Custom init with @Namespace for .matchedGeometryEffect

Question

I'm trying to pass a custom View struct with a @Namespace property for a .matchedGeometryEffect to a parent View.

Since the parent will be providing the Namespace I am using a custom init.

When I use the syntax analogous to the @Binding custom initialization Xcode forces me to use the wrapper when initializing my custom View. That in turn kills my .matchedGeometryEffect.

struct MyView<Content: View>: View {
    @Binding var matched: Bool
    @Namespace var nspace
    let content: Content
    
    init(matched: Binding<Bool>,
         nspace: Namespace,
         @ViewBuilder content: @escaping () -> Content
    ) {
        self._matched = matched
        self._nspace = nspace
        self.content = content()
    }
    
    var body: some View {
        ...
    }
}

What seems to work is using var nspace: Namespace.ID instead of @Namespace var nspace and then:

struct MyView<Content: View>: View {
    @Binding var matched: Bool
    var nspace: Namespace.ID
    let content: Content
    
    init(matched: Binding<Bool>,
         nspace: Namespace.ID,
         @ViewBuilder content: @escaping () -> Content
    ) {
        self._matched = matched
        self.nspace = nspace
        self.content = content()
    }
    
    var body: some View {
        ...
    }
}

Can this cause trouble somewhere else? Is there a better way?

Namespace.ID is exactly as it should be passed, see for example this https://stackoverflow.com/a/63131527/12299030 — Asperi, Sep 04 '20 at 17:59

score 1 · Accepted Answer · answered Sep 04 '20 at 18:09

Can this cause trouble somewhere else? Is there a better way?

It is not worse/better it is the only correct way. Let see API:

The Namespace.ID is value used to identify namespace of matched effect

/// A dynamic property type that allows access to a namespace defined
/// by the persistent identity of the object containing the property
/// (e.g. a view).
@available(iOS 14.0, macOS 11.0, tvOS 14.0, watchOS 7.0, *)
@frozen @propertyWrapper public struct Namespace : DynamicProperty {

    @inlinable public init()

    public var wrappedValue: Namespace.ID { get }     // << here !!

and as it is seen

    ///   - namespace: The namespace in which defines the `id`. New
    ///     namespaces are created by adding an `@Namespace()` variable
    ///     to a ``View`` type and reading its value in the view's body
    ///     method.
    ///   - properties: The properties to copy from the source view.
    ///   - anchor: The relative location in the view used to produce
    ///     its shared position value.
    ///   - isSource: True if the view should be used as the source of
    ///     geometry for other views in the group.
    ///
    /// - Returns: A new view that defines an entry in the global
    ///   database of views synchronizing their geometry.
    ///
    @inlinable public func matchedGeometryEffect<ID>(id: ID, 
       in namespace: Namespace.ID,                             // << here !!
       properties: MatchedGeometryProperties = .frame, anchor: UnitPoint = .center, isSource: Bool = true) -> some View where ID : Hashable

Custom init with @Namespace for .matchedGeometryEffect

1 Answers1