Uppercase characters in UItextfield

Set your textfield type autocapitalizationType to UITextAutocapitalizationTypeAllCharacters on the UITextField

self.yourTexField.autocapitalizationType = UITextAutocapitalizationTypeAllCharacters;

After call delegate

// delegate method

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
    NSRange lowercaseCharRange = [string rangeOfCharacterFromSet:[NSCharacterSet lowercaseLetterCharacterSet]];

    if (lowercaseCharRange.location != NSNotFound) {
        textField.text = [textField.text stringByReplacingCharactersInRange:range
                                                                 withString:[string uppercaseString]];
        return NO;
    }

    return YES;
}

Swift 5.4.2

       self.yourTextField.autocapitalizationType = .allCharacters