c# - Silverlight: When is a dependency property available? -

i setting dependency property in xaml (silverlight 4):

<my:topsearchbar x:name="topsearchbar" grid.row="0" navigator="{binding elementname=navigationframe}" horizontalalignment="stretch" verticalalignment="top" /> 

i need register navigation events of navigationframe. however, following fails null pointer exception:

    public topsearchbar()     {         // required initialize variables         initializecomponent();          loaded += new routedeventhandler(topsearchbar_loaded);     }      void topsearchbar_loaded(object sender, routedeventargs e)     {         // navigator null         navigator.navigated += new navigatedeventhandler(navigated);     } 

when right time register these event handlers? tried doing in property setter, breakpoint never hit:

    public frame navigator     {         { return getvalue(navigatorproperty) frame; }         set { setvalue(navigatorproperty, value); }     } 

bindings not use navigator property. instead, binding class accesses navigatorproperty field, of type dependencyproperty, directly, , sets value.

in code behind, can overridemetadata on navigatorproperty object. create propertymetadata includes propertychangedcallback, , add event handler there. aware, overridemetadata works on instances of type specify, specify lowest 1 need (topsearchbar, probably), , careful.

dependencyproperty.overridemetadata method