wpf - Silverlight treeview. Cannot bind "IsExpanded" property -

i have treeview control , want bind tree nodes' isexpanded property datasource items!

but have exception:

system.windows.markup.xamlparseexception occurred   message=set property '' threw exception.    stacktrace:        @ system.windows.application.loadcomponent(object component, uri resourcelocator)        @ silverlighttree.bstreeview.initializecomponent()        @ silverlighttree.bstreeview..ctor()   innerexception: system.notsupportedexception        message=cannot set read-only property ''.        stacktrace:             @ ms.internal.xamlmemberinfo.setvalue(object target, object value)             @ ms.internal.xamlmanagedruntimerpinvokes.setvalue(xamltypetoken intype, xamlqualifiedobject& inobj, xamlpropertytoken inproperty, xamlqualifiedobject& invalue)        innerexception:  

inner exception:

{system.notsupportedexception: cannot set read-only property ''. 

xaml:

<grid x:name="layoutroot">     <controls:treeview name="treeview" selecteditemchanged="treeview_selecteditemchanged"                        style="{binding  treeviewconnectinglines}" borderbrush="{x:null}">         <controls:treeview.itemtemplate>             <toolkit:hierarchicaldatatemplate itemssource="{binding children}">                 <stackpanel orientation="horizontal"  background="transparent">                     <toolkitdrag:contextmenuservice.contextmenu>                         <toolkitdrag:contextmenu loaded="contextmenu_loaded"                                                  opened="contextmenu_opened"/>                     </toolkitdrag:contextmenuservice.contextmenu>                     <image source="{binding path=type.icon}"  width="20" height="20" />                     <textblock text="{binding path=fulldescription}"   height="20"                                textalignment="center" horizontalalignment="center" />                 </stackpanel>             </toolkit:hierarchicaldatatemplate>         </controls:treeview.itemtemplate>         <controls:treeview.itemcontainerstyle>             <style targettype="controls:treeviewitem">                 <setter property="isexpanded" value="{binding isexpanded}"></setter>             </style>         </controls:treeview.itemcontainerstyle>          </controls:treeview> </grid> 

and data items:

public interface inode {     nodetype type { get; set; }     bool isselected { get; set; }     bool isexpanded { get; set; }     list<inode> children{get;set;}; } 

the quickest way subclass both treeview , treeviewitem, example:

public class bindabletreeviewitem : treeviewitem {     protected override dependencyobject getcontainerforitemoverride()     {         var itm = new bindabletreeviewitem();         itm.setbinding(treeviewitem.isexpandedproperty, new binding("isexpanded") { mode = bindingmode.twoway });          return itm;     } }  public class bindabletreeview : treeview {     protected override dependencyobject getcontainerforitemoverride()     {         var itm = new bindabletreeviewitem();         itm.setbinding(treeviewitem.isexpandedproperty, new binding("isexpanded") { mode = bindingmode.twoway });          return itm;     } } 

unfortunately you'll lose default theming of treeview when subclassing. weakness of silverlight theming concept. alternatively use custom attached property or behavior traverses tree , sets bindings outside. because tree nodes created lazily on-demand though, you'd have listen expanded event once each node has not yet been rendered, set bindings in event handler each of children after waiting layout pass.