Run code after loop in background ends - xcode

Question

I am running background thread in a while loop where I am doing some file handling task. I have some code after the loop. But the codes after the loop being executed before the loop ends (cause I am using background thread). Is there any way I can execute some code exactly after the loop ends?
Here is my code:
while i < testCount {
let task = AsyncTask(
backgroundTask: {
() -> Double in
// some file handling
return 234.09
},
afterTask: {
(val: Double) in
self.showVal(val)
}
);
task.execute();
i += 1
}
// I want to run this code after the loop ends
print("average: \(avg)")
showVal(avg)
My showVal(Double) function
func showVal(val: Double) {
print("val found: \(val)")
display.text = "\(val) found"
}
And here is my AsyncTask class
public class AsyncTask <BGParam,BGResult>{
private var pre:(()->())?;//Optional closure -> called before the backgroundTask
private var bgTask:(param:BGParam)->BGResult;//background task
private var post:((param:BGResult)->())?;//Optional closure -> called after the backgroundTask
public init(beforeTask: (()->())?=nil, backgroundTask: (param:BGParam)->BGResult, afterTask:((param:BGResult)->())?=nil){
self.pre=beforeTask;
self.bgTask=backgroundTask;
self.post=afterTask;
}
public func execute(param:BGParam){
pre?()//if beforeTask exists - invoke it before bgTask
dispatch_async(dispatch_get_global_queue(QOS_CLASS_BACKGROUND, 0), {
let bgResult=self.bgTask(param: param);//execute backgroundTask in background thread
if(self.post != nil){//if afterTask exists - invoke it in UI thread after bgTask
dispatch_async(dispatch_get_main_queue(),{self.post!(param: bgResult)});
}
});
}
}
Note: I am a beginner in Swift.
Edit:
I actually want to do:
A background file handling task
After the task ends, I want to show a text in a UILabel
I need to do this two tasks several times (say 100 times). If swift has easier methods for my purpose, please advise.

Answer 1

I'll try with some pseudo-code based our discussion to see if that might help you on the way. The manager-object would probably look a little something like this:
class RequestManager {
private let requiredNumberOfRequests: Int
private let completionHandler: ()->()
private var counter: Int {
didSet {
if counter == requiredNumberOfRequests {
completionHandler()
}
}
}
init(numberOfRequests: Int, completionHandler: ()->()) {
self.requiredNumberOfRequests = numberOfRequests
self.completionHandler = completionHandler
self.counter = 0
}
// Don't know exactly what you want to do here, but something like...
func performRequest(success: (value: Double)->()) {
// Network stuff, on success it looks like you'll have a Double(?)
let value: Double = 234.09
success(value: value)
counter += 1
}
}
Then, before your loop you'll create an instance of the requestManager
let manager = RequestManager(numberOfRequests: 100) { average in
print("average: \(average)")
}
...and call the performRequest as part of your loop.