👀 Views: 423 💬 Answers: 1 📅 Created: 2025-06-12

swift swiftui state

I'm performance testing and I'm working on a SwiftUI app where I have a `State` variable that is supposed to update and reflect changes in the UI when the view appears. However, I'm experiencing a delay in the UI update that seems to occur only under certain conditions. Specifically, I have a view that fetches data using an API call in the `onAppear` modifier, and I noticed that, even though the data is fetched correctly, the UI does not update immediately when the `@State` variable changes. Here is a basic example of my setup: ```swift struct ContentView: View { @State private var items: [String] = [] var body: some View { List(items, id: \.self) { item in Text(item) } .onAppear { fetchData() } } private func fetchData() { DispatchQueue.global().async { // Simulating network delay Thread.sleep(forTimeInterval: 2) let fetchedItems = ["Item 1", "Item 2", "Item 3"] DispatchQueue.main.async { self.items = fetchedItems } } } } ``` In this example, I expect the list to populate two seconds after the view appears. However, there's a noticeable delay before the UI is updated, and sometimes it appears as if the list is empty until the fetch completes. I've tried wrapping the `fetchData` call in `DispatchQueue.main.async` but that didn't seem to change anything. Additionally, when I inspect the `items` array in the debugger, it appears to have the correct items immediately after the API fetch, but the UI does not reflect these changes until I interact with the view (e.g., scrolling or tapping). I’m also using iOS 17 and SwiftUI 3.0. Any suggestions on how to ensure the UI updates as expected without these delays? What's the best practice here?