# contents(forType:) Returns the document data to be saved. ``` func contents(forType typeName: String) throws -> Any ``` ## Parameters `typeName` The file type of the document, a Uniform Type Identifier (UTI). This string typically derives from the [`fileType`](/documentation/UIKit/UIDocument/fileType) property. If you want to save the document under a different UTI, you can override the [`savingFileType`](/documentation/UIKit/UIDocument/savingFileType) method. ## Return Value The document data to be saved, or `nil` if you cannot return document data. The returned object is typically an instance of the class for flat files or the class for file packages. If you return `nil`, you should also return an error object in `outError`. If you return an object other than an or object, you must override the [`writeContents(_:andAttributes:safelyTo:for:)`](/documentation/UIKit/UIDocument/writeContents(_:andAttributes:safelyTo:for:)) or [`writeContents(_:to:for:originalContentsURL:)`](/documentation/UIKit/UIDocument/writeContents(_:to:for:originalContentsURL:)) method to handle the writing of data. ## Discussion When you subclass [`UIDocument`](/documentation/UIKit/UIDocument), override this method to provide UIKit with the document data for saving. This method is called on the queue that the [`save(to:for:completionHandler:)`](/documentation/UIKit/UIDocument/save(to:for:completionHandler:)) method was called on (typically, the main queue). Writing of data occurs on a background queue. The default implementation of this method returns `nil`. When you return a non-`nil` value in the `outError` parameter, the completion handlers for the following methods don’t get called: - [`save(to:for:completionHandler:)`](/documentation/UIKit/UIDocument/save(to:for:completionHandler:)) - [`autosave(completionHandler:)`](/documentation/UIKit/UIDocument/autosave(completionHandler:)) - [`close(completionHandler:)`](/documentation/UIKit/UIDocument/close(completionHandler:)) Instead, in this case, the error is available to your app in the [`handleError(_:userInteractionPermitted:)`](/documentation/UIKit/UIDocument/handleError(_:userInteractionPermitted:)) method and in the [`stateChangedNotification`](/documentation/UIKit/UIDocument/stateChangedNotification) notification. If you want more control over the saving operation than this method provides—for example, if you want to perform incremental writing of data — override, instead, one of the lower-level data-writing methods such as [`writeContents(_:andAttributes:safelyTo:for:)`](/documentation/UIKit/UIDocument/writeContents(_:andAttributes:safelyTo:for:)) or [`writeContents(_:to:for:originalContentsURL:)`](/documentation/UIKit/UIDocument/writeContents(_:to:for:originalContentsURL:)). These methods are called on a background thread. > Handling Errors in Swift: > In Swift, this method is marked with the `throws` keyword to indicate that it throws an error in cases of failure. > > When overriding this method, use the `throw` statement to throw an `NSError`, as described in [Error Handling](https://docs.swift.org/swift-book/LanguageGuide/ErrorHandling.html) in [The Swift Programming Language](https://docs.swift.org/swift-book/) and `About Imported Cocoa Error Parameters`. ## See Also [`open(completionHandler:)`](/documentation/UIKit/UIDocument/open(completionHandler:)) Opens a document asynchronously. [`revert(toContentsOf:completionHandler:)`](/documentation/UIKit/UIDocument/revert(toContentsOf:completionHandler:)) Reverts a document to the most recent document data stored on-disk. --- 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)