle)
10                .scaleEffect(isAnimating ? 1.2 : 1.0)
11 
12            Button("Artır") {
13                count += 1
14                withAnimation(.spring()) {
15                    isAnimating = true
16                }
17                DispatchQueue.main.asyncAfter(deadline: .now() + 0.3) {
18                    withAnimation { isAnimating = false }
19                }
20            }
21        }
22    }
23}

1// Parent - state'in sahibi
2struct ParentView: View {
3    @State private var isOn = false
4 
5    var body: some View {
6        // $isOn → Binding<Bool> oluşturur
7        ToggleRow(title: "Bildirimler", isOn: $isOn)
8    }
9}
10 
11// Child - state'e referans
12struct ToggleRow: View {
13    let title: String
14    @Binding var isOn: Bool  // Parent'ın state'ine referans
15 
16    var body: some View {
17        Toggle(title, isOn: $isOn)
18    }
19}
20 
21// ✅ Custom Binding oluşturma
22struct SettingsView: View {
23    @State private var volume: Double = 0.5
24 
25    var body: some View {
26        Slider(value: Binding(
27            get: { volume },
28            set: { newValue in
29                volume = min(max(newValue, 0), 1) // Clamp 0-1
30                HapticManager.impact(.light) // Side effect
31            }
32        ))
33    }
34}

1class UserViewModel: ObservableObject {
2    @Published var name = ""
3    @Published var email = ""
4    @Published var isLoading = false
5 
6    func loadProfile() async {
7        isLoading = true
8        defer { isLoading = false }
9        // API çağrısı...
10    }
11}
12 
13// ✅ DOĞRU: İlk oluşturan view'da @StateObject
14struct ProfileScreen: View {
15    @StateObject private var viewModel = UserViewModel()
16 
17    var body: some View {
18        VStack {
19            ProfileHeader(viewModel: viewModel) // Aşağı geçir
20            ProfileForm(viewModel: viewModel)
21        }
22        .task { await viewModel.loadProfile() }
23    }
24}
25 
26// ✅ DOĞRU: Alt view'da @ObservedObject
27struct ProfileHeader: View {
28    @ObservedObject var viewModel: UserViewModel
29 
30    var body: some View {
31        Text(viewModel.name).font(.title)
32    }
33}
34 
35// ❌ YANLIŞ: Alt view'da @StateObject - her rebuild'de yeni instance!
36struct BrokenProfileHeader: View {
37    @StateObject var viewModel = UserViewModel() // HER REBUILD'DE YENİ!
38    var body: some View { Text(viewModel.name) }
39}

1class AppState: ObservableObject {
2    @Published var currentUser: User?
3    @Published var isAuthenticated = false
4    @Published var theme: AppTheme = .system
5}
6 
7// Root'ta inject et
8@main
9struct MyApp: App {
10    @StateObject private var appState = AppState()
11 
12    var body: some Scene {
13        WindowGroup {
14            ContentView()
15                .environmentObject(appState) // Tüm alt view'lar erişebilir
16        }
17    }
18}
19 
20// Herhangi bir alt view'da kullan
21struct SettingsView: View {
22    @EnvironmentObject var appState: AppState
23 
24    var body: some View {
25        Form {
26            Text("Merhaba, \(appState.currentUser?.name ?? "Misafir")")
27            Toggle("Dark Mode", isOn: Binding(
28                get: { appState.theme == .dark },
29                set: { appState.theme = $0 ? .dark : .light }
30            ))
31        }
32    }
33}

1struct AdaptiveView: View {
2    @Environment(\.colorScheme) var colorScheme
3    @Environment(\.dynamicTypeSize) var typeSize
4    @Environment(\.dismiss) var dismiss
5    @Environment(\.horizontalSizeClass) var sizeClass
6 
7    var body: some View {
8        VStack {
9            Text("Tema: \(colorScheme == .dark ? "Karanlık" : "Aydınlık")")
10 
11            if sizeClass == .regular {
12                // iPad veya büyük ekran
13                HStack { content }
14            } else {
15                // iPhone
16                VStack { content }
17            }
18 
19            Button("Kapat") { dismiss() }
20        }
21    }
22 
23    @ViewBuilder var content: some View {
24        Text("İçerik 1")
25        Text("İçerik 2")
26    }
27}
28 
29// Custom EnvironmentKey oluşturma
30struct AnalyticsKey: EnvironmentKey {
31    static let defaultValue: AnalyticsService = DefaultAnalyticsService()
32}
33 
34extension EnvironmentValues {
35    var analytics: AnalyticsService {
36        get { self[AnalyticsKey.self] }
37        set { self[AnalyticsKey.self] = newValue }
38    }
39}
40 
41// Kullanım
42struct TrackableView: View {
43    @Environment(\.analytics) var analytics
44 
45    var body: some View {
46        Button("Satın Al") {
47            analytics.track("purchase_tapped")
48        }
49    }
50}

1struct SettingsView: View {
2    // UserDefaults'a otomatik persist edilir
3    @AppStorage("username") var username = "Misafir"
4    @AppStorage("notifications_enabled") var notificationsEnabled = true
5    @AppStorage("app_theme") var appTheme = "system"
6 
7    // Scene-level storage (tab, window bazlı)
8    @SceneStorage("selected_tab") var selectedTab = 0
9    @SceneStorage("scroll_position") var scrollPosition: String?
10 
11    var body: some View {
12        Form {
13            TextField("Kullanıcı adı", text: $username)
14            Toggle("Bildirimler", isOn: $notificationsEnabled)
15            Picker("Tema", selection: $appTheme) {
16                Text("Sistem").tag("system")
17                Text("Aydınlık").tag("light")
18                Text("Karanlık").tag("dark")
19            }
20        }
21    }
22}

1// ✅ iOS 17+ Modern yaklaşım
2@Observable
3class UserStore {
4    var name = ""
5    var email = ""
6    var isLoading = false
7    var posts: [Post] = []
8 
9    func loadPosts() async {
10        isLoading = true
11        defer { isLoading = false }
12        posts = try? await PostService.fetchAll() ?? []
13    }
14}
15 
16// View'da kullanım - @StateObject/@ObservedObject YOK!
17struct ProfileView: View {
18    @State private var store = UserStore() // Sadece @State yeterli!
19 
20    var body: some View {
21        // SwiftUI otomatik olarak sadece kullanılan property'leri takip eder
22        // name değişince BU view rebuild olur
23        // email değişince bu view ETKİLENMEZ (kullanılmıyor çünkü)
24        VStack {
25            Text(store.name).font(.title)
26 
27            if store.isLoading {
28                ProgressView()
29            } else {
30                PostList(posts: store.posts)
31            }
32        }
33        .task { await store.loadPosts() }
34    }
35}
36 
37// Alt view'a geçirme - @ObservedObject YOK!
38struct PostList: View {
39    let posts: [Post]  // Sadece let!
40 
41    var body: some View {
42        ForEach(posts) { post in
43            Text(post.title)
44        }
45    }
46}