为什么我在这段代码中得到“只能声明实例方法@IBAction”？答案

【问题标题】：Why am I getting "Only instance methods can be declared @IBAction" in this code?为什么我在这段代码中得到“只能声明实例方法@IBAction”？
【发布时间】：2019-07-02 15:54:39
【问题描述】：

我正在尝试为一个学校项目构建一个适用于 ios 的社交网络应用程序。我的@IBAction 登录功能不起作用，我不知道为什么。我得到的错误是：“只能声明实例方法@IBAction”

这是我的代码：

class ViewController: UIViewController {
    @IBOutlet weak var emailField: UITextField!
    @IBOutlet weak var passwordField: UITextField!`

    var userUid: String!

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
    }

    override func viewDidAppear(_ animated: Bool){
        if let _ = KeychainWrapper.standard.string(forKey: "uid") {
            performSegue(withIdentifier: "Messages", sender: nil)
        }

        func prepare(for segue: UIStoryboardSegue, sender: Any?) {

            if segue.identifier == "SignUp" {

                if let destination = segue.destination as? SignUpVC {
                    if self.userUid != nil{
                        destination.userUid = userUid
                    }
                    if self.emailField.text != nil {
                        destination.emailField = emailField.text
                    }
                    if self.passwordField.text != nil {
                        destination.passwordField = passwordField.text
                    }
                }
            }
        }

        @IBAction func SignIn (_ sender: AnyObject) {
        if let email = emailField.text, let password = passwordField.text{
            Auth.auth().signIn(withEmail: email, password: password, completion:{
                (user, error) in
                if error == nil{
                    self.userUid = user?.user.uid
                    KeychainWrapper.standard.set(self.userUid, forKey: "uid")
                    self.performSegue(withIdentifier: "Messages", sender: nil)
                } else {
                    self.performSegue(withIdentifier: "SignUp", sender: nil)
                }
            })
        }
    }
}
}

【问题讨论】：

为什么你的func prepare(for segue: UIStoryboardSegue, sender: Any?)方法在viewWillAppear里面？那要么是错误的复制/粘贴到此处，要么您需要将其移出。看起来您的 IBAction 也可能在另一个方法中，或者您已经在某处声明了一个静态方法。请整理一下这段代码，它很难阅读，显然会导致问题。
您的错误在于范围。 swift中的函数不能包含其他函数。
函数可以包含函数，但是将 prepare: 放入 viewDidLoad: 是不正确的。

标签： ios swift social-media

【解决方案1】：

func prepare(for segue: UIStoryboardSegue, sender: Any?) {

            if segue.identifier == "SignUp" {

                if let destination = segue.destination as? SignUpVC {
                    if self.userUid != nil{
                        destination.userUid = userUid
                    }
                    if self.emailField.text != nil {
                        destination.emailField = emailField.text
                    }
                    if self.passwordField.text != nil {
                        destination.passwordField = passwordField.text
                    }
                }
            }
        }

        @IBAction func SignIn (_ sender: AnyObject) {
        if let email = emailField.text, let password = passwordField.text{
            Auth.auth().signIn(withEmail: email, password: password, completion:{
                (user, error) in
                if error == nil{
                    self.userUid = user?.user.uid
                    KeychainWrapper.standard.set(self.userUid, forKey: "uid")
                    self.performSegue(withIdentifier: "Messages", sender: nil)
                } else {
                    self.performSegue(withIdentifier: "SignUp", sender: nil)
                }
            })
        }

应该在viewDidAppear之外

【讨论】：

【解决方案2】：

你为 segue 做准备，登录函数都嵌套在 viewDidAppear 方法中。使用 cmets 有助于直观地分解函数。

class ViewController: UIViewController {
    // MARK: Outlets
    @IBOutlet weak var emailField: UITextField!
    @IBOutlet weak var passwordField: UITextField!`
    // MARK: Properties
    var userUid: String!
    // MARK: Lifecycle
    override func viewDidAppear(_ animated: Bool) {
        if let _ = KeychainWrapper.standard.string(forKey: "uid") {
            performSegue(withIdentifier: "Messages", sender: nil)
        }
    }
    // MARK: Navigation
    func prepare(for segue: UIStoryboardSegue, sender: Any?) {

        if segue.identifier == "SignUp" {

            if let destination = segue.destination as? SignUpVC {
                if self.userUid != nil{
                    destination.userUid = userUid
                }
                if self.emailField.text != nil {
                    destination.emailField = emailField.text
                }
                if self.passwordField.text != nil {
                    destination.passwordField = passwordField.text
                }
            }
        }
    }
    // MARK: Actions
    @IBAction func SignIn (_ sender: AnyObject) {
        if let email = emailField.text, let password = passwordField.text{
            Auth.auth().signIn(withEmail: email, password: password, completion:{
                (user, error) in
                if error == nil{
                    self.userUid = user?.user.uid
                    KeychainWrapper.standard.set(self.userUid, forKey: "uid")
                    self.performSegue(withIdentifier: "Messages", sender: nil)
                } else {
                    self.performSegue(withIdentifier: "SignUp", sender: nil)
                }
            })
        }
    }
}

【讨论】：

【解决方案3】：

原因是您的SignIn 不是实例方法，它是viewDidAppear 内部的嵌套函数。在viewDidAppear 中添加另一个右括号

override func viewDidAppear(_ animated: Bool){
    if let _ = KeychainWrapper.standard.string(forKey: "uid") {
        performSegue(withIdentifier: "Messages", sender: nil)
    }
}

并在文件末尾删除一个

【讨论】：

【解决方案4】：

函数func prepare(for segue: UIStoryboardSegue, sender: Any?)应该在类范围内而不是嵌套在viewDidAppear中

override func viewDidAppear(_ animated: Bool){
    super.viewDidAppear(animated)
    if let _ = KeychainWrapper.standard.string(forKey: "uid"){
        performSegue(withIdentifier: "Messages", sender: nil)
    } 
}

@IBAction func SignIn (_ sender: AnyObject) {
    if let email = emailField.text, let password = passwordField.text{
        Auth.auth().signIn(withEmail: email, password: password, completion:{
            (user, error) in
            if error == nil{
                self.userUid = user?.user.uid
                KeychainWrapper.standard.set(self.userUid, forKey: "uid")
                self.performSegue(withIdentifier: "Messages", sender: nil)
            } else {
                self.performSegue(withIdentifier: "SignUp", sender: nil)
            }
        })
    }
} 
func prepare(for segue: UIStoryboardSegue, sender: Any?){ 
    if segue.identifier == "SignUp"{ 
        if let destination = segue.destination as? SignUpVC { 
            if self.userUid != nil {
                destination.userUid = userUid
            }  
            destination.emailField = emailField.text 
            destination.passwordField = passwordField.text 
        }
    } 
}

【讨论】：