Is there a way in SwiftUI to transport and handle data from an property to the class?

Question

I have two classes here. Music which is used to store music url and load metadata, and MusicManager which is used to store a list of music and sort them after loading of all music's metadata finished.

Since the loading of metadata for each music let metadata = try? await asset.load(.commonMetadata) is asynchronous, I can't directly call sort function in init().

I tried to find some solution using Publisher in Combine framework that when the metadata is loaded, the publisher will emit a completion, and if MusicManager received enough completion (same as music list's count), it will perform the sort.

class Music: ObservableObject, Identifiable {
    static let publisher = PassthroughSubject<Void,Error>
......
}

class MusicManager: ObservableObject {
......
    static var count = 0
    let subscriber = Music.pub.sink { completion in
        switch completion {
        case .finished:
            count += 1
            if musicList.count == count {
                ......
            }
        case .failure(_):
        }
    } receiveValue: { _ in }
......
}

But it said Instance member 'library' cannot be used on type 'MusicListManager'; did you mean to use a value of this type instead?

How can I am informed, when all music's metadata are already loaded. I would appreciate it if you can give me some advice.

Answer 1

We don't normally use sink with ObservableObject, instead we assign the end of the Combine pipeline to an @Published which also makes the lifetime of the pipeline the same as the object's, so there is no need to store cancellables.

However, you mentioned you are using async/await. If using that you don't need ObservableObject anymore. Just pass the asset into your View as a let param, and then use the task modifier to call your async/await code and set an @State with the result which will cause body to be called. SwiftUI will calculate the View hierarchy diff and update the UIKit/AppKit views on screen with the changes.