Adding Mask to a TextField

UITextField+MaskPattern.swift

//
//  UITextField+MaskPattern.swift
//  MaskedTextField
//
//  Created by dede.exe on 10/07/16.
//
//  It's totally base on article : "http://vojtastavik.com/2015/03/29/real-time-formatting-in-uitextfield-swift-basics/"
//  And I don't mind if the original author allow me to publish it :)... But I'll keep the reference
//  I modified the original implementation to keep it as an Extension...
//

extension UITextField {
    
    private struct FKFieldPatterns {
        static var pattern          = "pattern"
        static var replacementChar  = "replacementChar"
        static var allowNumbers     = "allowNumbers"
        static var allowText        = "allowText"
    }
    
    private var pattern : String {
        if let result = objc_getAssociatedObject(self, &FKFieldPatterns.pattern) as? String {
            return result
        }
        
        return ""
    }
    
    private var replacementChar : String {
        if let result = objc_getAssociatedObject(self, &FKFieldPatterns.replacementChar) as? String {
            return result
        }
        
        return ""
    }
    
    private var allowText : Bool {
        if let result = objc_getAssociatedObject(self, &FKFieldPatterns.allowText) as? Bool {
            return result
        }
        
        return true
    }
    
    private var allowNumbers : Bool {
        if let result = objc_getAssociatedObject(self, &FKFieldPatterns.allowNumbers) as? Bool {
            return result
        }
        
        return true
    }
    
    
    func formatPattern(pattern:String?=nil, replacementChar:String?=nil,  allowText:Bool=true, allowNumbers:Bool=true)
    {
        objc_setAssociatedObject(self, &FKFieldPatterns.pattern,            pattern ?? "",         .OBJC_ASSOCIATION_RETAIN)
        objc_setAssociatedObject(self, &FKFieldPatterns.replacementChar,    replacementChar ?? "*", .OBJC_ASSOCIATION_RETAIN)
        objc_setAssociatedObject(self, &FKFieldPatterns.allowNumbers,       allowNumbers,    .OBJC_ASSOCIATION_RETAIN)
        objc_setAssociatedObject(self, &FKFieldPatterns.allowText,          allowText,       .OBJC_ASSOCIATION_RETAIN)
        registerNotifications()
    }
    
    private func registerNotifications() {
        NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(textDidChange), name: "UITextFieldTextDidChangeNotification", object: self)
    }
    
    private func removeNotifications() {
        NSNotificationCenter.defaultCenter().removeObserver(self)
    }
    
    func prepareString(string:String) -> String
    {
        var charSet : NSCharacterSet!
        
        if allowText && allowNumbers {
            charSet = NSCharacterSet.alphanumericCharacterSet().invertedSet
        }
        else if allowText {
            charSet = NSCharacterSet.letterCharacterSet().invertedSet
        }
        else if allowNumbers {
            charSet = NSCharacterSet.decimalDigitCharacterSet().invertedSet
        }
        
        let result = string.componentsSeparatedByCharactersInSet(charSet)
        return result.joinWithSeparator("")
    }
    
    func textDidChange(notification : NSNotification) {
        
        guard let text = self.text else {
            return
        }
        
        if text.characters.count > 0 && pattern.characters.count > 0
        {
            
            var finalText   = ""
            var stop        = false
            let tempString  = prepareString(text)
            
            var formatIndex = pattern.startIndex
            var tempIndex   = tempString.startIndex
            
            while !stop
            {
                let formattingPatternRange = formatIndex ..< formatIndex.advancedBy(1)
                
                if pattern.substringWithRange(formattingPatternRange) != String(replacementChar) {
                    finalText = finalText.stringByAppendingString(pattern.substringWithRange(formattingPatternRange))
                }
                else if tempString.characters.count > 0 {
                    let pureStringRange = tempIndex ..< tempIndex.advancedBy(1)
                    finalText = finalText.stringByAppendingString(tempString.substringWithRange(pureStringRange))
                    tempIndex = tempIndex.advancedBy(1)
                }
                
                formatIndex = formatIndex.advancedBy(1)
                
                if formatIndex >= pattern.endIndex || tempIndex >= tempString.endIndex {
                    stop = true
                }
                
                self.text = finalText
                
            }
        }
    }
}

//=========================================================
//=                       EXAMPLE                         =
//=========================================================
var creditCardTextField : UITextField!
var dateTextField       : UITextField!
...
cardNumberTextField.formatPattern("**** **** **** ****", replacementChar:"*", allowText: false, allowNumbers: true)
dateTextfield.formatPattern("**/**/****", replacementChar:"*", allowText:false, allowNumbers: true)

