How to debug silverlight applications?

Question

I want to trace the code when the data is loaded. (VS2010 Silverlight4)

<riaControls:DomainDataSource Name="domainDS" HorizontalAlignment="Left" VerticalAlignment="Top" QueryName="GetPlanQuery" LoadedData="domainDS_LoadedData">
...
</riaControls:DomainDataSource>

In the code behind:

private void domainDS_LoadedData(object sender, LoadedDataEventArgs e)
{
   //break points here will never be hit
}

Is there any way to debug the code even the project is compiled to an XAP file and added to some page in another web project? I have all the project source code. Thanks.