如何延迟异步函数并等待完成块执行？ [复制]

Question

我有这个函数，它有一个完成块，函数异步返回而不等待完成。

我希望我的函数延迟它的返回，直到它的完成块完成。我更改了回调函数，但它不起作用，我是 swift 新手，所以对 GCD 知之甚少，他们的 API 也发生了很大变化。

 func authenticateCredentials(usernameString: String, passwordString: String, completion: @escaping (Bool)-> Void)  {


            var boolVal: Bool = false
            client.invokeAPI("AuthenticateAndFetchData",
                             body: nil,
                             httpMethod: "GET",
                             parameters: ["userid": usernameString,"password":passwordString],
                             headers: nil)
            {
                (result, response, error) -> Void in
                if let err = error {
                    print("ERROR ", err)

                } else if let res = result {
                    let jsonArray = res as! NSArray
                    // print(jsonArray)
                    for value in jsonArray[0] as! NSDictionary {
                        let jsonstring = value.value as! String
                        NetworkService.jsonResponse = jsonstring
                        if let data = jsonstring.data(using: .utf8) {
                            if let content = try? JSONSerialization.jsonObject(with: data, options: []),
                                let array = content as? [[String: Any]]
                            {
                                for jsondict in array {

                                    let auth = jsondict["IsAuth"]! as! String
                                    print(type(of: auth))
                                    print(auth)
                                    boolVal = (auth == "true") ? true : false
                                    self.isAuth = boolVal
                                    print(boolVal)

                                    completion(boolVal) // callback here
                                }
                            }
                        }
                    }

                }
            }

      }

我在这样的登录操作中从我的 viewController 调用这个函数。

 // After login button is pressed
    @IBAction func loginButtonTapped(_ sender: UIButton) {

        let userid = userIDtxt.text
        let password = userpasswordtxt.text
        //Display an alert if no text is entered 
        if (userid?.isEmpty)! || (password?.isEmpty)! {
            displayAlertMessage("Please enter userid/password")
        }
            // take this userid and password and authenticate from sql server and move to 

        else {
            // Run the spinner to show the task is in progress
            print("\(userid)" + " " + "\(password)")
            nw.authenticateCredentials(usernameString: userid!, passwordString: password!){
                (boolVal) in

                    self.nw.isAuth = boolVal


            }

            showActivityIndicatory(uiview: view)

            if nw.isAuth == true {


            // User authenticated

            }
            else {

            // wrong user
            }

        }


    }

所以这里authenticateCredentials函数预先返回，它返回false，所以当我第一次点击我的登录按钮时，我收到false，当我第二次点击它时，我收到true。我想在第一次点击时接收真实和认证的用户。

Answer 1

这应该可以 - 回调后更新你的 UI

nw.authenticateCredentials(usernameString: userid!, passwordString: password!){ [weak self] (boolVal) in
        guard let `self` = self else {
             return
        } //to avoid memory leak
        self.nw.isAuth = boolVal

        showActivityIndicatory(uiview: view)

        if nw.isAuth == true {


            let userData = User.getUserData()
            print("FirstName: \(userData.LastName)")
            showActivityIndicatory(uiview: view)

            displayAlertMessage("User authenticated.")
            hideActivityIndicator(uiView: view)
            self.saveData(userData: userData)

            print("Welcome123 \(userid)")

        }
        else {

            displayAlertMessage("Wrong Username/Password. Please try again.")
            hideActivityIndicator(uiView: view)
        }
    }

基本思路：

func asyncA(handlerA: () -> ()) {
   asyncB({
       handlerA()
   })
}

func asyncB(handlerB: () -> ()) {
    handlerB()
}

func uiviewcontrollerfunc() {
    asyncA({ [weak self] in
       //update ui
  })
}