快速聚焦文本字段

我在注册屏幕上有 4 个文本字段，我将其设置为当用户在每个文本字段上按“下一步”时，下一个文本字段将获得焦点。代码如下：

func textFieldShouldReturn(textField: UITextField) -> Bool {
    if (textField == self.fNameField) {
        textField.resignFirstResponder()
        self.sNameField.becomeFirstResponder()
    }
    else if (textField == self.sNameField) {
        self.emailField.becomeFirstResponder()
        
    } else if (textField == self.emailField) {
        self.passwordField.becomeFirstResponder()
    }
    else {
        var thereWereErrors = checkForErrors()
        if !thereWereErrors
        {
            //conditionally segue to next screen
        }
    }
    
    return true
}

在返回最终文本字段时，我调用错误检查函数（如下）。在其中，如果任何字段存在问题，我想集中该文本字段，以便用户可以轻松更正它。发生的情况是，有错误的文本字段聚焦（按照 checkForErrors 函数的指示）一秒钟，但随后焦点切换回密码文本字段。我也尝试添加self.passwordField.resignFirstResponder()进入上述函数的最后一个 else ，这使得密码字段失去焦点，但遇到问题的文本字段根本没有获得焦点（甚至没有像以前那样一秒钟）我该如何解决这个问题？

func checkForErrors() -> Bool
{
    var errors = false
    let title = "Error"
    var message = ""
    if fNameField.text.isEmpty {
        errors = true
        message += "First name empty"
        alertWithTitle(title, message: message, ViewController: self)
        self.fNameField.becomeFirstResponder()
    }
    else if sNameField.text.isEmpty
    {
        errors = true
        message += "Surname empty"
        alertWithTitle(title, message: message, ViewController: self)
        self.sNameField.becomeFirstResponder()
    }
    else if emailField.text.isEmpty
    {
        errors = true
        message += "Email empty"
        alertWithTitle(title, message: message, ViewController: self)
        self.emailField.becomeFirstResponder()
    }
    else if !isValidEmail(emailField.text)
    {
        errors = true
        message += "Invalid Email Address"
        alertWithTitle(title, message: message, ViewController: self)
        self.emailField.becomeFirstResponder()
    }
    else if passwordField.text.isEmpty
    {
        errors = true
        message += "Password empty"
        alertWithTitle(title, message: message, ViewController: self)
        self.passwordField.becomeFirstResponder()
    }
    else if count(passwordField.text.utf16)<8
    {
        errors = true
        message += "Password must be at least 8 characters"
        alertWithTitle(title, message: message, ViewController: self)
        self.passwordField.becomeFirstResponder()
    }
    
    return errors
}

注意我已经包含了 textField 委托。

根据要求带有标题功能的警报：

func alertWithTitle(title: String!, #message: String, #ViewController: UIViewController) {
    let alert = UIAlertController(title: title, message: message, preferredStyle: .Alert)
    let action = UIAlertAction(title: "OK", style: .Cancel, handler: nil)
    alert.addAction(action)
    ViewController.presentViewController(alert, animated: true, completion: nil)
}

theTextFieldYouWant.becomeFirstResponder()