NSURLSession didReceiveData not being triggered - swift

Question

I'm having a problem detecting when data is being received using NSURLSession. The equivalent code with NSURLConnection does work, but that's not included here.
In this example, I'm doing a request to google.com. The completionHandler works and "complete" is printed (also the data, etc if you change the code).
However didReceiveData isn't triggered and "received data" is never printed.
I've been through the docs and done a ton of searching and I think this looks right, but I can't seem to get it to work. Definitely would appreciate any help with this.
(I need to use didReceiveData because I'm going to parsing a streaming json api.)
Thanks!
import UIKit
class ViewController: UIViewController, NSURLSessionDelegate, NSURLSessionDataDelegate, NSURLSessionTaskDelegate {
override func viewDidAppear(animated: Bool) {
let session = NSURLSession.sharedSession()
var task = session.dataTaskWithURL(NSURL(string: "https://google.com")!, completionHandler: { (data, response, error) -> Void in
print("complete")
})
task.resume()
}
func URLSession(session: NSURLSession, dataTask: NSURLSessionDataTask, didReceiveData data: NSData) {
print("received data")
}
}

Answer 1

There were two issues.
When the session is created, you must define a delegate. That was the main reason didReceiveData wasn't being called.
The second issue is that if you use a completionHandler block, then all the delegates functions are bypassed. In the code for NSURlSession, it says
extension NSURLSession {
/*
* data task convenience methods. These methods create tasks that
* bypass the normal delegate calls for response and data delivery,
* and provide a simple cancelable asynchronous interface to receiving
* data. Errors will be returned in the NSURLErrorDomain,
* see <Foundation/NSURLError.h>. The delegate, if any, will still be
* called for authentication challenges.
*/
You must implement each delegate function you need to check for completion, errors, etc.
The updated code is below:
import UIKit
class ViewController: UIViewController, NSURLSessionDelegate {
override func viewDidAppear(animated: Bool) {
let config = NSURLSessionConfiguration.defaultSessionConfiguration()
let session = NSURLSession(configuration: config, delegate: self, delegateQueue: nil)
var task = session.dataTaskWithURL(NSURL(string: "https://google.com")!)
task.resume()
}
func URLSession(session: NSURLSession, dataTask: NSURLSessionDataTask, didReceiveData data: NSData) {
print("received data")
}
}

Answer 2

You can get data in completionHandler only. Why do you want to use didReceiveData?
Below code will show you how you can get the received data
override func viewDidAppear(animated: Bool) {
let session = NSURLSession.sharedSession()
var task = session.dataTaskWithURL(NSURL(string: "https://google.com")!, completionHandler: { (data, response, error) -> Void in
if NSJSONSerialization.isValidJSONObject(data){
if let jsonParam = try? NSJSONSerialization.dataWithJSONObject(dictData, options: []){
print("Result Data : \(jsonParam)")
}
}
})
task.resume()
}