更新结构时SwiftUI导航不起作用

Question

我有一个结构列表。轻按按钮将调用结构上的变异函数，然后进行导航。

但是导航不会触发。如果删除了对变异函数self.logins[index].updateLastLogin()的调用，它将重新开始工作。为什么？

要进行复制，请将以下内容粘贴到一个空的SwiftUI项目中：

struct Login: Identifiable, Hashable {
    let id = UUID()
    let name: String
    var lastLogin: Date?

    mutating func updateLastLogin() {
        self.lastLogin = Date()
    }
}

struct ContentView: View {
    @State private var logins = ["Zaphod", "Arthur", "Ford", "Marvin", "Trillian"].map { Login(name: $0) }
    @State private var selection: Login?

    var body: some View {
        NavigationView {
            List {
                ForEach(self.logins) { login in
                    VStack {
                        NavigationLink(destination: Text(login.name).font(.largeTitle),
                                       tag: login,
                                       selection: self.$selection) {
                            EmptyView()
                        }
                        Button(action: {
                            self.navigate(login: login)
                        }, label: {
                            Text(login.name)
                        })
                    }
                }
            }
        }
    }

    func navigate(login: Login) {
        guard let index = self.logins.firstIndex(of: login) else {
            fatalError()
        }

        self.logins[index].updateLastLogin() // remove this line
        self.selection = login
    }
}

Answer 1

这里是工作方法的演示。经过Xcode 12 / iOS 14的测试

struct DemoView: View {
    @State private var logins = ["Zaphod", "Arthur", "Ford", "Marvin", "Trillian"].map { Login(name: $0) }
    @State private var selection: UUID?

    var body: some View {
        NavigationView {
            List {
                ForEach(self.logins) { login in
                    VStack {
                        NavigationLink(destination: Text(login.name).font(.largeTitle),
                                       tag: login.id,
                                       selection: self.$selection) {
                            EmptyView()
                        }
                        Button(action: {
                            self.navigate(login: login)
                        }, label: {
                            Text(login.name)
                        })
                    }
                }
            }
        }
    }

    func navigate(login: Login) {
        guard let index = self.logins.firstIndex(of: login) else {
            fatalError()
        }

        self.logins[index].updateLastLogin() // remove this line
        self.selection = login.id
    }
}