# dataTask(with:completionHandler:) Creates a task that retrieves the contents of the specified URL, then calls a handler upon completion. ``` func dataTask(with url: URL, completionHandler: @escaping @Sendable (Data?, URLResponse?, (any Error)?) -> Void) -> URLSessionDataTask ``` ## Parameters `url` The URL to be retrieved. `completionHandler` The completion handler to call when the load request is complete. This handler is executed on the delegate queue. If you pass `nil` , only the session delegate methods are called when the task completes, making this method equivalent to the [`dataTask(with:)`](/documentation/Foundation/URLSession/dataTask(with:)-7jpys) method. This completion handler takes the following parameters: - `data`: The data returned by the server. - `response`: An object that provides response metadata, such as HTTP headers and status code. If you are making an HTTP or HTTPS request, the returned object is actually an [`HTTPURLResponse`](/documentation/Foundation/HTTPURLResponse) object. - `error`: An error object that indicates why the request failed, or `nil` if the request was successful. ## Return Value The new session data task. ## Discussion After you create the task, you must start it by calling its [`resume()`](/documentation/Foundation/URLSessionTask/resume()) method. By using the completion handler, the task bypasses calls to delegate methods for response and data delivery, and instead provides any resulting [`NSData`](/documentation/Foundation/NSData), [`URLResponse`](/documentation/Foundation/URLResponse), and [`NSError`](/documentation/Foundation/NSError) objects inside the completion handler. Delegate methods for handling authentication challenges, however, are still called. You should pass a `nil` completion handler *only* when creating tasks in sessions whose delegates include a [`urlSession(_:dataTask:didReceive:)`](/documentation/Foundation/URLSessionDataDelegate/urlSession(_:dataTask:didReceive:)) method. If the request completes successfully, the `data` parameter of the completion handler block contains the resource data, and the `error` parameter is `nil`. If the request fails, the `data` parameter is `nil` and the `error` parameter contain information about the failure. If a response from the server is received, regardless of whether the request completes successfully or fails, the `response` parameter contains that information. --- 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)