# coordinate(readingItemAt:options:writingItemAt:options:error:byAccessor:) Initiates a read operation that contains a follow-up write operation. ``` func coordinate(readingItemAt readingURL: URL, options readingOptions: NSFileCoordinator.ReadingOptions = [], writingItemAt writingURL: URL, options writingOptions: NSFileCoordinator.WritingOptions = [], error outError: NSErrorPointer, byAccessor readerWriter: (URL, URL) -> Void) ``` ## Parameters `readingURL` A URL identifying the file or directory to read. If other objects or processes are acting on the item at the URL, the actual URL passed to the block in the `readerWriter` parameter may be different than the one in this parameter. `readingOptions` One of the reading options described in [`NSFileCoordinator.ReadingOptions`](/documentation/Foundation/NSFileCoordinator/ReadingOptions). If you pass `0` for this parameter, the [`savePresentedItemChanges(completionHandler:)`](/documentation/Foundation/NSFilePresenter/savePresentedItemChanges(completionHandler:)) method of relevant file presenters is called before your block executes. `writingURL` A URL identifying the file or directory to write. If other objects or processes are acting on the item at the URL, the actual URL passed to the block in the `readerWriter` parameter may be different than the one in this parameter. `writingOptions` One of the writing options described in [`NSFileCoordinator.WritingOptions`](/documentation/Foundation/NSFileCoordinator/WritingOptions). The options you specify partially determine how file presenters are notified and how this file coordinator object waits to execute your block. `outError` On input, a pointer to a pointer for an error object. If a file presenter encounters an error while preparing for this operation, that error is returned in this parameter and the block in the `readerWriter` parameter is not executed. If you cancel this operation before the `readerWriter` block is executed, this parameter contains an error object on output. `readerWriter` A [Block object](https://developer.apple.com/library/archive/documentation/General/Conceptual/DevPedia-CocoaCore/Block.html#//apple_ref/doc/uid/TP40008195-CH3) containing the read and write operations you want to perform in a coordinated manner. This block receives [`NSURL`](/documentation/Foundation/NSURL) objects containing the URLs of the items to read and write and returns no value. Always use the URLs passed into the block instead of the values in the `readingURL` and `writingURL` parameters. ## Discussion When invoking these methods, declare a `__block` variable before the accessor block and initialize it to a value that signals failure, and then inside the accessor block set it to a value that indicates success. If the coordinated operation fails, then the accessor block never runs. The sentinel variable still holds a value that indicates failure, and the [`NSError`](/documentation/Foundation/NSError) out parameter contains a reference that describes the error. You use this method to perform a read operation that might also contain a write operation that needs to be coordinated. This method executes synchronously, blocking the current thread until the `readerWriter` block finishes executing. When performing the write operation, you may call the [`coordinate(writingItemAt:options:error:byAccessor:)`](/documentation/Foundation/NSFileCoordinator/coordinate(writingItemAt:options:error:byAccessor:)) method from your `readerWriter` block. This method does the canonical lock ordering that is required to prevent a potential deadlock of the file operations. This method makes the same calls to file presenters, and has the same general wait behavior, as the [`coordinate(readingItemAt:options:error:byAccessor:)`](/documentation/Foundation/NSFileCoordinator/coordinate(readingItemAt:options:error:byAccessor:)) method. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)