SwiftUI初始化ExternalView报错：any TogleableItem无法遵循协议

你遇到的Type 'any TogleableItem' cannot conform to 'TogleableItem'错误，核心原因是Swift泛型要求绑定具体类型，而any TogleableItem是存在类型（existential type）——它不是一个遵循TogleableItem的具体类型，而是一个能容纳所有遵循该协议类型的容器。原ExternalView的泛型约束<T: TogleableItem>要求传入单一具体类型的数组，但你传入的是混合多类型的[any TogleableItem]，泛型系统无法匹配到符合要求的具体类型，因此报错。

下面提供两种可行的解决方案：

方案一：直接适配存在类型 #

修改ExternalView放弃泛型，直接处理[any TogleableItem]数组（any TogleableItem继承自Hashable，可满足InternalView的约束）：

修改后的ExternalView #

public struct ExternalView: View {
    private let items: [any TogleableItem]
    private let onItemTap: (Bool, Int, any TogleableItem) -> Void
    
    public init(
        items: [any TogleableItem],
        onItemTap: @escaping (Bool, Int, any TogleableItem) -> Void
    ) {
        self.items = items
        self.onItemTap = onItemTap
    }
    
    public var body: some View {
        InternalView(
            items: items
        ) { index, element in
            Text(element.text)
                .foregroundColor(element.isSelected ? .red : .blue)
                .onTapGesture {
                    // 存在类型无法直接修改内部属性，需创建可变副本后回调替换
                    var mutableItem = element
                    mutableItem.isSelected.toggle()
                    onItemTap(mutableItem.isSelected, index, mutableItem)
                }
        }
    }
}

修改后的ContentView #

由于存在类型的不可变性，需替换数组元素而非直接修改属性：

struct ContentView: View {
    @State private var items: [any TogleableItem] = [
        FirstObject(),
        SecondObject()
    ]
    
    var body: some View {
        ExternalView(items: items) { _, index, updatedItem in
            items[index] = updatedItem
        }
    }
}

方案二：类型擦除（泛型兼容方案） #

如果需要保留原泛型设计，可创建类型擦除结构体，将不同协议实现统一包装为单一具体类型：

定义类型擦除结构体 #

struct AnyTogleableItem: TogleableItem {
    private let _text: () -> String
    private var _isSelected: () -> Bool
    private let _setIsSelected: (Bool) -> Void
    private let _hash: (inout Hasher) -> Void
    private let _isEqual: (Any) -> Bool
    
    init<T: TogleableItem>(_ item: T) {
        _text = { item.text }
        _isSelected = { item.isSelected }
        _setIsSelected = { item.isSelected = $0 }
        _hash = { hasher in item.hash(into: &hasher) }
        _isEqual = { other in
            guard let otherItem = other as? T else { return false }
            return item == otherItem
        }
    }
    
    var text: String { _text() }
    var isSelected: Bool {
        get { _isSelected() }
        set { _setIsSelected(newValue) }
    }
    
    func hash(into hasher: inout Hasher) {
        _hash(&hasher)
    }
    
    static func == (lhs: AnyTogleableItem, rhs: AnyTogleableItem) -> Bool {
        lhs._isEqual(rhs)
    }
}

修改后的ContentView #

将数组类型改为[AnyTogleableItem]，适配原ExternalView的泛型约束：

struct ContentView: View {
    @State private var items: [AnyTogleableItem] = [
        AnyTogleableItem(FirstObject()),
        AnyTogleableItem(SecondObject())
    ]
    
    var body: some View {
        ExternalView(items: items) { isSelected, index, _ in
            items[index].isSelected = isSelected
        }
    }
}

内容的提问来源于stack exchange，提问作者MarkDev