SwiftUI state and bindings | Swift

SwiftUI updates the interface when data changes. The key question is ownership: which view owns the data, and which views can read or change it?

@State

Use @State for view-owned, temporary UI state:

struct SettingsView: View {
    @State private var notificationsEnabled = true

    var body: some View {
        Toggle("Notifications", isOn: $notificationsEnabled)
    }
}

@State is for state that belongs to this view’s position in the hierarchy. It is not persistent storage.

Binding

A binding is a two-way connection to state owned elsewhere:

struct NotificationToggle: View {
    @Binding var isOn: Bool

    var body: some View {
        Toggle("Notifications", isOn: $isOn)
    }
}

The parent owns the state:

struct SettingsView: View {
    @State private var notificationsEnabled = true

    var body: some View {
        NotificationToggle(isOn: $notificationsEnabled)
    }
}

The $ creates a binding.

One source of truth

Do not duplicate the same state in multiple views. Store it in the least common ancestor that needs to coordinate it, then pass values or bindings down.

Use a plain value when the child only needs to read:

ArticleRow(article: article)

Use a binding when the child should edit:

EditTitleField(title: $draftTitle)

Keep state small

Local state should be focused: selected tab, draft text, sheet visibility, toggle value, loading indicator. Data that belongs to the app or feature should move into a model or view model.

What to carry forward

@State stores view-owned temporary state
@Binding lets a child read and write state owned elsewhere
$value creates a binding
one source of truth prevents drift
read-only children should receive values, not bindings
persistent or feature-wide data belongs outside local view state

Next, you will manage larger observable state.