Function completes before NSURLSession - dataTaskWithRequest completed [duplicate] - ios

Question

This question already has an answer here:
NSURLConnection sendAsynchronousRequest can't get variable out of closure
(1 answer)
Closed 7 years ago.
I have the following method called under ViewDidLoad(). I understand that session.dataTaskWithRequest automatically runs in background thread. And because of the same, the code following this method in ViewDidLoad() does not wait for this process to complete and starts executing.
Is there any way that I can ensure that the background thread is completed before other methods are executed?
func getCoordinatesFromServer() {
let request = NSMutableURLRequest(URL: NSURL(string: constants.urlName.loadData)!)
request.HTTPMethod = "POST"
request.addValue("multipart/form-data", forHTTPHeaderField: "Accept")
request.setValue("keep-Alive", forHTTPHeaderField: "Connection")
request.HTTPBody = (constants.requestTag.getCoordinates).data
let session = NSURLSession.sharedSession()
let task = session.dataTaskWithRequest(request, completionHandler: {(data, response ,error ) in
if let response = response {
let httpResponse = response as! NSHTTPURLResponse
print("response code = \(httpResponse.statusCode)")
if (httpResponse.statusCode == 200) {
dispatch_async(dispatch_get_main_queue(), {
let decodedData = NSData(base64EncodedData: data!, options: NSDataBase64DecodingOptions([]))
let jsonText = NSString(data: decodedData!, encoding: NSASCIIStringEncoding) as! String
do {
let json = try NSJSONSerialization.JSONObjectWithData(jsonText.data, options: NSJSONReadingOptions.init(rawValue: 0))
self.parseJsonData(json["Datalist"] as! NSArray)
} catch {
print("Error:\n \(error)")
}
})
}
}
})
task.resume()
}
Regards,

Answer 1

if I understand your question, you can solve this problem at this way
For example:
class func ConnectedToNetwork(completionHandler: ((Status: Bool) -> Void))
{
let url = NSURL(string: "http://google.com")
let request = NSMutableURLRequest(URL: url!)
request.HTTPMethod = "HEAD"
request.timeoutInterval = 0.2
let task = NSURLSession.sharedSession().dataTaskWithURL(url!) {(data,response, error) in
let httpResponse = response as! NSHTTPURLResponse
if httpResponse.statusCode == 200
{ completionHandler(Status: true)
return
}
}
task.resume()
}
and then, you can work with this
Checks.ConnectedToNetwork({ Status in dispatch_async(dispatch_get_main_queue())
{
if Status == true
{
//do what you want
}
});

Answer 2

dataTaskWithRequest is assync call, and it has completionHandler block. So all code that you wrote inside will be executed after the data task finished:
let request = NSURLRequest(URL: NSURL(string: "http://google.com")!)
let task = NSURLSession.sharedSession().dataTaskWithRequest(request, completionHandler: {(data, response ,error ) in
print("3") // executed after data task is finished
print("4") // executed after data task is finished
})
task.resume()
print("1")
print("2")

Answer 3

import Foundation
// some aync function with completition handler, i MUST USE AS IT IS
func f(completitionHandler: ()->()) {
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0)) { () -> Void in
print("running concurrently")
sleep(1)
print("finished")
completitionHandler()
}
}
// some function running on main queue
func foo() {
// create dispatch group
let group = dispatch_group_create()
let myCompletitionHandler: ()->() = {
dispatch_group_leave(group)
}
let queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0)
dispatch_group_async(group, queue) { () -> Void in
dispatch_group_enter(group)
f(myCompletitionHandler)
}
dispatch_group_wait(group, DISPATCH_TIME_FOREVER)
}
foo()
print("foo finished")
It is not the best at all, the better solution is to run synchronous version of f() instead of this 'workaround':-)