c# - How to bind a child `UserControl`'s Dependency Property, using `Style`, to a property of the host element's view-model? -

how bind child usercontrol's dependency property, using style, property of host element's view-model?

i tried code below, , myblock.blockisonlyone should bound view-model's property - mycontainerviewmodel.viewmodelisonlyone, via style's setter. reason doesn't work - myblock.blockisonlyone's value never changes, although mycontainerviewmodel.viewmodelisonlyone changes...

the container xaml:

<usercontrol x:class="myns.mycontainer"              ...              >     <usercontrol.datacontext>         <vc:mycontainerviewmodel x:name="thedatacontext"/>     </usercontrol.datacontext>      <grid>         <grid.resources>             <style targettype="{x:type vc:myblock}">                 <setter property="blockisonlyone" value="{binding viewmodelisonlyone}"/>                 <!-- tried too, no success: -->                 <!-- <setter property="blockisonlyone" value="{binding viewmodelisonlyone, elementname=thedatacontext}"/> -->             </style>         </grid.resources>         ...         <vc:myblock datacontext="{binding porta[0]}" />     </grid> </usercontrol> 

the container's viewmodel (only important part...):

[notifypropertychangedaspect] // handles inotifypropertychanged implementation... class mycontainerviewmodel{     ...     public bool viewmodelisonlyone { get; private set; }     ... } 

the myblock usercontrol:

class myblock : usercontrol{     ...     public static readonly dependencyproperty blockisonlyoneproperty = dependencyproperty.register(         "blockisonlyone", typeof (bool), typeof (myblock),          new propertymetadata(default(bool), blockisonlyone_propertychangedcallback));      private static void blockisonlyone_propertychangedcallback(dependencyobject dependencyobject, dependencypropertychangedeventargs a)     {         var @this = dependencyobject myblock;         if (@this == null) return;         trace.writeline(string.format("old: {0}, new: {1}", a.oldvalue, a.newvalue)); // never seems fire...     }      public bool blockisonlyone     {         { return (bool) getvalue(blockisonlyoneproperty); }         set { setvalue(blockisonlyoneproperty, value); }     }     ... } 

you should able reach view model property usercontrol using relativesource binding. idea search parent view view model set datacontext using ancestortype property... try this:

<style targettype="{x:type vc:myblock}">     <setter property="datacontext.blockisonlyone" value="{binding viewmodelisonlyone,      relativesource={relativesource ancestortype={x:type usercontrol}}}" /> </style> 

if picks child usercontrol.datacontext instead, either set relativesource.ancestorlevel property appropriate level, or use name/type of parent usercontrol instead:

<style targettype="{x:type vc:myblock}">     <setter property="blockisonlyone" value="{binding datacontext.viewmodelisonlyone,      relativesource={relativesource ancestortype={x:type yourprefix:mycontainer}}}" /> </style>