ios 身份证号输入判断

#pragma mark -监听uitextfield的值得变化
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
    if (textField == self.shenFenZhengTF) {
        if (range.length == 1 && string.length == 0) {
            return YES;
        }else if (self.shenFenZhengTF.text.length >= 18) {
            self.shenFenZhengTF.text = [textField.text substringToIndex:18];
            //email
            [self showAlertInfor:@"身份证号最多输入18位"];
            return NO;
        }
        if (self.shenFenZhengTF) {
            NSMutableString *str = [NSMutableString stringWithFormat:@"%@",textField.text];
            [str replaceCharactersInRange:range withString:string];
            NSString *regex = @"[A-Za-z0-9]{0,18}";
            NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF MATCHES %@", regex];
            BOOL isValid = [predicate evaluateWithObject:str];
            return isValid;
        }
    }
}