Hey everyone,
I’m learning async/await and trying to fetch an image from a URL off the main thread to avoid overloading it, while updating the UI afterward. Before starting the fetch, I want to show a loading indicator (UI-related work). I’ve implemented this in two different ways using Task and Task.detached, and I have some doubts:
Is using Task { @MainActor the better approach?
I added @MainActor because, after await, the resumed execution might not return to the Task's original actor. Is this the right way to ensure UI updates are done safely?
Does calling fetchImage() on @MainActor force it to run entirely on the main thread?
I used an async data fetch function (not explicitly marked with any actor). If I were to use a completion handler instead, would the function run on the main thread?
Is using Task.detached overkill here?
I tried Task.detached to ensure the fetch runs on a non-main actor. However, it seems to involve unnecessary actor hopping since I still need to hop back to the main actor for UI updates. Is there any scenario where Task.detached would be a better fit?
class ViewController : UIViewController{
override func viewDidLoad() {
super.viewDidLoad()
//MARK: First approch
Task{@MainActor in
showLoading()
let image = try? await fetchImage() //Will the image fetch happen on main thread?
updateImageView(image:image)
hideLoading()
}
//MARK: 2nd approch
Task{@MainActor in
showLoading()
let detachedTask = Task.detached{
try await self.fetchImage()
}
updateImageView(image:try? await detachedTask.value)
hideLoading()
}
}
func fetchImage() async throws -> UIImage {
let url = URL(string: "https://via.placeholder.com/600x400.png?text=Example+Image")!
//Async data function call
let (data, response) = try await URLSession.shared.data(from: url)
guard let httpResponse = response as? HTTPURLResponse, httpResponse.statusCode == 200 else {
throw URLError(.badServerResponse)
}
guard let image = UIImage(data: data) else {
throw URLError(.cannotDecodeContentData)
}
return image
}
func showLoading(){
//Show Loader handling
}
func hideLoading(){
//Hides the loader
}
func updateImageView(image:UIImage?){
//Image view updated
}
}
