如何调用操作队列？

Question

尝试从ClassA解析Json文件并在ClassB中获取结果。

ClassB在ViewDidLoad（）上调用getResultfromA（）方法;它从ClassA获取解析结果，然后显示在与ClassB

关联的标签视图中

问题部分： - 结果在ClassB中打印为nil，但在一秒左右后，解析后的结果将打印在ClassA中，

结论： - 据我所知，我在异步任务中做了一些愚蠢的事情，它应该让ClassB中的任务等到从ClassA收到数据，这就是所期望的最终结果应该是

  ClassA () {

    func getJsonBookDetails(isbnString:String) -> Dictionary<String, String>{

    var gBooks = Dictionary<String, String>()
    let scriptUrl = "https://www.googleapis.com/books/v1/volumes?q=isbn:" + isbnString

    let myurl = URL(string:scriptUrl)
    let request = NSMutableURLRequest(url: myurl!)
    request.httpMethod = "GET"

    let task = URLSession.shared.dataTask(with: myurl! ) { (data, response, error) in
    if error != nil{
        print("THIS ERROR",error!)
        return
        } else{
        if let mydata = data{
            do{
                let myJson = try (JSONSerialization.jsonObject(with: mydata, options: JSONSerialization.ReadingOptions.mutableContainers)) as AnyObject

                if let dictonary = myJson["items"] as? NSArray {
                --/* parsed results stored in dictionary gBooks*/---                       
               }
                /* trying to send dictionary gBooks to  ClassB */
                var  myVar = ClassB()                  
                OperationQueue.addOperation() 
               /*  */
              } catch{
                print("Error found")
            }
           }      
        }
    }
task.resume()    
return gBooks
   }
}

这适用于ClassB，其结果是显示的

 ClassB {
       var userGbook = [String:String]()

        override func viewDidLoad() {
        super.viewDidLoad()
        getResultfromB()
       }

 func getResultfromA(){
    /* call func getJsonBookDetails() from classA and store in 
    userGbook /*
   /* display the result stored in associated labels using the keys form the dictionary */ 
    }
 }