// You should move the "self.text = finalText" out of the loop. This way it will not call ui runloop to refresh the screen.
// Updated to Swift 4

// https://gist.github.com/dedeexe/13589e0a69efd228da33705fdc1415cf
// UITextField+MaskPattern.swift
// MaskedTextField
//
// Created by dede.exe on 10/07/16.
// Modified by João Paulo Serodio on 11/16/18.
//
// It's totally base on article : "http://vojtastavik.com/2015/03/29/real-time-formatting-in-uitextfield-swift-basics/"
// And I don't mind if the original author allow me to publish it :)... But I'll keep the reference
// I modified the original implementation to keep it as an Extension...
//

extension UITextField {

private struct FKFieldPatterns {
    static var pattern          = "pattern"
    static var replacementChar  = "replacementChar"
    static var allowNumbers     = "allowNumbers"
    static var allowText        = "allowText"
}

private var pattern: String {
    if let result = objc_getAssociatedObject(self, &FKFieldPatterns.pattern) as? String {
        return result
    }
    return ""
}

private var replacementChar: String {
    if let result = objc_getAssociatedObject(self, &FKFieldPatterns.replacementChar) as? String {
        return result
    }
    return ""
}

private var allowText: Bool {
    if let result = objc_getAssociatedObject(self, &FKFieldPatterns.allowText) as? Bool {
        return result
    }
    return true
}

private var allowNumbers: Bool {
    if let result = objc_getAssociatedObject(self, &FKFieldPatterns.allowNumbers) as? Bool {
        return result
    }
    return true
}

func format(pattern: String? = nil, replacementChar: String? = nil,
            allowText: Bool = true, allowNumbers: Bool = true) {

    objc_setAssociatedObject(self, &FKFieldPatterns.pattern, pattern ?? "", .OBJC_ASSOCIATION_RETAIN)
    objc_setAssociatedObject(self, &FKFieldPatterns.replacementChar, replacementChar ?? "*",
                             .OBJC_ASSOCIATION_RETAIN)
    objc_setAssociatedObject(self, &FKFieldPatterns.allowNumbers, allowNumbers, .OBJC_ASSOCIATION_RETAIN)
    objc_setAssociatedObject(self, &FKFieldPatterns.allowText, allowText, .OBJC_ASSOCIATION_RETAIN)
    registerNotifications()
}

private func registerNotifications() {
    NotificationCenter.default.addObserver(self,
                                           selector: #selector(textDidChange),
                                           name: NSNotification.Name(
                                           rawValue: "UITextFieldTextDidChangeNotification"),
                                           object: self)
}

private func removeNotifications() {
    NotificationCenter.default.removeObserver(self)
}

func prepareString(string: String) -> String {
    var charSet: CharacterSet!

    if allowText && allowNumbers {
        charSet = CharacterSet.alphanumerics.inverted
    } else if allowText {
        charSet = CharacterSet.letters.inverted
    } else if allowNumbers {
        charSet = CharacterSet.decimalDigits.inverted
    }

    let result = string.components(separatedBy: charSet)
    return result.joined(separator: "")
}

@objc func textDidChange(notification: NSNotification) {

    guard let text = self.text else {
        return
    }

    if text.count > 0 && pattern.count > 0 {
        var finalText   = ""
        var stop        = false
        let tempString  = prepareString(string: text)

        var formatIndex = pattern.startIndex
        var tempIndex   = tempString.startIndex

        while !stop {
            let formattingPatternRange = formatIndex ..< pattern.index(formatIndex, offsetBy: 1)

            if pattern[formattingPatternRange] != String(replacementChar) {
                finalText = finalText.appending(pattern[formattingPatternRange])
            } else if tempString.count > 0 {
                let pureStringRange = tempIndex ..< tempString.index(tempIndex, offsetBy: 1)
                finalText = finalText.appending(tempString[pureStringRange])
                tempIndex = tempString.index(tempIndex, offsetBy: 1)
            }

            formatIndex = pattern.index(formatIndex, offsetBy: 1)

            if formatIndex >= pattern.endIndex || tempIndex >= tempString.endIndex {
                stop = true
            }
        }
        self.text = finalText
    }
}

}