Opening FileDocument with URL → should only be called in the main thread

Question

Created May ’25

Replies 4

Boosts 0

Participants 2

Its document says openDocument can open a document at a specific URL. So I've saved a model as a JSON object with its URL and a bookmark as Data. With its security-scoped bookmark data resolved, I am able to open a document except that the app will crash right after opening a document. Console says

should only be called in the main thread

 struct ContentView: View {
    @EnvironmentObject var bookmarkViewModel: BookmarkViewModel
    
    var body: some View {
		VStack {
		
		}
		.onAppear {
			loadBookmarks()
		}
}
 
extension ContentView {
    func loadBookmarks() {        
        print("1 \(Thread.current)") // NSMainThread
        
        Task {
            for bookmarkItem in bookmarkViewModel.bookmarkItems { // resolving a security-scoped bookmark
                print("2 \(Thread.current)") // NSMainThread
                if let _ = resolveBookmark(bookmarkData: bookmarkItem.bookmarkData) {
                    print("3 \(Thread.current)") // NSMainThread                    
                    do {
                        print("4 \(Thread.current)") // NSMainThread                        
                        try await openDocument(at: bookmarkItem.bookmarkURL)                        
                        print("5 \(Thread.current)") // NSMainThread                        
                    } catch {
                        print("\(error.localizedDescription)")
                    }
                }
            }
        }
    }
}

Well, the application is on the main thread. I've checked every line before and after opening a document with its URL. Call what on the main thread? This is confusing. Thanks.

 class BookmarkViewModel: ObservableObject {
    @Published var bookmarkItems: [BookmarkItem] = []
    
    var defaultFileManager: FileManager {
        return FileManager.default
    }
    
    var documentURL: URL? {
        ...
    }
    
    init() {
        fetchBookmarkItems()
    }
    
    func fetchBookmarkItems() {
        bookmarkItems.removeAll()
        
        if let documentURL {
            let bookmarkFolderURL = documentURL.appending(path: "MyApp").appending(path: "Bookmarks")
            do {
                let contents = try defaultFileManager.contentsOfDirectory(atPath: bookmarkFolderURL.path)
                for content in contents {
                    ...
                	let fileURL = bookmarkFolderURL.appending(path: content)
                    let data = try Data(contentsOf: fileURL)
                    let bookmarkItem = try JSONDecoder().decode(BookmarkItem.self, from: data)
                    bookmarkItems.append(bookmarkItem)
                }
            } catch {
                print("Error fetching folder content: \(error.localizedDescription)")
            }
        }
    }
}

 struct BookmarkItem: Codable, Hashable {
    let bookmarkURL: URL
    let date: Date
    let bookmarkData: Data
    let open: Bool
}

Boost

Answer 1

jaimez OP

May ’25

Try using the .task view modifier and removing the Task {} from the function instead.

0

Answer 2

Tomato OP

May ’25

Okay. I get it. If I look at openDocument, it's labeled

@Environment @MainActor

That's where the main thread issue comes to surface, I guess.

0

Answer 3

Tomato OP

May ’25

Try using the .task view modifier and removing the Task {} from the function instead.

Thanks. But that's not really the main issue here.

0

Answer 4

Tomato OP

May ’25

Accepted Answer

I've upgraded my system to macOS 15.5. The bug has been system.

0

	struct ContentView: View {
	@EnvironmentObject var bookmarkViewModel: BookmarkViewModel

	var body: some View {
	VStack {

	}
	.onAppear {
	loadBookmarks()
	}
	}

	extension ContentView {
	func loadBookmarks() {
	print("1 \(Thread.current)") // NSMainThread

	Task {
	for bookmarkItem in bookmarkViewModel.bookmarkItems { // resolving a security-scoped bookmark
	print("2 \(Thread.current)") // NSMainThread
	if let _ = resolveBookmark(bookmarkData: bookmarkItem.bookmarkData) {
	print("3 \(Thread.current)") // NSMainThread
	do {
	print("4 \(Thread.current)") // NSMainThread
	try await openDocument(at: bookmarkItem.bookmarkURL)
	print("5 \(Thread.current)") // NSMainThread
	} catch {
	print("\(error.localizedDescription)")
	}
	}
	}
	}
	}
	}

	class BookmarkViewModel: ObservableObject {
	@Published var bookmarkItems: [BookmarkItem] = []

	var defaultFileManager: FileManager {
	return FileManager.default
	}

	var documentURL: URL? {
	...
	}

	init() {
	fetchBookmarkItems()
	}

	func fetchBookmarkItems() {
	bookmarkItems.removeAll()

	if let documentURL {
	let bookmarkFolderURL = documentURL.appending(path: "MyApp").appending(path: "Bookmarks")
	do {
	let contents = try defaultFileManager.contentsOfDirectory(atPath: bookmarkFolderURL.path)
	for content in contents {
	...
	let fileURL = bookmarkFolderURL.appending(path: content)
	let data = try Data(contentsOf: fileURL)
	let bookmarkItem = try JSONDecoder().decode(BookmarkItem.self, from: data)
	bookmarkItems.append(bookmarkItem)
	}
	} catch {
	print("Error fetching folder content: \(error.localizedDescription)")
	}
	}
	}
	}

	struct BookmarkItem: Codable, Hashable {
	let bookmarkURL: URL
	let date: Date
	let bookmarkData: Data
	let open: Bool
	}