OperationKit is an abstract generic wrapper around Foundation’s Operation class. It provides a common ground for operations that either produce a result or throw an error. There are 3 abstract classes for different kinds of operations — AsyncOperation, SyncOperation and NetworkOperation — as well as 2 concrete implementations — NetworkDataOperation and NetworkDownloadOperation.
Operations have a generic ResultType and ErrorType. In case of success, the operations’s respective successHandler will be executed and the failureHandler in case of failure. By default the callbacks will be executed on the main queue, but you can specify any queue using the callbackQueue property.
Subclasses are required to provide an implementation of the main() method that calls either finish(withResult:) or finish(withError:) upon completion. Implementations must not call super and can be certain the operation is supposed to be executed (e.g. checks for cancellation are not necessary at the beginning).
The state of operations is being managed automatically by the superclass. If your operations are long-lived (e.g. network operations), it is recommended to regularly check for cancellation in order to avoid doing unnecessary work. Neither the successHandler nor the failureHandler will be executed if an operation is cancelled.
Your subclasses of NetworkOperation must provide an implementation of createTask(with:using:) that creates an URLSessionTask using the provided URLRequest and URLSession.
All NetworkOperation classes use a closure of the type (TaskResultType, HTTPURLResponse) throws -> ResultType to evaluate their result, where TaskResultType is the type of the result produced by the URLSessionTask created earlier (e.g Data) and ResultType is final result type of the operation.
NetworkDataOperation is a concrete implementation of the NetworkOperation whose usage speaks for itself:
let url = …
let operation = NetworkDataOperation(url: url, urlSession: .shared) { data, response in
return try JSONDecoder().decode(MyObject.self, from: data)
}
operation.successHandler = { myObject in
…
}
NetworkDownloadOperation is similar to NetworkDataOperation, but returns a temporary URL where the downloaded data can be found:
let url = …
let operation = NetworkDownloadOperation<URL>(url: url, urlSession: .shared) { tempURL, response in
let finalFileURL = …
try fileManager.moveItem(at: tempURL, to: finalFileURL)
return finalFileURL
}
operation.successHandler = { fileURL in
…
}
I plan to introduce more concrete operation implementations (e.g. file operations) in future, PRs are also welcome. I’m also not 100% happy with the error handling of NetworkOperation, which currently relies on NSError.
Florian Schliep
OperationKit is available under the MIT license. See the LICENSE file for more info.