Creates a download task to resume a previously canceled or failed download and calls a handler upon completion.
- iOS 7.0+
- macOS 10.9+
- tvOS 9.0+
- watchOS 2.0+
A data object that provides the data necessary to resume the download.
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
Task With Resume Data:
The location of a temporary file where the server’s response is stored. You must move this file or open it for reading before your completion handler returns. Otherwise, the file is deleted, and the data is lost.
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
An error object that indicates why the request failed, or
nilif the request was successful.
The new session download task.
By using a completion handler, the task bypasses calls to delegate methods for response and data delivery, and instead provides any resulting data, response, or error 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
Your app can obtain a
resume object in two ways:
If your app cancels an existing transfer by calling
cancel, the session object passes a
By Producing Resume Data:
resumeobject to the completion handler that you provided in that call.
If a transfer fails, the session object provides an
NSErrorobject either to its delegate or to the task’s completion handler. In that object, the
NSURLSessionkey in the
Download Task Resume Data
userdictionary contains a
After you create the task, you must start it by calling its
If the request completes successfully, the
location parameter of the completion handler block contains the location of the temporary file, and the
error parameter is
nil. If the request fails, the
location 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.