Xml Element not present and list null and Object r

问题:

I am retireving data from xml field, there are nodes that may not exist (because the xml file is generated dynamically) . the problem is when I look for a node and it is not present in the file , it returns a null list and this exception :"d Object reference not set to an instance of an object ". Here is the code :

public static List<Transaction> getXmlTransactions(XElement n)
        {


            var transactions = n.Elements("Transaktion").Select(p => new Transaction()
                {
                    TransID = p.Element("TransID") != null ? p.Element("TransID").Value : String.Empty,
                    TypeTransaction = p.Element("TransArt") != null ? p.Element("TransArt").Value : String.Empty,
                    DateEntree = p.Element("BuchDat") != null ? p.Element("BuchDat").Value : String.Empty,
                    Montant = p.Element("BetragWAE") != null ? p.Element("BetragWAE").Value : String.Empty,
                    Devise = p.Element("BuchDat") != null ? p.Element("Waehrung").Value : String.Empty,
                    // BanqueCorespondante = p.Element("BuchDat") != null ? p.Element("Waehrung").Value : String.Empty,   Dans le compte
                    Pays = p.Element("GegenLandText") != null ? p.Element("GegenLandText").Value : String.Empty,
                    AbreviationPays = p.Element("GegenLand") != null ? p.Element("GegenLand").Value : String.Empty,
                    autresinfo = p.Element("Kommentar") != null ? p.Element("Kommentar").Value : String.Empty
                }).ToList();


                return transactions;



        } 

 public static List<Compte> getXmlComptes(XElement n)
        {


            var comptes = n.Elements("Konto").Select(p => new Compte()
            {
                NumCompte = p.Element("KtoNr") != null ? p.Element("KtoNr").Value : String.Empty,
                typeCompte = p.Element("KontoArt") != null ? p.Element("KontoArt").Value : String.Empty,
                DateOuverture = p.Element("KtoOeff") != null ? p.Element("KtoOeff").Value : String.Empty,
                IBAN = p.Element("IBAN") != null ? p.Element("IBAN").Value : String.Empty,
                Devise = p.Element("Waehrung") != null ? p.Element("Waehrung").Value : String.Empty,
                CommentairesCompte = p.Element("Kommentar") != null ? p.Element("Kommentar").Value : String.Empty,
                Trans = getXmlTransactions(p)
            }).ToList();


                return comptes;

        }

回答1:

From code you provided I can say, that you are passing null to getXmlComptes method (or to getXmlTransactions if it is called elsewhere).

I suggest you to cast elements:

public static List<Transaction> getXmlTransactions(XElement n)
{
   if (n == null)
       throw new ArgumentNullException("Konto is null");

    var transactions = from t in n.Elements("Transaktion")
                       select new Transaction {
                           TransID = (string)t.Element("TransID"),
                           TypeTransaction = (string)t.Element("TransArt"),
                           DateEntree = (string)t.Element("BuchDat"),
                           Montant = (string)t.Element("BetragWAE"),
                           Devise = (string)t.Element("BuchDat"),
                           Pays = (string)t.Element("GegenLandText"),
                           AbreviationPays = (string)t.Element("GegenLand"),
                           autresinfo = (string)t.Element("Kommentar")
                       };

    return transactions.ToList();
}

And second method:

public static List<Compte> getXmlComptes(XElement n)
{
   if (n == null)
       throw new ArgumentNullException("Something is null");

    var comptes = from k in n.Elements("Konto")
                  select new Compte
                  {
                      NumCompte = (string)k.Element("KtoNr"),
                      typeCompte = (string)k.Element("KontoArt"),
                      DateOuverture = (string)k.Element("KtoOeff"),
                      IBAN = (string)k.Element("IBAN"),
                      Devise = (string)k.Element("Waehrung"),
                      CommentairesCompte = (string)k.Element("Kommentar"),
                      Trans = getXmlTransactions(k)
                  };

    return comptes.ToList();
}

Run this code and you'll see were you are passing null. If you need to assign empty string to some property if element is missing in xml, then use null-coalescing operator:

TypeTransaction = (string)t.Element("TransArt") ?? ""

But I would keep property value as null to show that it was not in xml.