How to download image from asynchronously in swift - ios

Question

Hi I am developing a app using swift2.2 am getting a data from a server and am passing it to the collection view.am getting more images from the server i cant pass it very quickly it consumes so much of time so i need to to pass that quickly as much as possible.
code in my view controller:
func jsonParsingFromURL() {
self.view.makeToastActivity(.Center)
if Reachability.isConnectedToNetwork() == true {
Alamofire.request(.POST, "http://something.com=\(appDelCityname)&fromLimit=0&toLimit=20", parameters: nil, encoding: .URL, headers: nil).response {
(req, res, data, error) - > Void in
let dataString = NSString(data: data!, encoding: NSUTF8StringEncoding)
print(dataString)
let json = JSON(data: data!)
let jsonData = json["ad_count"].int
if jsonData == 0 {
let alert = UIAlertController(title: "sorry!", message: "No Ads availabe", preferredStyle: UIAlertControllerStyle.Alert)
alert.addAction(UIAlertAction(title: "OK", style: UIAlertActionStyle.Default, handler: nil))
self.presentViewController(alert, animated: true, completion: nil)
} else {
self.startParsing(data!)
}
}
} else {
let alert = UIAlertController(title: "No Internet Connection", message: "make sure your device is connected to the internet", preferredStyle: UIAlertControllerStyle.Alert)
alert.addAction(UIAlertAction(title: "OK", style: UIAlertActionStyle.Default, handler: nil))
self.presentViewController(alert, animated: true, completion: nil)
}
}
func startParsing(data: NSData) {
let json = JSON(data: data)
let mainArr = json["subcategory"].array!
for item in mainArr {
self.fetchImage = item["images"].stringValue
self.fetchPrice = item["originalprice"].stringValue
self.fetchTitle = item["adtitle"].stringValue
self.fetchCityname = item["districtname"].stringValue
let takefirstImg = self.fetchImage.componentsSeparatedByString(",")
let firstimgofStr = takefirstImg[0]
dispatch_async(dispatch_get_main_queue(), {
() - > Void in
let URL_API_HOST2: String = "https://www.something.com"
let url = NSURL(string: URL_API_HOST2 + firstimgofStr)
let data = NSData(contentsOfURL: url!)
let imageyy = UIImage(data: data!)
self.priceArr.append(self.fetchPrice)
self.cityArr.append(self.fetchCityname)
self.adtitleArr.append(self.fetchTitle)
print("something = \(firstimgofStr)")
print("check image = \(self.fetchTitle)")
self.imageDict.append(imageyy!)
self.view.hideToastActivity()
})
self.refresh()
}
}
func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) - > Int {
return imageDict.count
}
func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) - > UICollectionViewCell {
let cell = collectionView.dequeueReusableCellWithReuseIdentifier("FilterCell", forIndexPath: indexPath) as!SecondTableViewCell
cell.FifTitle.text = adtitleArr[indexPath.item]
cell.FifAddress.text = cityArr[indexPath.item]
cell.Fifprice.text = priceArr[indexPath.item]
dispatch_async(dispatch_get_main_queue(), {
cell.Fifimage.image = self.imageDict[indexPath.item]
})
// cell.Fifimage.sd_setImageWithURL(NSURL(string: URL_API_HOST2 + (firstImage as String)))
return cell
}
func collectionView(collectionView: UICollectionView, layout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: NSIndexPath) - > CGSize {
return imageDict[indexPath.item].size
}
I am having the library of SDWebImage but which will allow only url type but i have to use UIImage value to calculate the size of image to get Pinterest style view.according to my method it works well but when i get more value from the server it makes very late to display so help me to work with this process am struggling from the morning.