class ViewController: UIViewController {
  
  @IBOutlet weak var emailTextField: TKFormTextField!

  override func viewDidLoad() {
    super.viewDidLoad()

    // UITextField traditional properties
    self.emailTextField.placeholder = "Email"
    self.emailTextField.enablesReturnKeyAutomatically = true
    self.emailTextField.returnKeyType = .next
    self.emailTextField.clearButtonMode = .whileEditing
    self.emailTextField.placeholderFont = UIFont.systemFont(ofSize: 18)
    self.emailTextField.font = UIFont.systemFont(ofSize: 18)

    // TKFormTextField properties: floating placeholder title
    self.emailTextField.titleLabel.font = UIFont.systemFont(ofSize: 18)
    self.emailTextField.titleColor = UIColor.lightGray
    self.emailTextField.selectedTitleColor = UIColor.gray

    // TKFormTextField properties: underline
    self.emailTextField.lineColor = UIColor.gray
    self.emailTextField.selectedLineColor = UIColor.black
    
    // TKFormTextField properties: bottom error label
    self.emailTextField.errorLabel.font = UIFont.systemFont(ofSize: 18)
    self.emailTextField.errorColor = UIColor.red // this color is also used for the underline on error state

    // TKFormTextField properties: update error message
    // NOTE: Ideally you should show error on .editingDidEnd, and attempt to hide it on .editingChanged.
    // See the demo project on how I design the validation flow.
    self.emailTextField.addTarget(self, action: #selector(updateError), for: .editingChanged)
  }

  func updateError(textField: TKFormTextField) {
    guard let text = textField.text, !text.isEmpty else {
      textField.error = "Text is empty!" // to show error message in errorLabel
      return
    }
    textField.error = nil // to remove the error message
  }
}