CODEWITHSUNDEEP
c#.net
Gerald Oakham
Gerald Oakham

Reputation: 173

c# "if" statement not working . Checking all variables are null

I have this XML file

<?xml version="1.0" encoding="utf-8"?>
<message>
 <success/>
  <bookings>
   <booking>
     <rooms>
      <room roomCode ="101" uniqueId="abc">
      <stays>
        <stay usedfrom="9:30" usedto="10:30" quantity="1" Price="62.5" rateCode="1"/>
      </stays>
      <extras>
        <extra from="9:30" to="10:30" unitPrice="5.5" extraCode="coffee" quantity="1" inclusive="0"/>
      </extras>
      <guests>
        <guest firstName="John" lastName="Doe" title="MR" ageRange="0"/>
      </guests>
    </room>
    <room roomCode ="Brd" uniqueId="xyz">
      <stays>
        <stay usedfrom="13:30" usedto="15:30" quantity="1" unitPrice="60.0000" rateCode="RACK"/>
      </stays>
      <guests>
        <guest firstName="Jean" lastName="Doe" title="MRS" ageRange="0"/>
      </guests>
    </room>
  </rooms>
</booking>

and i'm trying to run a check to make sure its in the correct format (ie certain elements are present). The code I have been using is 

XmlNodeList Successful = doc.GetElementsByTagName("success");
XmlNodeList Bookings = doc.GetElementsByTagName("bookings");
XmlNodeList Booking = doc.GetElementsByTagName("booking");
XmlNodeList Rooms = doc.GetElementsByTagName("rooms");

if ((Successful != null) && (Bookings != null) && (Booking != null) && (Rooms != null))
{
    //do something
}
else
{
    //do something else
}

This ALWAYS works thought.

If I change the one of the values to

XmlNodeList Rooms = doc.GetElementsByTagName("NoSuchElement");

(which does not exist in the XML) it still "works".

Can someone point out what I've done wrong (I've tried removing the outer brackets from the "if" statement, but this did not change the outcome).

Thanks

Upvotes: 0

Views: 193

Answers (2)

MakePeaceGreatAgain
MakePeaceGreatAgain

Reputation: 37000

As opf the docs:

An XmlNodeList containing a list of all matching nodes. If no nodes match name, the returned collection will be empty.

The method can´t return null, but an empty list. So check for this instead:

if(theNodeList.Any()) { ... }
else { /* error */ }

Upvotes: 4

Pac0
Pac0

Reputation: 23129

This is because oc.GetElementsByTagName("NoSuchElement"); is never null.

As per the documentation, if no element exists, it returns en empty collection which is not null.

You have to check the Count of the result.

something like : 

if (Successful.Count() != 0 && ...)

or 

if (!Successful.Any() && ... )

Upvotes: 3

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