Use enum to indicate state in SwiftUI

Login.swift

//
//  ContentView.swift
//  Test5
//

//import SwiftUI
//
//struct ContentView: View {
//    var body: some View {
//        Text("Hello, world!")
//            .padding()
//    }
//}

import SwiftUI
import Combine

struct ContentView: View {

    init() {
        UITableView.appearance().backgroundColor = .clear
    }

    enum UserStatus {
        case valid, invalid, unknown
    }

    // Form Variables

    @FocusState private var isFocused: Bool

    @State private var username = ""
    @State private var status: UserStatus = .unknown

    let namesInUse = Set([
        "foobar23",
        "blah1234",
    ])

//    func validUsername() -> String {
//        if (username.count < 8) {
//            return ""
//        }
//        return namesInUse.contains(username.lowercased()) ? "❌" : "✅"
//    }

    func validateUsername() {
        if username.count < 8 {
            status = .unknown
            return
        }

        if namesInUse.contains(username.lowercased()) {
            status = .invalid
            return
        }

        // username is good to go
        status = .valid
    }

    @ViewBuilder
    func ValidUsername() -> some View {
        switch status {
            case .unknown:
                EmptyView()
            case .valid:
                Image(systemName: "checkmark.circle")
                    .foregroundColor(Color.green)
            case .invalid:
                Image(systemName: "x.square")
                    .foregroundColor(Color.red)
        }
    }

    var body: some View {
        VStack(spacing: 20) {
            Text("Username")
            TextField("", text: $username)
                .multilineTextAlignment(.center)
                .textCase(.lowercase)
                .autocapitalization(.none)
                .focused($isFocused)
                .keyboardType(.default)
                .onReceive(Just(username)) { newValue in
                    let filtered = newValue.filter { "abcdefghijklmnopqrstuvwxyz0123456789".contains($0) }
                    if filtered != newValue {
                        self.username = filtered
                    }
                    validateUsername()
                } // End of onReceive

                .submitLabel(.done)
                .border(Color.blue)
            ValidUsername()
                .font(.largeTitle)

            if status == .valid {
                Button("Continue") {
                    print("continue pressed")
                }
                .buttonStyle(.bordered)
            }
            Spacer()

        }
//        List {
//            Group {
//
//                Section {
//
//                    HStack {
//                        Text("Username")
//                        ZStack(alignment: .trailing) {
//                            if username.isEmpty {
//                                Text("johnsmith")
//                                    .foregroundColor(Color("GrayText"))
//                            }
//                            TextField("", text: $username)
//                                .multilineTextAlignment(.trailing)
//                                .textCase(.lowercase)
//                                .autocapitalization(.none)
//                                .focused($isFocused)
//                                .keyboardType(.default)
//                                .onReceive(Just(username)) { newValue in
//                                    let filtered = newValue.filter { "abcdefghijklmnopqrstuvwxyz0123456789".contains($0) }
//                                    if filtered != newValue {
//                                        self.username = filtered
//                                    }
//                                } // End of onReceive
//
//                                .submitLabel(.done)
//                            ValidUsername()
//                            //Text("\(validUsername())")
//
//                        } // End of ZStack
//
//                    } // End of HStack
//
//                } // End Section
//
//            } // End Group
//            .listRowBackground(Color("FieldBkg"))
//            .listRowSeparatorTint(Color("sepLine"))
//            .listRowSeparator(.visible)
//
//        } // End List
//        .listStyle(GroupedListStyle())
//        .foregroundColor(Color("WhiteText"))
//        .accentColor(Color("WhiteText"))

    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}