import SwiftUI
struct PostDetailView: View {
@StateObject private var viewModel: PostDetailViewModel
init(postId: Int) {
_viewModel = StateObject(wrappedValue: PostDetailViewModel(postId: postId))
}
var body: some View {
ScrollView {
VStack(alignment: .leading, spacing: 16) {
if viewModel.isLoading {
ProgressView()
} else if let post = viewModel.post {
Text(post.title)
.font(.title)
.fontWeight(.bold)
HStack {
Image(systemName: "person.circle")
Text(post.author.name)
.font(.subheadline)
Spacer()
Text(post.createdAt, style: .date)
.font(.caption)
.foregroundColor(.secondary)
}
Divider()
Text(post.body)
.font(.body)
HStack(spacing: 20) {
Button(action: viewModel.toggleLike) {
Label("\(viewModel.likesCount)", systemImage: viewModel.isLiked ? "heart.fill" : "heart")
}
.foregroundColor(viewModel.isLiked ? .red : .primary)
Label("\(post.commentsCount)", systemImage: "bubble.left")
}
.padding(.top)
CommentsSection(comments: viewModel.comments)
} else if let error = viewModel.errorMessage {
Text(error)
.foregroundColor(.red)
}
}
.padding()
}
.navigationTitle("Post")
.onAppear {
viewModel.loadPost()
}
}
}
import Foundation
import Combine
class PostDetailViewModel: ObservableObject {
@Published var post: Post?
@Published var comments: [Comment] = []
@Published var isLoading = false
@Published var errorMessage: String?
@Published var isLiked = false
@Published var likesCount = 0
private let postId: Int
private let networkService: NetworkService
private var cancellables = Set<AnyCancellable>()
init(postId: Int, networkService: NetworkService = .shared) {
self.postId = postId
self.networkService = networkService
}
func loadPost() {
isLoading = true
errorMessage = nil
Publishers.Zip(
networkService.fetchPost(id: postId),
networkService.fetchComments(postId: postId)
)
.sink(
receiveCompletion: { [weak self] completion in
self?.isLoading = false
if case .failure(let error) = completion {
self?.errorMessage = error.localizedDescription
}
},
receiveValue: { [weak self] post, comments in
self?.post = post
self?.comments = comments
self?.isLiked = post.likedByCurrentUser
self?.likesCount = post.likesCount
}
)
.store(in: &cancellables)
}
func toggleLike() {
guard let post = post else { return }
// Optimistic update
isLiked.toggle()
likesCount += isLiked ? 1 : -1
networkService.toggleLike(postId: post.id)
.sink(
receiveCompletion: { [weak self] completion in
if case .failure = completion {
// Rollback on error
self?.isLiked.toggle()
self?.likesCount += (self?.isLiked ?? false) ? -1 : 1
}
},
receiveValue: { _ in }
)
.store(in: &cancellables)
}
}
MVVM (Model-View-ViewModel) separates concerns cleanly in iOS apps. Models hold data, Views display UI, and ViewModels mediate between them with business logic and state. Views bind to ViewModel properties using Combine or SwiftUI's property wrappers. ViewModels expose @Published properties that Views observe. This separation makes code testable—ViewModels can be unit tested without UI, and Views become thin presentation layers. I keep ViewModels framework-agnostic, importing only Foundation, not UIKit or SwiftUI. Navigation and coordination logic goes in Coordinators. This architecture scales well from small to large apps while maintaining clear boundaries.
