Completion handler for Post to server - swift

Question

I found this awesome answer to posting data to php
The only problem is, I don't know how to return the data upon completion.
How can I make a completion handler for the following function?
func postToServer(postURL: String, postString: String) {
let request = NSMutableURLRequest(URL: NSURL(string: postURL)!)
request.HTTPMethod = "POST"
request.HTTPBody = postString.dataUsingEncoding(NSUTF8StringEncoding)
let task = NSURLSession.sharedSession().dataTaskWithRequest(request){
data, response, error in
let responseString = String(data: data!, encoding: NSUTF8StringEncoding)
if responseString != nil {
print("responseString = \(responseString!)")
}
}
task.resume()
}
Edit: Maybe I didn't apply it correctly, but the suggested duplicate link did not solve my problem. Could somebody please provide an example of this? I've been stuck on this for like 3 weeks now. I just don't know how to pull the data from task when it's completed. I've been reading up a lot on closures, but I just don't see where or even how these are related. When I try to find functions related to task, it only gives response...and that returns nil if I don't type in sleep(3) after resume.
I've watched a bunch of videos where people have the same code as me and don't use a completion handler and still get data back... what gives?

Answer 1

This works in swift 3
func postToServer(_ completion:#escaping (( _ response: String, _ success: Bool )-> Void), postURL: String, postString: String) {
let request = NSMutableURLRequest(url: NSURL(string: postURL)! as URL)
request.httpMethod = "POST"
request.httpBody = postString.data(using: String.Encoding.utf8)
let task = URLSession.shared.dataTask(with: request as URLRequest){
data, response, error in
let responseString = String(data: data!, encoding: String.Encoding.utf8)
if responseString != nil {
print("responseString = \(responseString!)")
completion(responseString!, true)
}
}
task.resume()
}
}