class ViewController: UIViewController, UITextFieldDelegate {
 @IBOutlet weak var textField1: UITextField!
 @IBOutlet weak var textField1: UITextField!

textField1.tag = 1
   textField2.tag = 2

   textField1.delegate = self
   textField1.returnKeyType = .Done
   textField2.delegate = self
   textField2.returnKeyType = .Done

func textFieldShouldReturn(textField: UITextField) -> Bool {
　  switch (textField.tag) {
    case 1:
        textField.resignFirstResponder()
        break
    case 2:
        textField.resignFirstResponder()
        break
    }
    return true

NSNotificationCenter.defaultCenter().addObserver(self,selector: "textFieldDidChange:",name: UITextFieldTextDidChangeNotification, object: nil)

  func textFieldDidChange(_ textField:UITextField, notification: NSNotification) {
    var maxLength: Int = 0
    switch (textField.tag) {
    case 1:
        maxLength = 10
        break
    case 2:
        maxLength = 5
        break
    }

    let textField = notification.object as! UITextField

    if let text = textField.text {
      if textField.markedTextRange == nil && text.characters.count > maxLength {
        textField.text = text.substring(to: text.index(text.startIndex, offsetBy: maxLength))
}