c# - WPF binding failure with AvalonDock Theme -

i'm using avalondock wpf application , want use data binding changing theme.

viewmodel:

    private theme _avalondocktheme = new expressiondarktheme();     public theme avalondocktheme     {                 {             return _avalondocktheme;         }         set         {             if (_avalondocktheme != value)             {                 _avalondocktheme = value;                 raisepropertychanged("avalondocktheme");             }         }     } 

xaml:

<xcad:dockingmanager allowmixedorientation="true"         theme="{binding source={staticresource docktheme}}"          x:name="_dockingmanager">     <!-- content --> </xcad:dockingmanager> 

whe use following error message:

system.windows.data error: 5 : value produced bindingexpression not valid target property.; value='xceed.wpf.avalondock.themes.expressiondarktheme' bindingexpression:path=mainviewmodel.avalondocktheme; dataitem='app' (hashcode=47182344); target element 'collectionviewsource' (hashcode=42887454); target property 'source' (type 'object') 

i don't understand why binding fails. binding source , target both of type xceed.wpf.avalondock.themes.theme error message says target element of type collectionviewsource. why?

take @ question:

binding collectionviewsource within datatemplate

if doesn't help, please provide docktheme resource definition.