NSURLSession.sharedSession().dataTaskWithRequest(request) being executed last - ios

Question

I'm having a problem with NSURLSession.sharedSession().dataTaskWithRequest(request). I want to authenticate my app against some API and if the authentication is successful then the app will let the user to authorise health kit and finally fetch some data from there.
I have this in my viewDidLoad()
print ("AUTHORIZING APIGEE!!!")
authorizeApigee()
if (self.errorApigee == 0) {
print ("APIGEE AUTHORIZED!")
// We cannot access the user's HealthKit data without specific permission.
print ("AUTHORIZING HEALTHKIT!!")
getHealthKitPermission()
print ("HEALTHKIT AUTORIZED!")
} else {
print ("APIGEE UNAUTHORIZED!")
}
and this is the authorising function:
// Authenticating app with Apigee Health APIx
func authorizeApigee(){
// Send HTTP GET Request
let scriptUrl = "https://fhirsandbox-prod.apigee.net/oauth/v2"
let urlWithParams = scriptUrl + "/accesstoken?grant_type=client_credentials"
let myUrl = NSURL(string: urlWithParams);
let request = NSMutableURLRequest(URL:myUrl!);
request.HTTPMethod = "POST"
// Add Basic Authorization
let username = "****"
let password = "****"
let loginString = NSString(format: "%#:%#", username, password)
let loginData: NSData = loginString.dataUsingEncoding(NSUTF8StringEncoding)!
let base64LoginString = loginData.base64EncodedStringWithOptions(NSDataBase64EncodingOptions())
request.setValue(base64LoginString, forHTTPHeaderField: "Authorization")
let task = NSURLSession.sharedSession().dataTaskWithRequest(request) {
data, response, error in
// Check for error
if error != nil
{
self.errorApigee = 1
print("error=\(error)")
return
}
// Print out response string
let responseString = NSString(data: data!, encoding: NSUTF8StringEncoding)
print("responseString = \(responseString)")
}
task.resume()
}
The problem is that even though authorizeApigee() is called, the app stops at NSURLSession.sharedSession().dataTaskWithRequest(request), goes out of the function, obviously errorApigee variable is not updated and therefore it goes to the next step of authorising health kit without authorising Apigee. Finally when health kit was authorised it goes back and authorises Apigee.
Any idea why this might happen at all?
Any tip would be greatly appreciated!

Answer 1

This is simple example how to use completion :
func authorizeApigee(completion: (auth: Bool) -> Void) {
// Send HTTP GET Request
let scriptUrl = "https://fhirsandbox-prod.apigee.net/oauth/v2"
let urlWithParams = scriptUrl + "/accesstoken?grant_type=client_credentials"
let myUrl = NSURL(string: urlWithParams);
let request = NSMutableURLRequest(URL:myUrl!);
request.HTTPMethod = "POST"
// Add Basic Authorization
let username = "****"
let password = "****"
let loginString = NSString(format: "%#:%#", username, password)
let loginData: NSData = loginString.dataUsingEncoding(NSUTF8StringEncoding)!
let base64LoginString = loginData.base64EncodedStringWithOptions(NSDataBase64EncodingOptions())
request.setValue(base64LoginString, forHTTPHeaderField: "Authorization")
let task = NSURLSession.sharedSession().dataTaskWithRequest(request) {
data, response, error in
// Check for error
if error != nil
{
self.errorApigee = 1
print("error=\(error)")
completion(auth: false)
}
// Print out response string
let responseString = NSString(data: data!, encoding: NSUTF8StringEncoding)
print("responseString = \(responseString)")
completion(auth: true)
}
task.resume()
}
And how to use :
self.authorizeApigee { (auth) -> Void in
if (auth) {
getHealthKitPermission()
} else {
//print errors
}
}

Answer 2

NSURLSession.sharedSession().dataTaskWithRequest() is executed in another thread. It's so that the main application thread doesn't hang and wait for the request to complete. If you want a code block to run after the async task is complete, I suggest you use a completion block.

Answer 3

You need to use closure because api calling work in async manner so first change your function definition like this
func authorizeApigee(completion: (Int) -> ()){
let scriptUrl = "https://fhirsandbox-prod.apigee.net/oauth/v2"
let urlWithParams = scriptUrl + "/accesstoken?grant_type=client_credentials"
let myUrl = NSURL(string: urlWithParams);
let request = NSMutableURLRequest(URL:myUrl!);
request.HTTPMethod = "POST"
// Add Basic Authorization
let username = "****"
let password = "****"
let loginString = NSString(format: "%#:%#", username, password)
let loginData: NSData = loginString.dataUsingEncoding(NSUTF8StringEncoding)!
let base64LoginString = loginData.base64EncodedStringWithOptions(NSDataBase64EncodingOptions())
request.setValue(base64LoginString, forHTTPHeaderField: "Authorization")
let task = NSURLSession.sharedSession().dataTaskWithRequest(request) {
data, response, error in
// Check for error
if error != nil
{
completion(0)
print("error=\(error)")
return
}
// Print out response string
let responseString = NSString(data: data!, encoding: NSUTF8StringEncoding)
print("responseString = \(responseString)")
completion(1)
}
task.resume()
}
Now call your function like this
self.authorizeApigee() { (result) -> () in
if result == 0 {
print ("APIGEE AUTHORIZED!")
// We cannot access the user's HealthKit data without specific permission.
print ("AUTHORIZING HEALTHKIT!!")
getHealthKitPermission()
print ("HEALTHKIT AUTORIZED!")
} else {
print ("APIGEE UNAUTHORIZED!")
}
}