c# - Select multiple elements with Linq to XML -

i have c# application , need extract multiple elements linq xml collection.

i have following extract xml file

    <sns>     <uniquesystem><system>49</system><label>engines</label>         <uniquesubsystem><subsystem>30</subsystem><label>apu</label>             <uniqueunit><unit>00</unit><label>starter</label>     </uniqueunit>     </uniquesubsystem>     </uniquesystem>     <uniquesystem><system>50</system><label>hydraulics</label>         <uniquesubsystem><subsystem>30</subsystem><label>reservoir</label>             <uniqueunit><unit>00</unit><label>pump</label>     </uniqueunit>     </uniquesubsystem> </uniquesystem></sns> 

i need extract values within each 'uniquesystem' element. in example above, under 'sns' element there 2 'uniquesystem' elements, , within each of these there 'uniquesubsystem' elements , 'uniqueunit' elements each 'label' elements. need extract data build treeview.

my problem extracting multiple elements using linq. how do this?

at moment have

var item = items in doc.descendants("sns").descendants("uniquesystem").descendants("system")                           orderby items.value                           select items.descendants("uniquesystem"); 

i think give me collection of 'uniquesystem' elements, need extract values of multiple elements within. can please help?

my next attmpt follows, giving me null reference exception:

var item = items in doc.descendants("sns").descendants("uniquesystem").descendants("system")                           orderby items.value                           select items.descendants("uniquesystem");                  foreach (var e in item)                 {                     string sys = e.descendants("system").firstordefault().value;                     string syslabel = e.descendants("system").descendants("label").firstordefault().value;                      string subsys = e.descendants("subsystem").firstordefault().value;                     string subsyslabel = e.descendants("subsystem").descendants("label").firstordefault().value;                      string unit = e.descendants("unit").firstordefault().value;                     string unitlabel = e.descendants("unit").descendants("label").firstordefault().value;                      buildsystemnodes(sys, syslabel);                     //getsubsystems(myitem);                 } 

so code have written below generate tree view. treeview class using in namespace system.web.ui.webcontrols. function o(n^3).

    public void processxml(string document)     {         var doc = xdocument.parse(document, loadoptions.none);         var uniquesystemlist = doc.element("sns").elements();          var treeview = new treeview();         string value = string.empty;         string text = string.empty;         foreach (var uniquesystem in uniquesystemlist)         {             value = uniquesystem.element("label").value.tostring();             text = uniquesystem.element("system").value.tostring();             var uniquesystemnode = new treenode(text, value);             var uniquesubsystemlist = uniquesystem.elements("uniquesubsystem");             foreach (var uniquesubsystem in uniquesubsystemlist)             {                 value = uniquesubsystem.element("label").value.tostring();                 text = uniquesubsystem.element("subsystem").value.tostring();                 var uniquesubsystemnode = new treenode(text, value);                 var uniqueunitlist = uniquesubsystem.elements("uniqueunit");                 foreach (var uniqueunit in uniqueunitlist)                 {                     value = uniqueunit.element("label").value.tostring();                     text = uniqueunit.element("unit").value.tostring();                     var uniqueunitnode = new treenode(text, value);                     uniquesubsystemnode.childnodes.add(uniqueunitnode);                 }                 uniquesystemnode.childnodes.add(uniquesubsystemnode);             }             treeview.nodes.add(uniquesystemnode);         }     }