Can't fetch data from API Closure

Question

I am a beginner in Swift. I am trying to make app to fetch data from a Django server, but I'm stuck in fetch data from Closure, my code is as below:

var datasource: [Vender] = []

override func vieDidLoad() {
   super.viewDidLoad() 
   loaddata()
   print(datasource) //#1 print
}
 
func loadata(){ 
    VenderAPI(method: "GET", endpoint: "vender", APIportocol: Vender(), index: "") {
    Result in 
      switch Result {
        case .failure(let error):
          print(error.localizedDescription)
        case .success(let APIdata):
          for data in APIdata {
            self.datasource.append(data)
         }
     }
  print(self.datasource) //#2 print
}

My question is, I can get #2 print (correct data and format from server), but not #1 print (always empty). Can somebody help me? I will so appreciate.

Answer 1

as @Larme mentioned, you need to deal with the asynchronous function. Read-up about it. Try this approach:

override func viewDidLoad() {
    super.viewDidLoad()
    loaddata() { done in  // <--- here
        print(datasource) // print when all work is done
    }
}
 
func loadata(completion: @escaping(Bool) -> ()) {  // <--- here
    VenderAPI(method: "GET", endpoint: "vender", APIportocol: Vender(), index: "") {
        result in
        switch result {
        case .failure(let error):
            print(error.localizedDescription)
        case .success(let APIdata):
            for data in APIdata {
                self.datasource.append(data)
            }
        }
        completion(true)  // <--- here
    }
}