How to limit NSTextField text length and keep it always upper case?

Question

Need to have an NSTextField with a text limit of 4 characters maximum and show always in upper case but can\'t figure out a good way of achieving that. I\'ve tried to do it

Answer 1

I needed a Formatter to convert to uppercase for Swift 4. For reference I've included it here:

import Foundation

class UppercaseFormatter : Formatter {

    override func string(for obj: Any?) -> String? {
        if let stringValue = obj as? String {
            return stringValue.uppercased()
        }
        return nil
    }

    override func getObjectValue(_ obj: AutoreleasingUnsafeMutablePointer?, for string: String, errorDescription error: AutoreleasingUnsafeMutablePointer?) -> Bool {
        obj?.pointee = string as AnyObject
        return true
    }
}