wpf - How to filter a collection when binding it to ItemsSource? -

i created treeview modelizes directories , files on hard drive. each treeviewitem has checkbox, binded isselected property. i'd achieve display each parent node count of selected files on total files count (10 / 12 10 files on twelve total selected).

is there way binding property ...?

<contentpresenter content="{binding myitems.count myitems.isselected, mode=onetime}"                   margin="2,0" /> 

there no way directly filter collection in binding. however, wpf allows filtering (and sorting , grouping) collections collectionviewsource.

one approach define collectionviewsource in resources of itemtemplate filters itemssource number of elements pass filter binding count property of collectionviewsource. have define filter in codebehind, though. this:

<treeview x:name="tree" itemssource="{binding items}">     <treeview.itemtemplate>         <hierarchicaldatatemplate itemssource="{binding childitems}">             <hierarchicaldatatemplate.resources>                 <collectionviewsource x:key="filtereditems"                                          source="{binding childitems}"                                         filter="filtereditems_onfilter" />             </hierarchicaldatatemplate.resources>             <textblock>                 <textblock.text>                     <multibinding stringformat="{} {0} of {1} selected">                         <binding path="count" source="{staticresource filtereditems}" />                         <binding path="itemssource.count" elementname="tree" />                     </multibinding>                 </textblock.text>             </textblock>         </hierarchicaldatatemplate>     </treeview.itemtemplate> </treeview> 

and in codebehind:

private void filtereditems_onfilter(object sender, filtereventargs e) {     var item = sender item;     return item.isselected; } 

i haven't tested should work in general. never know wpf, though...