Triggers the creation of a placeholder for the given URL.
The URL of a shared document.
A block that the system calls after the placeholder is created.
The completion handler takes the following parameter:
If the placeholder was successfully written to disk, this value is nil. Otherwise, it holds an NSError object describing the error.
The system calls this method when it needs a placeholder for a document that's returned by the File Provider extension, but is not stored locally. Override providePlaceholderAtURL:completionHandler: to create a placeholder for the given URL. This task can be broken into three steps: looking up the document’s file provider item, writing the placeholder, and calling the completion handler.
After writing the placeholder to disk, call the completion handler. If any errors occur, pass them to the completion handler. The system then passes the error back to the original coordinated read or write.