Make instance wait until called functions are complete - Swift - ios

Question

I apologise in advance if this has already been answered but as you can probably tell from the title I wasn't really sure how to describe the issue and a answer to a similar question I found wasn't helpful.
I'm attempting to make an instance of "Coupon" that has its properties loaded from an SQL database after passing an id to the database in the init method.
My issue is when I call then init method from a different viewController class it will return the instance with the default string values of "" as the data from the NSURLConnection hasn't been/decoded before returning to the viewContoller.
Im looking for a solution for to some how make the init method wait until the fields are loaded.
Coupon class relevant properties:
var webData: NSMutableData?
var id: Int
var name: String = ""
var provider: String = ""
var details: String = ""
Coupon class relevant methods:
convenience init(id: Int) {
self.init()
self.id = id
self.selectSQL(id) //passes id to server and returns all other varibles
}
func selectSQL(id: Int) {
let url = NSURL(string: "http://wwww.website.php?id=\(id)") // acess php page
let urlRequest = NSURLRequest(URL: url!)
let connection = NSURLConnection(request: urlRequest, delegate: self)
}
func connection(connection: NSURLConnection, didReceiveResponse response: NSURLResponse) {
webData = NSMutableData()
}
func connection(connection: NSURLConnection, didReceiveData data: NSData) {
webData?.appendData(data)
}
func connectionDidFinishLoading(connection: NSURLConnection) {
let result = NSJSONSerialization.JSONObjectWithData(webData!, options: .AllowFragments, error: nil) as? NSArray
let resultDict = result?[0] as? NSDictionary
if let dict = resultDict {
name = dict.objectForKey("name") as! String
provider = dict.objectForKey("provider") as! String
details = dict.objectForKey("details") as! String
}

Answer 1

It is not possible to "wait for your SQL finishing" and then return from init without blocking your thread (synchronize), which would not be what you want.
I suggest to use a factory method with a callback to get a workaround for it. Like this:
class Coupon {
private var handler: ((coupon: Coupon) -> ())?
class func createCoupon(id: Int, completionHandler: ((coupon: Coupon) -> ())?) {
let coupon = Coupon(id: id)
// Store the handler in coupon
coupon.handler = completionHandler
}
//...
func connectionDidFinishLoading(connection: NSURLConnection) {
//...Setup coupon properties
handler?(coupon: self)
handler = nil
}
}
Then you can create and use your coupon like this:
Coupon.createCoupon(1, completionHandler: { (coupon) -> () in
// Do your thing with fully "inited" coupon
})
Of course, you also need to consider the situation of connection failed to your server, and maybe call the handler with an error, which does not present in your current code.