Question

我的应用中有以下网址发布请求，该请求能够获得有效的响应。但是，当我比较输入的原始字符串以响应var时，“ postResponse”为nil，即使我可以在先前的打印中看到它具有值。 Xcode 10.2.1 Swift 5

在do块中，打印命令显示从服务器返回的有关postResponse和postMessage的正确信息。这些命令在这里可以正常打印，但是在do块完成之后，随后的打印语句或对变量的任何比较都说它们为nil。

理想情况下，我希望能够将输入的内容与返回的内容进行比较，并继续执行相应的操作，但是现在最后一个代码块警报功能始终会被触发，因为postResponse在执行到该点时为零。

我在这里想念什么？

@IBAction func LoginBtn(_ sender: Any) {

    //created NSURL
    let requestURL = NSURL(string: URL_SERVICE)

    //creating NSMutableURLRequest
    let request = NSMutableURLRequest(url: requestURL! as URL)

    //setting the method to post
    request.httpMethod = "POST"

    //getting values from text fields
    let mode = "login"
    let userid = EmployeeID.text

    var postResponse : String?
    var postMessage : String?


    //creating the post parameter by concatenating the keys and values from text field
    let postParameters = "mode="+mode+"&userid="+userid!;


    //adding the parameters to request body
    request.httpBody = postParameters.data(using: String.Encoding.utf8, allowLossyConversion: false)

    //creating a task to send the post request
    let task = URLSession.shared.dataTask(with: request as URLRequest){
        data, response, error in

        if error != nil{
            print("error is \(String(describing: error))")
            return;
        }

        //parsing the response
        do {
            //converting resonse to NSDictionary
            let myJSON =  try JSONSerialization.jsonObject(with: data!, options: .mutableContainers) as? NSDictionary
            //parsing the json
            if let parseJSON = myJSON {
                //getting the json response
                postResponse = (parseJSON["AppID"] as! String)
                postMessage = (parseJSON["message"] as! String)
                //username = parseJSON["username"] as! String?
                print(postMessage!)
                print(postResponse!)

            }
        } catch {
            print(error)
        }
    }

    task.resume()

    print("userid \(String(describing: userid)) resp \(String(describing: postResponse))")

    if userid != postResponse { 
        EmployeeID.text = ""
        let alertController = UIAlertController(title: "Unrecognized EmployeeID \(login ?? "nada")", message: "Please re-type EmployeeID", preferredStyle: .alert)
        let defaultAction = UIAlertAction(title: "OK", style: .cancel, handler: nil)
        alertController.addAction(defaultAction)
        self.present(alertController, animated: true, completion: nil)
    }else{

    }

}

Answer 1

postMessage块完成后，postResponse和do在代码中为零的原因是，do块中的代码尚未执行，因此，尚未设置其值。 do块是异步调用的完成处理程序的一部分。

如何设置Swift变量，使其具有适当的范围

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