Simple Login form to demonstrate change of focus in SwiftUI

login.swift

struct Login: View {
    @State private var username = ""
    @State private var password = ""
    enum Field: Hashable {
        case username
        case password
    }
    @FocusState private var focusedField: Field?
    
    var body: some View {
        Form {
            TextField("Username", text: $username)
                .focused($focusedField, equals: .username)
            
            SecureField("Password", text: $password)
                .focused($focusedField, equals: .password)
            
            Button("Sign In") {
                if username.isEmpty {
                    focusedField = .username
                } else if password.isEmpty {
                    focusedField = .password
                } else {
                    self.focusedField = nil
                    // handle login
                }
            }
        }
    }
}