使用 @Namespace 为 .matchedGeometryEffect 自定义初始化

Posted 2023-02-24

【中文标题】使用 @Namespace 为 .matchedGeometryEffect 自定义初始化

【英文标题】：Custom init with @Namespace for .matchedGeometryEffect

【发布时间】：2020-09-04 17:46:47

【问题描述】：

我正在尝试将带有 @Namespace 属性的自定义视图结构传递给父视图。

由于父母将提供Namespace，因此我使用自定义init。

当我使用类似于@Binding 自定义初始化的语法时，Xcode 会强制我在初始化自定义视图时使用包装器。这反过来会杀死我的.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 
        ...
    

似乎可行的是使用var nspace: Namespace.ID 而不是@Namespace var nspace 然后：

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 
        ...
    

这会在其他地方造成麻烦吗？有没有更好的办法？

【问题讨论】：

Namespace.ID 与它应该传递的完全一样，例如，参见 ***.com/a/63131527/12299030

【参考方案1】：

这会在其他地方造成麻烦吗？有没有更好的办法？

这不是更糟/更好，它是唯一正确的方法。让我们看看 API：

Namespace.ID 是用于标识匹配效果的命名空间的值

/// 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 !!

正如所见

    ///   - 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