title: How to prevent empty or whitespaces in UITextField in Swift?
body: <p>I am trying to prevent a UITextField from being entered space character or no character, but works only for no character. What I need is: the user is not allowed to save textfield without inputing any character and also just spaces; But the user can input, for example: "New Category". So spaces are only allowed between letters or number, but not only spaces.</p>
  
  <p>Here´s my code:</p>
  
  <pre><code>@IBAction func btnAddCategory(sender: AnyObject) {
      let alert = UIAlertController(title: "Ajouter une catégorie", message: nil, preferredStyle: .Alert)
      alert.view.tintColor = Utils.colorFromHex(0x585858)
      let confirmAction = UIAlertAction(title: "OK", style: .Default, handler: ({ (_) in
          if let field = alert.textFields?[0] {
              if field.text! == NSCharacterSet.whitespaceCharacterSet() || field.text! == ""{
                  self.displayAlert("Attention", alertMsg: "Vous ne pouvez pas créer des données vides")
              } else {
                  if self.checkDuplicates(field.text!) {
                      self.displayAlert("Attetion", alertMsg: "Vous avez déjà une catégorie avec ce nom !")
                  } else {
                      self.saveCategory(field.text!)
                      self.tableView.reloadData()
                  }
              }
          }
          }
      ))
  
      let cancelAction = UIAlertAction(title: "Annuler", style: .Cancel, handler: nil)
  
      alert.addTextFieldWithConfigurationHandler({(textField) in
          textField.placeholder = "Titre"
          textField.font = UIFont(name: "Roboto-Light", size: 15)!
      })
  
      alert.addAction(confirmAction)
      alert.addAction(cancelAction)
  
      self.presentViewController(alert, animated: true, completion: nil)
  }
  </code></pre>
  
  <p>So anyone could help me on this?</p>