Set the maximum character length of a UITextField in iOS

#define MAX_LENGTH 20

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
    if (textField.text.length >= MAX_LENGTH && range.length == 0)
    {
     return NO; // return NO to not change text
    }
    else
    {return YES;}
}