Uneditable prefix inside a UITextField using Swift - swift

Question

I'm having a problem regarding the creation of a prefix inside a UITextField using the new Swift language. Currently I have created the UITextField using the Interface Builder and I have assigned an IBOutlet to it, named usernameField, then using the textFieldDidBeginEditing function I write a NSMutableAttributedString inside it, named usernamePrefix, containing only the word "C-TAD-" and finally I limited the UITextField max characters number to 13, like so:
class ViewController: UIViewController, UITextFieldDelegate {
#IBOutlet var usernameField : UITextField!
private var usernamePrefix = NSMutableAttributedString(string: "C-TAD-")
func textFieldDidBeginEditing(textField: UITextField) {
if textField == usernameField {
if usernameField.text == "" {
usernameField.attributedText = usernamePrefix
}
}
usernameField.addTarget(self, action: "textFieldDidChangeText:", forControlEvents:UIControlEvents.EditingChanged)
}
func textField(textField: UITextField!, shouldChangeCharactersInRange range: NSRange, replacementString string: String!) -> Bool {
let maxUsernameLength = countElements(usernameField.text!) + countElements(string!) - range.length
return maxUsernameLength <= 13
}
override func viewDidLoad() {
super.viewDidLoad()
usernameField.delegate = self
passwordField.delegate = self
}
}
Now, how can I assign new parameters to the usernamePrefix in order to have to give 2 different colors to the text written in the UITextField? I would like to have the prefix in .lightGreyColor() and the rest in .blackColor(). Also how can I make the usernamePrefix un-editable and un-deletable by the user?
Thanks for the help

Answer 1

Simpler option would be to set leftView of the UITextField and customise it how you like it:
let prefix = UILabel()
prefix.text = "C-TAD-"
// set font, color etc.
prefix.sizeToFit()
usernameField.leftView = prefix
usernameField.leftViewMode = .whileEditing // or .always
It is un-editable and un-deletable and you don't need to do any calculations to check the length of the input.

Answer 2

For the first part, you can refactor your delegate method as follow.
func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool {
//This makes the new text black.
textField.typingAttributes = [NSForegroundColorAttributeName:UIColor.blackColor()]
let protectedRange = NSMakeRange(0, 6)
let intersection = NSIntersectionRange(protectedRange, range)
if intersection.length > 0 {
return false
}
if range.location == 12 {
return true
}
if range.location + range.length > 12 {
return false
}
return true
}
This will lock down both the length at 13 and the prefix can not be deleted. Everything typed will be UIColor.blackColor()
Then you can a method like the following in your viewDidLoad, to set the prefix.
func makePrefix() {
let attributedString = NSMutableAttributedString(string: "C-TAD-")
attributedString.addAttribute(NSForegroundColorAttributeName, value: UIColor.lightGrayColor(), range: NSMakeRange(0,6))
textField.attributedText = attributedString
}

Answer 3

I've adopted the solution from Jeremy and make a little bit improvement to make it a bit more swifty, and also handle the case when user pastes multiple characters into the text field.
func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
let protectedRange = NSRange(location: 0, length: usernamePrefix.length)
let intersection = protectedRange.intersection(range)
// prevent deleting prefix
if intersection != nil {
return false
}
// limit max character count
if (textField.text ?? "").count + string.count > 13 {
return false
}
return true
}