Question

我目前正在努力解决当我的segue被触发时，下一个ViewController上的内容消失或需要一段时间才能加载的问题。

这是我触发segue的代码：

                                userCount = count
                            if userCount != -1{
                                self.performSegue(withIdentifier: "GoToWelcome", sender: self)
                            }
                            if userCount == -1{
                                self.LoadSign.isHidden = true
                                self.createAlert(title: "Error!", message: "Incorrect E-Mail, Please try again")

                            }

这是两个视图控制器的屏幕截图，当按下“登录”按钮时，数据在数据库中被检查，如果它是正确的，则会触发segue： IMAGE

我的WelcomeViewController代码（尚未编辑）：

import UIKit

class WelcomeViewController: UIViewController {



@IBOutlet weak var welcomeMessage: UILabel!


override func viewDidLoad() {
    super.viewDidLoad()


}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()

}

}

这是我的LoginViewController的代码（我知道这很乱）

import UIKit

class LoginScreenController: UIViewController, UITextFieldDelegate {


@IBOutlet weak var LoadSign: UIActivityIndicatorView!
@IBOutlet weak var EMail: UITextField!
@IBOutlet var LoginScreenView: UIView!
@IBAction func LoginButton(_ sender: UIButton) {
            LoadSign.isHidden = false
            let email = EMail.text
            let SQLurl = URL(string:"[myUrl]")

            let task = URLSession.shared.dataTask(with: SQLurl!) { (data, responce, error) in
                if error != nil
                {
                    print("error")

                }
                else
                {
                    if let content = data
                    {
                        do
                        {
                            let myJson = try JSONSerialization.jsonObject(with: content, options: JSONSerialization.ReadingOptions.mutableContainers) as! NSArray


                            var notInDB = false
                            var count = 0
                            var myJsonCount = myJson[count] as! NSDictionary
                            var EmailCount = (myJsonCount["txtEmailAddress"]) as! NSString
                            var userCount = 0






                            while email != EmailCount as String && notInDB == false{
                                count = count+1
                                myJsonCount = myJson[count] as! NSDictionary
                                EmailCount = (myJsonCount["txtEmailAddress"]) as! NSString
                                if count == (myJson.count-1){
                                    print("Error! E-Mail not found in database")
                                    notInDB = true
                                    count = -1


                                }
                            }

                            userCount = count
                            if userCount != -1{
                                self.performSegue(withIdentifier: "GoToWelcome", sender: nil)
                            }
                            if userCount == -1{
                                self.LoadSign.isHidden = true
                                self.createAlert(title: "Error!", message: "Incorrect E-Mail, Please try again")

                            }




                        }
                        catch
                        {

                        }
                    }
                }
            }
            task.resume()


}




override func viewDidLoad() {
    super.viewDidLoad()
    EMail.delegate = self
    EMail.adjustsFontSizeToFitWidth = true



}

func textFieldShouldReturn(_ textField: UITextField) -> Bool {
    textField.resignFirstResponder()
    return true
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()

}

func createAlert (title: String, message: String)
{
    let alert = UIAlertController(title: title, message: message, preferredStyle: UIAlertControllerStyle.alert)
    alert.addAction(UIAlertAction(title: "Try Again", style: UIAlertActionStyle.default, handler: { (action) in
        alert.dismiss(animated: true, completion: nil)

    }))
    self.present(alert, animated: true, completion: nil)
}

}

有什么理由说明会发生这种情况吗？谢谢！

Answer 1

我认为问题可能是您从不同的线程使用UIKit。 UIKit调用performSegue（可能是self.createAlert调用的内容，虽然我从你给出的代码中无法知道）应该只从主线程中调用。

我的建议是在dataTask的完成处理程序中处理与您的请求相关的内容，然后将控制权传递回主线程以处理其余部分。这是基于您发送的代码的草图。请注意，我们只是获取响应数据并在dataTask的后台线程中解析JSON，然后将控制传递给主线程上的函数来完成剩下的工作：

@IBAction func LoginButton(_ sender: UIButton) {
            LoadSign.isHidden = false
            let email = EMail.text
            let SQLurl = URL(string:"[myUrl]")

            let task = URLSession.shared.dataTask(with: SQLurl!) { (data, responce, error) in
                if error != nil
                {
                    print("error")

                }
                else
                {
                    do {
                    // parse the JSON
                    if let myJson = try JSONSerialization.jsonObject(with: content, options: JSONSerialization.ReadingOptions.mutableContainers) as? NSArray {
                        DispatchQueue.main.async { self.handleLoginData(myJson) }
                    } catch {
                        print("JSON Parse error")
                    }
                }
            }
            task.resume()

}

func handleLoginData(myJson: NSArray) {
    do {
        var notInDB = false
        var count = 0
        var myJsonCount = myJson[count] as! NSDictionary
        var EmailCount = (myJsonCount["txtEmailAddress"]) as! NSString
        var userCount = 0

        while email != EmailCount as String && notInDB == false {
            count = count+1
            myJsonCount = myJson[count] as! NSDictionary
            EmailCount = (myJsonCount["txtEmailAddress"]) as! NSString
            if count == (myJson.count-1) {
                print("Error! E-Mail not found in database")
                notInDB = true
                count = -1
            }
        }

        userCount = count
        if userCount != -1 {
            self.performSegue(withIdentifier: "GoToWelcome", sender: nil)
        } else {
            self.LoadSign.isHidden = true
            self.createAlert(title: "Error!", message: "Incorrect E-Mail, Please try again")
        }
    }
    catch
    {

    }
}

我必须稍微使用代码来使其工作，但请注意它如何通过请求将请求的数据处理留下，并将问题域的工作分离到另一个函数。使用异步块时，尝试将任何特定块中的所有工作完成，只与一个任务相关。

从视图控制器触发segue不会正确加载下一个ViewController上的内容

1 个答案: