Cannot create instances of the Types contained in the loaded Silverlight Prism XAP modules

My Silverlight PRISM application is loading several XAP modules. I want to be able to get access to the types contained in the loaded modules so I could create instances of the views and modelviews BEFORE shell is activated. I am trying to implement something like this:

                AggregateCatalog.Changed+=(o, e)=>
                                         开发者_如何学编程 {
                                              var type =
                                                  Type.GetType(
                                                      "mytype, assemblyname");
}

but the type is always null :( Please help.