尝试在两个Xml文档之间进行联接时出现NullReferenceException

Question

I have an Xml document that looks something like this (It contains more parents and children that the shown):

<item cid="0x12e3">
    <item cid="0x1310">
        <item cid="0x158b">
            <item luid="2001"/>
            <item luid="2002"/>
        </item>
        <item cid="0x13313">
            <item luid="2001"/>
            <item luid="2002"/>
        </item>
        ... 
    </item>
</item>

and Also I have an Xml document with some properties like this:

<?xml version="1.0" encoding="UTF-8"?>
<EditorRule>
     <Properties>
         <Property name="Comment" luid="2001"/>
         ...
     </Properties>
</EditorRule>

Now, I'm doing a Join between the two files to Select the XElements from the first xml that are found on the Second xml :

(from element in Element.Elements().Elements().Elements()
            join property in propertiesFromFile on element.Attribute("luid").Value equals property.Luid 
            select new IpjItem(element));

This works fine, and when I Iterate over this IEnumerable it prints the Name="Comment" and so on.

My problem is that it only works for the first XElement. So, going back to the first Xml . It only prints the Children from the Node with cid = 0x158b . After its done with that Element it throws the NullReferenceException and does not go to to the one with the cid = 0x13313 . Why is this happening?

Thanks!

Answer 1

Yes. As @Selman22 alarmly inferred, my problem was in Element.Elements() . Also I added a better Where clause to check if the attribute existed.

return (from element in Element.Elements()
            where element.Attribute("luid") != null
            join property in RuleEditorXml.Properties on element.Attribute("luid").Value equals property.Luid
            select new IpjItem(element, Parent));