How to customize numeric input for a UITextField?

Question

I have a UITextField (that represents a tip value) in my Storyboard that starts out as $0.00. If the user types an 8, I want the textField to read $0.08. If the user then types a 3, I want the textField to read $0.83. If the user then types 5, I want the textField to read $8.35. How would I go about changing the input to a UITextField in this manner?

Answer 1

You can do this with the following four steps:

1. Make your viewController a UITextFieldDelegate by adding that to the class definition.
2. Add an IBOutlet to your textField by Control-dragging from the UITextField in your Storyboard to your code. Call it myTextField.
3. In viewDidLoad(), set your viewController as the textField’s delegate.

4. Implement textField:shouldChangeCharactersInRange:replacementString:. Take the incoming character and add it to the tip, and then use the String(format:) constructor to format your string.

   import UIKit
   
   class ViewController: UIViewController, UITextFieldDelegate {
   
       @IBOutlet weak var myTextField: UITextField!
   
       // Tip value in cents
       var tip: Int = 0
   
       override func viewDidLoad() {
           super.viewDidLoad()
           myTextField.delegate = self
           myTextField.text = "$0.00"
       }
   
       func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool {
           if let digit = Int(string) {
               tip = tip * 10 + digit
               textField.text = String(format:"$%d.%02d", tip/100, tip%100)
           }
           return false
       }
   }