tag(_:includeOptional:)

Declaration

nonisolated func tag<V>(_ tag: V, includeOptional: Bool = true) -> some View where V : Hashable

Parameters

• tag:

  A Hashable value to use as the view’s tag.

• includeOptional:

  If the tag value for Optional<V> should also be set.

Return Value

A view with the specified tag set.

Discussion

Use this modifier to differentiate among certain selectable views, like the possible values of a Picker or the tabs of a TabView. Tag values can be of any type that conforms to the Hashable protocol.

This modifier will write the tag value for the type V, as well as Optional<V> if includeOptional is enabled. Containers checking for tags of either type will see the value as set.

In the example below, the ForEach loop in the Picker view builder iterates over the Flavor enumeration. It extracts the string value of each enumeration element for use in constructing the row label, and uses the enumeration value as input to the tag(_:) modifier.

struct FlavorPicker: View {
    enum Flavor: String, CaseIterable, Identifiable {
        case chocolate, vanilla, strawberry
        var id: Self { self }
    }

    @State private var selectedFlavor: Flavor? = nil

    var body: some View {
        Picker("Flavor", selection: $selectedFlavor) {
            ForEach(Flavor.allCases) { flavor in
                Text(flavor.rawValue)
                    .tag(flavor)
            }
        }
    }
}

The selection type of the Picker is an Optional<Flavor> and so it will look for tags on its contents of Optional<Flavor> type. Since the tag modifier defaults to having includeOptional enabled, even though the tag for each option is a non-optional Flavor, the tag modifier writes values for both the non-optional, and optional versions of the value, allowing the contents to be selectable by the Picker.

A ForEach automatically applies a default tag to each enumerated view using the id parameter of the corresponding element. If the element’s id parameter and the picker’s selection input have exactly the same type, or the same type but optional, you can omit the explicit tag modifier.

To see examples that don’t require an explicit tag, see Picker.

See Also

Managing the view hierarchy

• id(_:)
• equatable()