Essential Books

UITextField - Restrict textfield to certain characters

suggest change

If you want to perform a user input validation of your textfield use the following code snippet: 

// MARK: - UITextFieldDelegate

let allowedCharacters = CharacterSet(charactersIn:"0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvxyz").inverted    

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    
    let components = string.components(separatedBy: allowedCharacters)
    let filtered = components.joined(separator: "")
    
    if string == filtered {
        
        return true

    } else {
        
        return false
    }
}

Objective-C 

#define ACCEPTABLE_CHARACTERS @"0123456789 ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string  
{
      NSCharacterSet *cs = [[NSCharacterSet characterSetWithCharactersInString:ACCEPTABLE_CHARACTERS] invertedSet];

      NSString *filtered = [[string componentsSeparatedByCharactersInSet:cs] componentsJoinedByString:@""];

      return [string isEqualToString:filtered];
}

In addition you can also use character sets provided by apple to perform validation:

Take a look at https://developer.apple.com/reference/foundation/nscharacterset 

let allowedCharacters = CharacterSet.alphanumerics.inverted
let allowedCharacters = CharacterSet.capitalizedLetters.inverted
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UITextField Delegate:
* UITextField - Restrict textfield to certain characters
* Actions when a user has started / ended interacting with a textfield
* 03Find Next Tag Manage Keyboard
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