Slow JSONSerialization Parsing Swift 3.0 - swift

Question

I'm building an application able to return books info (Title,Description,Author ...) using Google Books Api.
The problem is that after detecting ISBN (International Standard Book Number)from the previous view it takes time to show details on my current view.
After 1-3 seconds I get parsing result:
I'm using this method to get data using google books api:
func getBookInfo(isbn: String) {
guard let url = URL(string: "https://www.googleapis.com/books/v1/volumes?q=isbn:\(isbn)") else {
print("***********************************")
print("the url is not valid")
return
}
URLSession.shared.dataTask(with: url, completionHandler: {data, response, error -> Void in
guard error == nil else {
print(response)
print(error!.localizedDescription)
return
}
guard let data = data else {
print("no error but no data")
print("***********************************")
print(response)
return
}
guard let jsonResult = try? JSONSerialization.jsonObject(with: data, options: []) else {
print("the JSON is not valid")
return
}
if let arrayOfLa = (jsonResult as AnyObject).value(forKeyPath: "items.volumeInfo.language") as? [String] {
DispatchQueue.global(qos: .userInitiated).async {
// Bounce back to the main thread to update the UI
DispatchQueue.main.async {
print("opopopop")
print (arrayOfLa)
}
}
}
///finish language
if let arrayOfTitles = (jsonResult as AnyObject).value(forKeyPath: "items.volumeInfo.title") as? [String] {
DispatchQueue.global(qos: .userInitiated).async {
// Bounce back to the main thread to update the UI
DispatchQueue.main.async {
self.title = "\(arrayOfTitles[0])"
}
}
}
if let arrayOfDesc = (jsonResult as AnyObject).value(forKeyPath: "items.volumeInfo.description") as? [String] {
DispatchQueue.global(qos: .userInitiated).async {
// Bounce back to the main thread to update the UI
DispatchQueue.main.async {
self.bookDescription.text = "\(arrayOfDesc[0])"
}
}
}
//start here
if let arrayOfPictures = (jsonResult as AnyObject).value(forKeyPath: "items.volumeInfo.imageLinks.thumbnail") as? [String] {
print ("\(arrayOfPictures[0])")
self.bookPicture = "\(arrayOfPictures[0])"
if let checkedUrl = URL(string: "\(arrayOfPictures[0])") {
self.imageBook.contentMode = .scaleAspectFit
self.downloadImage(url: checkedUrl)
}
}
//end here
//start author here
if let arrayOfAuthors = (jsonResult as AnyObject).value(forKeyPath: "items.volumeInfo.authors") as? [[String]] {
DispatchQueue.global(qos: .userInitiated).async {
// Bounce back to the main thread to update the UI
DispatchQueue.main.async {
self.authorText.text = "\((arrayOfAuthors[0])[0])"
}
}
}
// finish author here
//start categories here
if let arrayOfCategories = (jsonResult as AnyObject).value(forKeyPath: "items.volumeInfo.categories") as? [[String]] {
DispatchQueue.global(qos: .userInitiated).async {
// Bounce back to the main thread to update the UI
DispatchQueue.main.async {
self.categorieText.text = "\((arrayOfCategories[0])[0])" }
}
}
// finish caetegories here
}).resume()
}
and I'm calling it on the ViewWillAppaer
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
getBookInfo(isbn: isbnCode)
}
Any suggestions ?