结构的通用类型 - SwiftUI

Question

我正在尝试将结构作为泛型类型（在模型中看到）传递。 我尝试使用 AnyView 来表示我的结构，但是编译器在构建时出错：

Could not cast value of type 'EagleNation_macOS.NewsView' (0x10d7ff898) to 'SwiftUI.AnyView' (0x7fff82e27670).
2021-03-17 12:35:45.932135-0500 EagleNation-macOS[24102:2436828] Could not cast value of type 'EagleNation_macOS.NewsView' (0x10d7ff898) to 'SwiftUI.AnyView' (0x7fff82e27670).
Could not cast value of type 'EagleNation_macOS.NewsView' (0x10d7ff898) to 'SwiftUI.AnyView' (0x7fff82e27670).

我用什么类型来表示 SwiftUI 中的泛型结构？

Model：

import Foundation

struct MainBackend<Destination> {
    let navDirs = [
        NavDir(title: "News", dest: NewsView() as! Destination),
        NavDir(title: "Bulletin", dest: BulletinView() as! Destination),
        NavDir(title: "Clubs", dest: ClubsView() as! Destination),
    ]
    
    struct NavDir: Identifiable {
        let title: String
        let dest: Destination
        var id = UUID()
    }
}

视图模型：

import SwiftUI

class MainCommunication {
    private var backend = MainBackend<AnyView>()
    
    // MARK: - Access to Model
    var navDirs: [MainBackend<AnyView>.NavDir] {
        backend.navDirs
    }
}

看法：

import SwiftUI

struct MainView: View {
    var body: some View {
        NavigationView {
            NavBar { NavDir in
                NavDir.dest
            }
            NewsView()
        }
    }
}

struct NavBar<Destination: View>: View {
    let navDirs = MainCommunication().navDirs
    let buildDestination: (MainBackend<AnyView>.NavDir) -> Destination
    
    var body: some View {
        VStack() {
            List(navDirs) { NavDir in
                NavigationLink(destination: buildDestination(NavDir)) {
                    Text(NavDir.title)
                }
            }
            .listStyle(SidebarListStyle())
        }
    }
}

Answer 1

您将希望它们成为AnyView - 这是将类型擦除到同质数组中的唯一方法。 但是，您不能转换为AnyView - 您必须将它们包装在AnyView()中。

这意味着您实际上根本不需要泛型：

struct MainBackend {
    let navDirs = [
        NavDir(title: "News", dest: AnyView(NewsView())),
        NavDir(title: "Bulletin", dest: AnyView(BulletinView())),
        NavDir(title: "Clubs", dest: AnyView(ClubsView())),
    ]
    
    struct NavDir: Identifiable {
        let title: String
        let dest: AnyView
        var id = UUID()
    }
}

class MainCommunication {
    private var backend = MainBackend()
    
    // MARK: - Access to Model
    var navDirs: [MainBackend.NavDir] {
        backend.navDirs
    }
}

struct MainView: View {
    var body: some View {
        NavigationView {
            NavBar { NavDir in
                NavDir.dest
            }
        }
    }
}

struct NavBar<Destination: View>: View {
    let navDirs = MainCommunication().navDirs
    let buildDestination: (MainBackend.NavDir) -> Destination
    
    var body: some View {
        VStack() {
            List(navDirs) { NavDir in
                NavigationLink(destination: buildDestination(NavDir)) {
                    Text(NavDir.title)
                }
            }
            .listStyle(SidebarListStyle())
        }
    }
}

另请参阅： 如何使用 SwiftUI 获得动态视图列表