Download JSON Data THEN Reload Collection View - ios

Question

Quick one here. I have a class called NetworkService. It has a method that sets up an NSURLSession and completion block. My Object class, NewsItem, has a method downloadNewsItems that calls the first method and goes to a url, downloads JSON data, appends it to an array and returns it. up until that point everything works as i'd want. I create the object and append it then return it (the method is named downloadImage but it can work with any sort of data).
func downloadImage(completion: (NSData -> Void)) {
let request = NSURLRequest(URL: self.url)
let dataTask = session.dataTaskWithRequest(request) { (data, response, error) in
if error == nil {
if let httpResponse = response as? NSHTTPURLResponse {
switch (httpResponse.statusCode) {
case 200:
if let data = data {
completion(data)
}
default:
print(httpResponse.statusCode)
}
}
} else {
print("Error: \(error?.localizedDescription)")
}
}
dataTask.resume()
}
here's the implementation of the same method on my object class.
static func downloadNewsItems() -> [NewsItem] {
var newsItems = [NewsItem]()
let url = NSURL(string: "http://my-url.com.json")
let networkService = NetworkService(url: url!)
networkService.downloadImage { (data) -> Void in
let jsonData = JSON(data:data)
for item in jsonData["stories"].arrayValue {
// print(item["title"])
let newsArticle = NewsItem()
newsArticle.category = item["category"].string
newsArticle.titleText = item["title"].string
newsArticle.paragraph1 = item["paragraph1"].string
newsArticle.paragraph2 = item["paragraph2"].string
newsArticle.featureImage = NSURL(string: "\(item["headerImage"].string)")
newsArticle.date = item["date"].string
newsArticle.majorReference = item["majorReference"].string
newsArticle.fact = item["fact"].string
newsItems.append(newsArticle)
}
print(newsItems.count)
}
return newsItems
}
That print(newsItems.count) shows I have downloaded and updated my objects properly into a dictionary. Now here comes the problem. I have a CollectionViewController. I want to populate it with the data I get from the method call. I create an array and call the method that returns the objects on it inside of ViewDidLoad: but NO! when I print, I get 0 and my collectionView doesn't display any cells.
var newsItems = [NewsItem]()
then in viewDidLoad:
newsItems = NewsItem.downloadNewsItems()
print(newsItems.count)
collectionView.reloadData()
The objects are downloaded, get set up by my init() method and are added to the array in the method whilst inside of the NetworkService / NewsItem classes but when I call the method from the Collection View Controller, Nothing. Initially I tried the default JSONSerialisation route but i had the same problem. I thought maybe I'm not doing it right. Switched to a 3rd party JSON Library (SwiftyJSON)... Exact SAME PROBLEM. Please help. I have had 3 weeks of this. I.. I can't. Not anymore..

Answer 1

user2361090,
You are making a webservice call to fetch all the newsItems inside downloadNewsItems. Which is an asynchronous call. So it takes a little bit of time to fetch process and then populate the newsItems array. But you are not waiting for it to get populated even before it gets populated you have returned it Hence you will return empty array in newsItems = NewsItem.downloadNewsItems(). Use blocks to handover the data. Change your method as
static func downloadNewsItems(completionBlock block : ([NewsItem]) -> ()){
var newsItems = [NewsItem]()
let url = NSURL(string: "http://my-url.com.json")
let networkService = NetworkService(url: url!)
networkService.downloadImage { (data) -> Void in
let jsonData = JSON(data:data)
for item in jsonData["stories"].arrayValue {
// print(item["title"])
let newsArticle = NewsItem()
newsArticle.category = item["category"].string
newsArticle.titleText = item["title"].string
newsArticle.paragraph1 = item["paragraph1"].string
newsArticle.paragraph2 = item["paragraph2"].string
newsArticle.featureImage = NSURL(string: "\(item["headerImage"].string)")
newsArticle.date = item["date"].string
newsArticle.majorReference = item["majorReference"].string
newsArticle.fact = item["fact"].string
newsItems.append(newsArticle)
}
print(newsItems.count)
//if the control comes here in background thread because you know you have to reload the collection view which is UI operation change it main thread
dispatch_async(dispatch_get_main_queue(), { () -> Void in
block(newsItems)
})
}
}
Finally you can call it as,
NewsItem.downloadNewsItems{ (passedArray) -> () in
newsItems = passedArray
collectionView.reloadData()
}