限制textfield只能输入数字

// 需要使用的textfield遵循代理- (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;}