Version history

SwiftUI rebuilds views from state. The trick is choosing the right property wrapper so ownership and updates flow the way you expect.

The core property wrappers

@State and @Binding

@State is private to a view. Pass a two-way handle to a child with @Binding using the $ prefix.

struct CounterView: View {
    @State private var count = 0
    var body: some View {
        Stepper('Count: \(count)', value: $count)
        ChildView(count: $count)
    }
}

struct ChildView: View {
    @Binding var count: Int
    var body: some View {
        Button('Reset') { count = 0 }
    }
}

Observable models

For anything beyond a couple of values, use an observable reference type. The view that creates it uses @StateObject (or the newer @Observable macro), children receive it as @ObservedObject.

final class CartModel: ObservableObject {
    @Published var items: [Item] = []
}

struct CartView: View {
    @StateObject private var cart = CartModel()
    var body: some View { /* ... */ EmptyView() }
}

The one mistake to avoid

Do not use @ObservedObject to create a model inside a view. It will be recreated on every redraw and lose its state. The view that creates and owns a model uses @StateObject; everyone downstream uses @ObservedObject.