可以做到。尽管您不需要跟踪尽可能多的状态。

首先，您只需要跟踪它们是否失败。因此，您的failedRegister将跟踪用户是否已成功注册。这意味着我们可以删除successfulRegister。

我们需要一个变量来跟踪是否显示警报，为此，我们将使用变量showAlert

当您有一个提供用户信息的链接列表时，我们将仅使用包含几个用户名的数组来对此进行模拟。

这是应该工作的简化代码。

struct ContentView: View {

    var names: [String] = ["John","Mike"]

    @State var username: String = ""
    @State var password : String = ""
    @State private var failedRegister = false

    // this value is used for tracking whether the alert should be shown
    @State private var showAlert = false

    var body: some View {
        VStack {
            TextField("Enter username",text: $username)

            Button(action: {
                // reset to false as this is the initial state
                self.failedRegister = false

                if (self.names.contains(self.username)){
                    self.failedRegister.toggle()
                } else {
                    // insert the value into the user info
                }
                self.showAlert.toggle()

            }) {
                Text("Register")
                    .font(.headline)
                    .foregroundColor(.white)
                    .padding()
                    .frame(width: 220,height: 60)
                    .background(Color.green)
                    .cornerRadius(15.0)
            }

        }.alert(isPresented: $showAlert) {
            // it would be nice to set failedRegister back to false in this function but you cannot modify state here.
            if self.failedRegister {
                return  Alert(title: Text("Failed to register"),message: Text("Unfortunately that username is taken"),dismissButton: .default(Text("OK")))
            } else {
                return  Alert(title: Text("Welcome"),message: Text("You have registered"),dismissButton: .default(Text("OK")))
            }
        }
    }
}

虽然安德鲁的回答非常有用，但这里是一个“长话短说”的答案，适用于 iOS14：

struct YourView: View {
    enum AlertType: Identifiable {
        case first,second
        
        var id: Int {
            hashValue
        }
    }
    
    @State var alertType: AlertType?
    
    var body: some View {
        VStack {
            Button("Show alert #1") {
                alertType = .first
            }
            
            Button("Show alert #2") {
                alertType = .second
            }
        }
        .alert(item: $alertType) { type in
            switch type {
            case .first:
                return Alert(title: Text("First alert"))
            case .second:
                return Alert(title: Text("Second alert"))
            }
        }
    }
}

与Andrew解决方案相同，但枚举超出了ContentView的范围，该枚举允许在其他视图中使用，并在一个位置进行分组

enum Choice {
    case success
    case failure
}

extension Choice: Identifiable {
    var id: Choice { self }
}

struct ContentView:View {
    .../...
}