Handling Large JSON Responses in Swift with Codable and performance optimization
I keep running into I'm working on an iOS app using Swift 5 and the Combine framework to fetch and decode a large JSON response from a REST API. The JSON data is around 5MB and consists of a complex nested structure. When I try to decode it using `JSONDecoder` with `Codable`, I experience important delays, and the app becomes unresponsive, especially on older devices. Here’s the code snippet I’m using to make the network call and decode the JSON: ```swift import Combine struct User: Codable { let id: Int let name: String let posts: [Post] } struct Post: Codable { let id: Int let title: String let body: String } class ViewModel: ObservableObject { @Published var users: [User] = [] private var cancellables = Set<AnyCancellable>() func fetchUsers() { guard let url = URL(string: "https://api.example.com/users") else { return } URLSession.shared.dataTaskPublisher(for: url) .map { $0.data } .decode(type: [User].self, decoder: JSONDecoder()) .receive(on: DispatchQueue.main) .sink(receiveCompletion: { completion in switch completion { case .finished: break case .failure(let behavior): print("behavior fetching users: \(behavior)") } }, receiveValue: { [weak self] users in self?.users = users }) .store(in: &cancellables) } } ``` While this approach works, I'm getting the following warning in the console after the decoding process: ``` Warning: Thread 1: Fatal behavior: Unexpectedly found nil while unwrapping an Optional value ``` I suspect it might be due to the size of the data and possibly running out of memory or a timing scenario with updating the UI. I've tried running this code on both the iOS Simulator and physical devices, and the performance is still sluggish. I've considered using a background thread for the decoding process, but I’m not sure how to implement that with Combine effectively. Additionally, would there be any best practices for optimizing the decoding of large JSON responses, such as using streaming or pagination? Any insights or suggestions would be greatly appreciated! Am I missing something obvious?