Where is dataTaskWithRequest method used? - swift

Question

public func dataTaskWithRequest(request: NSURLRequest, completionHandler: (NSData?, NSURLResponse?, NSError?) -> Void) -> NSURLSessionDataTask
I know the usage method of above.
public func dataTaskWithRequest(request: NSURLRequest) -> NSURLSessionDataTask
But what is the usage of this method? I'm confused about how it is used.All examples I see are using the first method. The method returns no data, no error to handle, nor any response? Or is that you somehow envelope this as a task and later run in a queue?

Answer 1

You use this latter method if you've specified a delegate for a custom NSURLSession. The data is not returned to the closure, but rather the session calls your delegate's didReceiveData, which you have to implement separately.
It takes more work to implement the delegate methods, though, so you generally only do that where you absolutely have to (e.g. you want to process data as it comes in rather than waiting for all of the data to come in; you need delegate methods for custom handling of redirects and challenges; you are doing background NSURLSession with download or upload tasks rather than data tasks; etc.).
For example, to issue a simple GET request, expecting JSON response, you might define your class to conform to URLSessionDelegate, URLSessionDataDelegate, and, optionally, URLSessionTaskDelegate (called NSURLSessionDelegate, NSURLSessionDataDelegate and NSURLSessionTaskDelegate, respectively, in Objective-C and Swift 2), and then do something like the following in Swift 3:
var responseData: Data?
func performRequest() {
let url = URL(string: "http://ip.jsontest.com/")!
var request = URLRequest(url: url)
request.setValue("application/json", forHTTPHeaderField: "Accept")
let configuration = URLSessionConfiguration.default
let session = URLSession(configuration: configuration, delegate: self, delegateQueue: nil)
responseData = Data()
let task = session.dataTask(with: request)
task.resume()
}
func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {
responseData!.append(data)
}
func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
guard error == nil else {
print(error!)
return
}
do {
guard let jsonObject = try JSONSerialization.jsonObject(with: responseData!) as? [String: AnyObject] else {
print("response was not JSON dictionary")
print("responseString: \(String(data: responseData!, encoding: .utf8))")
return
}
print(jsonObject)
} catch let parseError {
print("JSON Error: \(parseError)")
}
}
Or, in Swift 2:
var responseData: NSMutableData?
func performRequest() {
let url = NSURL(string: "http://ip.jsontest.com/")!
let request = NSMutableURLRequest(URL: url)
request.setValue("application/json", forHTTPHeaderField: "Accept")
let configuration = NSURLSessionConfiguration.defaultSessionConfiguration()
let session = NSURLSession(configuration: configuration, delegate: self, delegateQueue: nil)
responseData = NSMutableData()
let task = session.dataTaskWithRequest(request)
task.resume()
}
func URLSession(session: NSURLSession, dataTask: NSURLSessionDataTask, didReceiveData data: NSData) {
responseData!.appendData(data)
}
func URLSession(session: NSURLSession, task: NSURLSessionTask, didCompleteWithError error: NSError?) {
guard error == nil else {
print(error!)
return
}
do {
guard let jsonObject = try NSJSONSerialization.JSONObjectWithData(responseData!, options: []) as? [String: AnyObject] else {
print("response was not JSON dictionary")
print("responseString: \(String(data: responseData!, encoding: NSUTF8StringEncoding))")
return
}
print(jsonObject)
} catch let parseError {
print("JSON Error: \(parseError)")
}
}
Clearly, you wouldn't do this unless you needed some of the more complicated delegate methods, too, but I wanted to show a minimalist implementation (which helps us appreciate the completion handler rendition).

Answer 2

public func dataTaskWithRequest(request: NSURLRequest, completionHandler: (NSData?, NSURLResponse?, NSError?) -> Void) -> NSURLSessionDataTask
returns data, response and error directly in a completion handler.
public func dataTaskWithRequest(request: NSURLRequest) -> NSURLSessionDataTask
is used in conjunction with the URLSessionDataDelegate protocol. A couple of methods are required to be implemented. During the several stages the delegate methods are called to process the data.
The protocol method provides finer control of the loading process, for example to handle credential requests and redirection control.