iosipadcocoa-touchuitextfielduikeyboard

Allow only Numbers for UITextField input


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.


Solution

  • 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;
    }