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

return [self validateNumber:string];

}

- (BOOL)validateNumber:(NSString*)number {

BOOL res = YES;

NSCharacterSet* tmpSet = [NSCharacterSet characterSetWithCharactersInString:@"0123456789"];

int i = 0;

while (i < number.length) {

NSString * string = [number substringWithRange:NSMakeRange(i, 1)];

NSRange range = [string rangeOfCharacterFromSet:tmpSet];

if (range.length == 0) {

res = NO;

break;

}

i++;

}

return res;

}