import SwiftUI
struct ContentView: View {
@State private var username = ""
@State private var isLoggedIn = false
@StateObject private var viewModel = LoginViewModel()
var body: some View {
if isLoggedIn {
HomeView(username: username)
} else {
LoginForm(
username: $username,
isLoggedIn: $isLoggedIn,
viewModel: viewModel
)
}
}
}
struct LoginForm: View {
@Binding var username: String
@Binding var isLoggedIn: Bool
@ObservedObject var viewModel: LoginViewModel
var body: some View {
VStack(spacing: 20) {
TextField("Username", text: $username)
.textFieldStyle(RoundedBorderTextFieldStyle())
.autocapitalization(.none)
SecureField("Password", text: $viewModel.password)
.textFieldStyle(RoundedBorderTextFieldStyle())
Button("Login") {
viewModel.login(username: username) { success in
isLoggedIn = success
}
}
.disabled(username.isEmpty || viewModel.password.isEmpty)
if viewModel.isLoading {
ProgressView()
}
if let error = viewModel.errorMessage {
Text(error)
.foregroundColor(.red)
.font(.caption)
}
}
.padding()
}
}
import Foundation
import Combine
class LoginViewModel: ObservableObject {
@Published var password = ""
@Published var isLoading = false
@Published var errorMessage: String?
private var cancellables = Set<AnyCancellable>()
func login(username: String, completion: @escaping (Bool) -> Void) {
isLoading = true
errorMessage = nil
// Simulate API call
DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
self.isLoading = false
if username.isEmpty || self.password.isEmpty {
self.errorMessage = "Invalid credentials"
completion(false)
} else {
completion(true)
}
}
}
}
SwiftUI revolutionizes iOS development with declarative syntax where you describe what the UI should look like based on state. Views automatically update when state changes using property wrappers like @State, @Binding, and @ObservedObject. The @State wrapper creates source of truth for simple value types, while @Binding creates two-way connections to pass state down the view hierarchy. For complex state shared across views, I use ObservableObject with @Published properties. SwiftUI's runtime efficiently diffs and updates only what changed, eliminating manual UI updates. This reactive approach reduces bugs and makes UI code more predictable and testable.
