preparePreviewOfFile(at:completionHandler:)
Prepares the preview of a file at the specified file’s URL.
Declaration
optional func preparePreviewOfFile(at url: URL, completionHandler handler: @escaping @Sendable ((any Error)?) -> Void)optional func preparePreviewOfFile(at url: URL) async throwsParameters
- url:
The URL of the file to preview.
- handler:
A completion handler that notifies the platform that a preview is available. The operating system shows a loading spinner, so call the handler as soon as possible. You can call the completion handler asynchronously after returning from the callback.
Discussion
The operating system calls this method only once from the main thread before it presents the previewing controller. To avoid blocking the main thread, don’t perform long-running or resource-intensive work.
When preparing and displaying the view controller, avoid holding open a file descriptors while the user is previewing the file.