class FirstViewController: TFBaseViewController {

    var ljload :LJDownLoadNetImage?  //声明
    
    
    override func viewDidLoad() {
        super.viewDidLoad()

        self.view.backgroundColor = UIColor.white
        self.setTopNavBarTitle("首页")
         ljload = LJDownLoadNetImage()
        self.initTest()
    }

    //MARK: 点击事件
    func buttonClick(_ sender:UIButton)
    {
        //避免循环引用，weak当对象销毁的时候，对象会被指定为nil
        //weak var weakSelf = self //对象推到，省略了ViewController
        weak var weakSelf : FirstViewController? = self  //等同与上面的表达式
        ／／数据回调
        ljload?.loadData({ (jsonData:String) in
            print("获取到的数据:\(jsonData)")
            
            weakSelf?.view.backgroundColor = UIColor.red
        })
       
        //let vc = TFNetImageViewController()
        //self.navigationController?.pushViewController(vc,animated: true)
    }

import Foundation

class LJDownLoadNetImage: NSObject {
   
    //闭包类型 （参数列表）->(返回值类型)
    func loadData(_ finishCallBack: @escaping (_ jsonData:String) -> ()) {
        //1. 发送异步网络请求
        //放在此处，可以不加@escaping
//         finishCallBack()
     
        if #available(iOS 8.0,*) {
            DispatchQueue.global().async { 
                print("发送异步网络请求")
                
                DispatchQueue.main.async(execute: {
                    
                    //放在此处必须要加@escaping
                    finishCallBack("jsonData")
                })
            }
        }
    }
}

控制台打印的数据

@H_404_19@发送异步网络请求

@H_404_19@获取到的数据@H_404_19@:jsonData