為什么我不能在函數（Swift3）中訪問ViewController變量？

Question

這讓我發瘋。 這應該是世界上最簡單的事情，無論我嘗試什么，都行不通。

我想做的很簡單。 我的視圖中有一個文本字段和一個按鈕。 您在文本字段中輸入一個ID號，然后單擊按鈕。 當您按下按鈕時，它將執行一個Web請求，將ID號發送到PHP腳本，然后對其進行處理並返回一個字符串。 我只想將返回的字符串存儲到變量，然后通過segue將其發送到新的視圖控制器。

到目前為止，這是我的代碼：

class ViewController: UIViewController {
    //================ Member Variables ================//
    var customerDetails: NSString = ""

    //================ Object Outlets ================//
    @IBOutlet weak var deviceID: UITextField!

    //================ Object Actions ================//
    @IBAction func checkDeviceID(_ sender: UIButton) {
        print(deviceID.text!)
        validateDevice(deviceID: deviceID.text!)
    }

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        let step2VC: Step2ViewController = segue.destination as! Step2ViewController
        step2VC.deviceID = deviceID.text!
        step2VC.customerDetails = customerDetails
    }

    //================ Custom Methods ================//
    func validateDevice(deviceID: String) {
        //Send a request out to server to validate credentials
        let sessionConfig = URLSessionConfiguration.default
        let session = URLSession(configuration: sessionConfig, delegate: nil, delegateQueue: nil)
        guard let URL = URL(string: "http://monitt.dynamiscms.com/library/getCustomerDetails.php") else {return}
        let request = NSMutableURLRequest(url: URL)

        request.httpMethod = "POST"

        request.addValue("application/json; charset=utf-8", forHTTPHeaderField: "Content-Type")

        let bodyObject: [String: String] = [
            "deviceID": deviceID
        ]

        request.httpBody = try! JSONSerialization.data(withJSONObject: bodyObject, options: [])
        var responseString: NSString = ""

        let task = URLSession.shared.dataTask(with: request as URLRequest) {
            data, response, error in

            if (error == nil) {
                // Success
                let statusCode = (response as! HTTPURLResponse).statusCode
                print("URL Session Task Succeeded: HTTP \(statusCode)")

                responseString = NSString(data: data!, encoding: String.Encoding.utf8.rawValue)!
                self.customerDetails = responseString

                print("responseString = \(responseString)")
            }
            else {
                // Failure
                print("URL Session Task Failed: %@", error!.localizedDescription);
            }
        }

        task.resume()
        session.finishTasksAndInvalidate()

        performSegue(withIdentifier: "setupStep2", sender: nil)
    }
}

在我的validateDevice函數（具有打印語句）中，它成功顯示了PHP腳本返回的結果。 但是，盡管事實上我在函數外部預定義了變量，但我似乎仍然無法獲得customerDetails變量來保存腳本返回的結果。

任何人都可以對我做錯的事情有所了解嗎？

一個成功的答案是允許我將“ customerDetails”的內容設置為下一個ViewController中的文本字段，並使其包含來自Web腳本的內容。

Answer 1

網絡通話結束后，您應該執行Segue

 let task = URLSession.shared.dataTask(with: request as URLRequest) {
        data, response, error in

        if (error == nil) {
            // Success
            let statusCode = (response as! HTTPURLResponse).statusCode
            print("URL Session Task Succeeded: HTTP \(statusCode)")

            responseString = NSString(data: data!, encoding: String.Encoding.utf8.rawValue)!
            self.customerDetails = responseString
            //Here
            self.performSegue(withIdentifier: "setupStep2", sender: nil)
            print("responseString = \(responseString)")
        }
        else {
            // Failure
            print("URL Session Task Failed: %@", error!.localizedDescription);
        }
    }

    task.resume()

此外，無需致電

 session.finishTasksAndInvalidate()

Answer 2

您將使用self ，看起來就像您一樣。

您是否等到網絡通話結束后才訪問（或傳遞） customerDetails ？

將performSegue(forIdentifier:sender:)調用移至網絡調用閉包內部。 編譯器會警告您，您需要添加self 。

func validateDevice(deviceID: String) {

    //Send a request out to server to validate credentials

    let sessionConfig = URLSessionConfiguration.default
    let session = URLSession(configuration: sessionConfig, delegate: nil, delegateQueue: nil)
    guard let URL = URL(string: "http://monitt.dynamiscms.com/library/getCustomerDetails.php") else {return}
    let request = NSMutableURLRequest(url: URL)

    request.httpMethod = "POST"

    request.addValue("application/json; charset=utf-8", forHTTPHeaderField: "Content-Type")

    let bodyObject: [String: String] = [
        "deviceID": deviceID
    ]

    request.httpBody = try! JSONSerialization.data(withJSONObject: bodyObject, options: [])
    var responseString: NSString = ""

    let task = URLSession.shared.dataTask(with: request as URLRequest) {
        data, response, error in

        if (error == nil) {
            // Success
            let statusCode = (response as! HTTPURLResponse).statusCode
            print("URL Session Task Succeeded: HTTP \(statusCode)")

            responseString = NSString(data: data!, encoding: String.Encoding.utf8.rawValue)!
            self.customerDetails = responseString

            print("responseString = \(responseString)")
            self.performSegue(withIdentifier: "setupStep2", sender: nil)
        }
        else {
            // Failure
            print("URL Session Task Failed: %@", error!.localizedDescription);
        }
    }

    task.resume()
}