SwiftUI遍历协议数组报错：要求Content遵循AccessibilityRotorContent

尝试遍历协议类型数组，让每个元素渲染对应视图。协议包含返回any View的buildView()方法，但调用时触发如下错误：

Static method 'buildExpression' requires that 'Content' conform to 'AccessibilityRotorContent'

相关代码 #

import UIKit
import SwiftUI
import PlaygroundSupport

protocol ViewItem: AnyObject, Hashable, Identifiable {
    var id: UUID { get }
    func buildView() -> any View
}

class ViewOne: ViewItem {
 
    let id: UUID = UUID()
    
    func buildView() -> any View {
        Text("View one")
    }
    
    static func == (lhs: ViewOne, rhs: ViewOne) -> Bool {
        lhs.id == rhs.id
    }
    
    func hash(into hasher: inout Hasher) {
        hasher.combine(id)
    }
    
}

class ViewTwo: ViewItem {
    
    let id: UUID = UUID()
    
    func buildView() -> any View {
        Text("View two")
    }
    
    static func == (lhs: ViewTwo, rhs: ViewTwo) -> Bool {
        lhs.id == rhs.id
    }
    
    func hash(into hasher: inout Hasher) {
        hasher.combine(id)
    }
    
}

struct ContentView: View {
    
    let viewItems: [any ViewItem]
    
    var body: some View {
        VStack {
            ForEach(viewItems, id: \.id) { viewItem in
                viewItem.buildView() <------------------ ERROR HERE
            }
        }
    }
}

解决方案 #

错误根源是SwiftUI的视图DSL无法直接处理any View这种存在类型，需要将其转换为具体的View类型（比如AnyView）。有两种修改方式：

方式一：修改协议返回类型为AnyView

直接把协议的buildView()方法返回值改为AnyView，实现类中用AnyView包裹视图：

protocol ViewItem: AnyObject, Hashable, Identifiable {
    var id: UUID { get }
    func buildView() -> AnyView
}

class ViewOne: ViewItem {
    // ... 其他代码不变
    func buildView() -> AnyView {
        AnyView(Text("View one"))
    }
}

class ViewTwo: ViewItem {
    // ... 其他代码不变
    func buildView() -> AnyView {
        AnyView(Text("View two"))
    }
}

// ContentView中无需修改，直接调用即可
struct ContentView: View {
    let viewItems: [any ViewItem]
    
    var body: some View {
        VStack {
            ForEach(viewItems, id: \.id) { viewItem in
                viewItem.buildView()
            }
        }
    }
}

方式二：调用时用AnyView包裹返回值

如果不想修改协议，在ContentView的ForEach中，将any View转换为AnyView：

struct ContentView: View {
    let viewItems: [any ViewItem]
    
    var body: some View {
        VStack {
            ForEach(viewItems, id: \.id) { viewItem in
                AnyView(viewItem.buildView())
            }
        }
    }
}

两种方式本质都是通过AnyView完成类型擦除，让SwiftUI能识别并渲染视图。

内容的提问来源于stack exchange，提问作者Mr.P