Swift 2.0: HTTP GET error handling in Xcode 7 - http

Question

I'm new with xcode programming, I'm trying to implement an App in Swift 2 that makes an HTTP Get request. After upgrading xcode 7 its showing error of:
Cannot convert value of type
'(NSData!, response: NSURLResponse!, err: NSError!) -> ()'
to expected argument type
'(NSData?, NSURLResponse?, NSError?) -> Void'
(This code snippet uses the old error handling of swift 1.2.) Can anyone help me please how to implement this in Swift 2.0.
request.HTTPMethod = "GET"
let session = NSURLSession.sharedSession()
let task = session.dataTaskWithRequest(request, completionHandler:loadedData)
task.resume()
}
func loadedData(data:NSData!, response:NSURLResponse!, err:NSError!){
if(err != nil)
{
print(err?.description)
}
else
{
var jsonResult: NSDictionary = NSDictionary()
let httpResponse = response as! NSHTTPURLResponse
print("\(httpResponse.statusCode)")
if (httpResponse.statusCode == 200)
{
jsonResult = (try! NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableContainers)) as! NSDictionary
print(jsonResult)
self.performSegueWithIdentifier("SuccessSignin", sender: self)
}
else if (httpResponse.statusCode == 422){
print("422 Error Occured...")
}
}
}

Answer 1

The method signature has changed (parameters are now optionals). Also, you have to use try enclosed in a do catch block. And avoid using forced try (with !) but prefer catching possible errors, and use if let to safely unwrap optionals. Example:
let task = session.dataTaskWithRequest(request) { (data, response, error) -> Void in
if error != nil {
print(error!.description)
} else {
if let httpResponse = response as? NSHTTPURLResponse {
if httpResponse.statusCode == 200 {
do {
if let data = data, let jsonResult = try NSJSONSerialization.JSONObjectWithData(data, options: []) as? NSDictionary {
print(jsonResult)
self.performSegueWithIdentifier("SuccessSignin", sender: self)
}
} catch let JSONError as NSError {
print(JSONError)
}
} else if (httpResponse.statusCode == 422) {
print("422 Error Occured...")
}
} else {
print("Can't cast response to NSHTTPURLResponse")
}
}
}
task.resume()

Answer 2

Here's the error message that you are receiving:
Cannot convert value of type
'(NSData!, response: NSURLResponse!, err: NSError!) -> ()'
to expected argument type
'(NSData?, NSURLResponse?, NSError?) -> Void'
As is shown in the message, the parameters for the dataTaskWithRequest's completionHandler changed from being forced unwrapped (!) to being just optionals (?).
Notice the ! versus the ?:
// old
(NSData!, response: NSURLResponse!, err: NSError!)
// new
(NSData?, NSURLResponse?, NSError?)
As a result, you need to adjust your code accordingly.
For example, your method declaration will look like this:
func loadedData(data:NSData?, response:NSURLResponse?, err:NSError?)
In addition, evaluate the method body and make sure that you are now properly unwrapping the optional parameters data, response and err.
See the NSURLSession class reference for more information.