Allow only Numbers for UITextField input

Question

The iPad does not have a "Numpad" keyboard like the iPhone/iPod does.

I'm looking to find how I can restrict the user's keyboard to only accept values 0 through 9.

I would imagine using UITextField's "shouldChangeCharactersInRange" but I don't know the best way to implement it.

Answer 1

This is how you might handle the problem on a SSN verification field, you can modify the max length and remove the if statement checking for keyboard type if you need to.

There is also logic to suppress the max length alerts when the user is typing as opposed to pasting data.

Within the context of this code, presentAlert()/presentAlert: is just some basic function that presents a UIAlertController (or a legacy UIAlertView) using the message string passed.

Swift 5

// NOTE: This code assumes you have set the UITextField(s)'s delegate property to the  // object that will contain this code, because otherwise it would never be called. // // There are also some better stylistic approaches in Swift to avoid all the  // nested statements, but I wanted to keep the styles similar to allow others  // to contrast and compare between the two languages a little easier.  func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {      // Handle backspace/delete     guard !string.isEmpty else {          // Backspace detected, allow text change, no need to process the text any further         return true     }      // Input Validation     // Prevent invalid character input, if keyboard is numberpad     if textField.keyboardType == .numberPad {          // Check for invalid input characters         if CharacterSet(charactersIn: "0123456789").isSuperset(of: CharacterSet(charactersIn: string)) {              // Present alert so the user knows what went wrong             presentAlert("This field accepts only numeric entries.")              // Invalid characters detected, disallow text change             return false         }     }      // Length Processing     // Need to convert the NSRange to a Swift-appropriate type     if let text = textField.text, let range = Range(range, in: text) {          let proposedText = text.replacingCharacters(in: range, with: string)          // Check proposed text length does not exceed max character count         guard proposedText.count <= maxCharacters else {              // Present alert if pasting text             // easy: pasted data has a length greater than 1; who copy/pastes one character?             if string.count > 1 {                  // Pasting text, present alert so the user knows what went wrong                 presentAlert("Paste failed: Maximum character count exceeded.")             }              // Character count exceeded, disallow text change             return false         }          // Only enable the OK/submit button if they have entered all numbers for the last four         // of their SSN (prevents early submissions/trips to authentication server, etc)         answerButton.isEnabled = (proposedText.count == 4)     }      // Allow text change     return true } 

Objective-C

// NOTE: This code assumes you have set the UITextField(s)'s delegate property to the  // object that will contain this code, because otherwise it would never be called.  - (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {     // Handle backspace/delete     if (!string.length)     {         // Backspace detected, allow text change, no need to process the text any further         return YES;     }      // Input Validation     // Prevent invalid character input, if keyboard is numberpad     if (textField.keyboardType == UIKeyboardTypeNumberPad)     {         if ([string rangeOfCharacterFromSet:[NSCharacterSet decimalDigitCharacterSet].invertedSet].location != NSNotFound)         {             [self presentAlert: @"This field accepts only numeric entries."];             return NO;         }     }      // Length Validation     NSString *proposedText = [textField.text stringByReplacingCharactersInRange:range withString:string];      // Check proposed text length does not exceed max character count     if (proposedText.length > maxCharacters)     {         // Present alert if pasting text         // easy: pasted data has a length greater than 1; who copy/pastes one character?         if (string.length > 1)         {             // Pasting text, present alert so the user knows what went wrong             [self presentAlert: @"Paste failed: Maximum character count exceeded."];         }          // Character count exceeded, disallow text change         return NO;     }      // Only enable the OK/submit button if they have entered all numbers for the last four     // of their SSN (prevents early submissions/trips to authentication server, etc)     self.answerButton.enabled = (proposedText.length == maxCharacters);      // Allow text change     return YES; }