//    闭包类型 首先写(参数列表)->(返回值类型)
    func loadData(callBack : (jsonData:String)->()){
        
        dispatch_async(dispatch_get_global_queue(0, 0)) { 
            print("网络请求\(NSThread.currentThread())")
            
            dispatch_sync(dispatch_get_main_queue(), { 
                print("获取到数据\(NSThread.currentThread())")
                callBack(jsonData: "数据")
            })
        }
    }