Why is retrieving data from JSON taking a lot of time? - json

Question

It takes at least 15-35 second for my iPhone to go through these loops. I learned about JSON mostly on StackOverflow and this is the way people do this. These arrays have 3 elements inside with some text and one small image per element
if let parseJSON = json{
let succes = parseJSON["data"]
let item = self.success["catalogue_products"] as! [[String: AnyObject]]
if item.isEmpty == false{
for i in item {
var categoryName = i["category_name"] as! String
if self.category == nil{
self.category = categoryName
self.categories.append(self.category)
self.categoryCount = 1
}
if self.category != categoryName{
self.categoryCount += 1
self.category = categoryName
self.categories.append(self.category)
}
var deep = i["products"] as! [[String: AnyObject]]
for i in deep{
var product = ProductCatalogue()
product.categoryName = categoryName
product.id = i["id"]
println(product.id)
product.name = i["name"]
product.imageUrl = i["image"]
product.value = i["value"]
var volumes = (i["volumes"] as? [AnyObject])!
var check = true
for i in volumes{
if check == true {
product.volumeMin = i
check = false
} else {
product.volumeMax = i
check = true
}
}
product.colors = i["colors"] as! [[String: AnyObject]]
for i in product.colors{
let temp: AnyObject? = i["code"]
product.colorCode.append(temp!)
let url2: AnyObject? = i["image"]
product.colorImageUrl.append(url2!)
}
let url = NSURL(string: String(stringInterpolationSegment: product.imageUrl))
let data = NSData(contentsOfURL: url!)
product.image = UIImage(data: data!)
if product.colorImageUrl.isEmpty == false {
for i in 0...(product.colorImageUrl.count - 1) {
let url1 = NSURL(string: String(stringInterpolationSegment: product.colorImageUrl[i]))
let data1 = NSData(contentsOfURL: url1!)
switch i {
case 0: product.color1 = UIImage(data: data1!)
case 1: product.color2 = UIImage(data: data1!)
case 2: product.color3 = UIImage(data: data1!)
case 3: product.color4 = UIImage(data: data1!)
case 4: product.color5 = UIImage(data: data1!)
case 5: product.color6 = UIImage(data: data1!)
case 6: product.color7 = UIImage(data: data1!)
default: println("")
}
}
}
self.array.append(product)
}
}
self.sortinOut()
self.loadScreen()

Answer 1

Its because you are making MANY HTTP requests. First in one for loop which is not a good idea at all and second time in the nested loop, which in my idea is a bad mistake. HTTP requests are not efficient and fast when dealing them like this.
If you are willing to get a bunch of data, make the JSON in your REST api and get it once.
If you don't have a REST api and you're simply getting images from the web, make it as efficient as possible by making the fewest requests possible. Also, try getting your images Asynchronously, by calling the GCD Async function.
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
// download image
});
Hope it helps