Validate textfield for number input

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {

    static NSCharacterSet *charSet = nil;

    if(!charSet) {

        charSet = [[[NSCharacterSet characterSetWithCharactersInString:@"0123456789."] invertedSet] retain];

    }

    NSRange location = [string rangeOfCharacterFromSet:charSet];

    return (location.location == NSNotFound);

}