# URLProtocol An abstract class that handles the loading of protocol-specific URL data. ``` class URLProtocol ``` ## Overview Don’t instantiate a [`URLProtocol`](/documentation/Foundation/URLProtocol) subclass directly. Instead, create subclasses for any custom protocols or URL schemes that your app supports. When a download starts, the system creates the appropriate protocol object to handle the corresponding URL request. You define your protocol class and call the [`registerClass(_:)`](/documentation/Foundation/URLProtocol/registerClass(_:)) class method during your app’s launch time so that the system is aware of your protocol. > Note: > You cannot use this class to define custom URL schemes and protocols in watchOS 2 and later. To support the customization of protocol-specific requests, create extensions to the [`URLRequest`](/documentation/Foundation/URLRequest) class to provide any custom API that you need. You can store and retrieve protocol-specific request data by using [`URLProtocol`](/documentation/Foundation/URLProtocol)’s class methods [`property(forKey:in:)`](/documentation/Foundation/URLProtocol/property(forKey:in:)) and [`setProperty(_:forKey:in:)`](/documentation/Foundation/URLProtocol/setProperty(_:forKey:in:)). Create a [`URLResponse`](/documentation/Foundation/URLResponse) for each request your subclass processes successfully. You may want to create a custom [`URLResponse`](/documentation/Foundation/URLResponse) class to provide protocol specific information. ### Subclassing notes When overriding methods of this class, be aware that methods that take a `task` parameter are preferred by the system to those that do not. Therefore, you should override the task-based methods when subclassing, as follows: Swift: - Initialization — Override [`init(task:cachedResponse:client:)`](/documentation/Foundation/URLProtocol/init(task:cachedResponse:client:)) instead of or in addition to [`init(request:cachedResponse:client:)`](/documentation/Foundation/URLProtocol/init(request:cachedResponse:client:)). Also override the task-based [`canInit(with:)`](/documentation/Foundation/URLProtocol/canInit(with:)-18gbo) instead of or in addition to the request-based [`canInit(with:)`](/documentation/Foundation/URLProtocol/canInit(with:)-76brg). Objective-C: - Initialization — Override [`canInit(with:)`](/documentation/Foundation/URLProtocol/canInit(with:)-18gbo) and [`init(task:cachedResponse:client:)`](/documentation/Foundation/URLProtocol/init(task:cachedResponse:client:)) instead of or in addition to [`canInit(with:)`](/documentation/Foundation/URLProtocol/canInit(with:)-76brg) and [`init(request:cachedResponse:client:)`](/documentation/Foundation/URLProtocol/init(request:cachedResponse:client:)). ## Topics ### Creating protocol objects [`init(request:cachedResponse:client:)`](/documentation/Foundation/URLProtocol/init(request:cachedResponse:client:)) Creates a URL protocol instance to handle the request. [`init(task:cachedResponse:client:)`](/documentation/Foundation/URLProtocol/init(task:cachedResponse:client:)) Creates a URL protocol instance to handle the task. ### Registering and unregistering protocol classes [`registerClass(_:)`](/documentation/Foundation/URLProtocol/registerClass(_:)) Attempts to register a subclass of [`URLProtocol`](/documentation/Foundation/URLProtocol), making it visible to the URL loading system. [`unregisterClass(_:)`](/documentation/Foundation/URLProtocol/unregisterClass(_:)) Unregisters the specified subclass of [`URLProtocol`](/documentation/Foundation/URLProtocol). ### Determining If a subclass can handle a request [`canInit(with:)`](/documentation/Foundation/URLProtocol/canInit(with:)-76brg) Determines whether the protocol subclass can handle the specified request. [`canInit(with:)`](/documentation/Foundation/URLProtocol/canInit(with:)-18gbo) Determines whether the protocol subclass can handle the specified task. ### Getting and setting request properties [`property(forKey:in:)`](/documentation/Foundation/URLProtocol/property(forKey:in:)) Fetches the property associated with the specified key in the specified request. [`setProperty(_:forKey:in:)`](/documentation/Foundation/URLProtocol/setProperty(_:forKey:in:)) Sets the property associated with the specified key in the specified request. [`removeProperty(forKey:in:)`](/documentation/Foundation/URLProtocol/removeProperty(forKey:in:)) Removes the property associated with the specified key in the specified request. ### Providing a canonical version of a request [`canonicalRequest(for:)`](/documentation/Foundation/URLProtocol/canonicalRequest(for:)) Returns a canonical version of the specified request. ### Determining if requests are cache equivalent [`requestIsCacheEquivalent(_:to:)`](/documentation/Foundation/URLProtocol/requestIsCacheEquivalent(_:to:)) A Boolean value indicating whether two requests are equivalent for cache purposes. ### Starting and stopping downloads [`startLoading()`](/documentation/Foundation/URLProtocol/startLoading()) Starts protocol-specific loading of the request. [`stopLoading()`](/documentation/Foundation/URLProtocol/stopLoading()) Stops protocol-specific loading of the request. ### Getting protocol attributes [`cachedResponse`](/documentation/Foundation/URLProtocol/cachedResponse) The protocol’s cached response. [`client`](/documentation/Foundation/URLProtocol/client) The object the protocol uses to communicate with the URL loading system. [`URLProtocolClient`](/documentation/Foundation/URLProtocolClient) The interface used by [`URLProtocol`](/documentation/Foundation/URLProtocol) subclasses to communicate with the URL Loading System. [`request`](/documentation/Foundation/URLProtocol/request) The protocol’s request. [`task`](/documentation/Foundation/URLProtocol/task) The protocol’s task. --- 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)