我的函数返回字符串但我无法解析它？知道为什么吗？

Question

我创建了一个名为db_conn 的类，在这个类中我有以下功能：

public func login (email : String , password : String ) -> String  {
    var result = ""
    let url = URL(string: API.url_login.rawValue)!
    var request = URLRequest(url: url)
    request.setValue("application/x-www-form-urlencoded", forHTTPHeaderField: "Content-Type")
    request.httpMethod = "POST"
    let postString = "email=\(email)&password=\(password)"
    request.httpBody = postString.data(using: .utf8)
    let task = URLSession.shared.dataTask(with: request) { data, response, error in


        guard let data = data, error == nil else {
            print("error=\(String(describing: error))")
            return
        }

        if let httpStatus = response as? HTTPURLResponse, httpStatus.statusCode != 200 {
            print("statusCode should be 200, but is \(httpStatus.statusCode)")
            print("\(String(describing: response))")
        }

        let responseString = String(data: data, encoding: .utf8)
        result = String(responseString!)
        //print("responseString = \(responseString!)")
    }
    task.resume()


    return result
}

然后在我的登录 viewController 类中，我尝试像 ==> 一样使用它

 @IBAction func login_button_action(_ sender: UIButton) {

       let email = email_text.text
       let passw0rd = password_text.text


        if (email != "" && passw0rd != ""){
            let db_connect = db_conn()
            if  (db_connect.login(email: email!, password: passw0rd!) == nil ){

                print("it's empty ")

            }else {

                print("not empty \(db_connect.login(email: email!, password: passw0rd!))")

            }


        }else {

            let alert = UIAlertController(title: "Error", message: "Dont leave any of the spaces blank , they all must be filled up , try again ! ", preferredStyle: .alert)
            alert.addAction(UIAlertAction(title: "Ok", style: UIAlertActionStyle.default, handler: nil))
            self.present(alert, animated: true, completion: nil)
        }

当我运行该项目时，它说db_connect.login(email: email!, password: passw0rd!) 的值不是空的，但它不会打印出来。 （但是，在我的 db_conn calss 中，我可以轻松地打印 responseString 并以 String 格式获得返回的 JSON。 知道我在哪里犯错了吗？我怎么可能修复它？

Answer 1

使用URLSession 发出网络请求是异步运行的，这意味着iOS 将其置于后台线程并在下载完成之前立即继续当前线程。因此，当你return result 时，它仍然是一个空字符串。您可能想要做的是将完成闭包传递给您的 login 方法，并在下载完成时使用相关数据调用它