制作符合 SwiftUI 协议的结构列表

Question

我有一个自定义协议说

protocol CustomProtocol {}

我有一个自定义结构 say

struct CustomStruct: View, CustomProtocol

如何使 (CustomStruct, CustomStruct) 符合 CustomProtocol

我有一个自定义 ViewBuilder，它有一个初始化函数，

init<views>(@ViewBuilder content: @escaping () -> TupleView<Views>)

现在我只想接受符合 CustomProtocol 的视图

示例：

struct CustomStruct: View {
var views: [AnyView]

init<Views: CustomProtocol>(@ViewBuilder content: @escaping () -> TupleView<Views>) {
    self.views = content().getViews
}

我为 getViews 变量添加了元组视图的扩展：

extension TupleView {
var getViews: [AnyView] {
    makeArray(from: value)
}

private struct GenericView {
    let body: Any
    
    var anyView: AnyView? {
        AnyView(_fromValue: body)
    }
}

private func makeArray<Tuple>(from tuple: Tuple) -> [AnyView] {
    func convert(child: Mirror.Child) -> AnyView? {
        withUnsafeBytes(of: child.value) { ptr -> AnyView? in
            let binded = ptr.bindMemory(to: GenericView.self)
            return binded.first?.anyView
        }
    }
    
    let tupleMirror = Mirror(reflecting: tuple)
    return tupleMirror.children.compactMap(convert)
}

}

Answer 1

我能想到的唯一方法就是重新发明你自己的ViewBuilder:

@resultBuilder
struct MyCustomViewBuilder {
    static func buildBlock<C0, C1>(_ c0: C0, _ c1: C1) -> TupleView<(C0, C1)> where C0 : View & CustomProtocol, C1 : View & CustomProtocol {
        ViewBuilder.buildBlock(c0, c1)
    }
    static func buildBlock<C0, C1, C2>(_ c0: C0, _ c1: C1, _ c2: C2) -> TupleView<(C0, C1, C2)> where C0 : View & CustomProtocol, C1 : View & CustomProtocol, C2: View & CustomProtocol {
        ViewBuilder.buildBlock(c0, c1, c2)
    }

    // and so on...
}

ViewBuilder 有最多 10 个视图的 buildBlock 重载（这就是为什么你不能在 ViewBuilder 中放置超过 10 个视图的原因），所以你可以写如果你也想的话，可以重载 10 次。不幸的是，无法使用可变参数，因为 View 具有关联类型:(

然后你可以这样做例如：

struct CustomStack<Views>: View {
    var body: some View {
        content
    }
    
    let views: [AnyView]
    let content: TupleView<Views>

    // note the change from @ViewBuilder to @CustomViewBuilder
    init(@MyCustomViewBuilder content: @escaping () -> TupleView<Views>) {
        let view = content()
        self.views = view.getViews
        self.content = view
    }
}

现在如果你这样做：

CustomStack {
    Text("Hello")
    Text("World")
}

编译器会抱怨Text不符合CustomProtocol。

制作符合 SwiftUI 协议的结构列表

Make a list of Structs conform to a protocol SwiftUI

swift

swift-protocols

swiftui