Adding custom controller to standard BSP application

Hi All,

I am working on one standard BSP application, this application is based on MVC model. In this BSP application, i have to add three custom fields(dropdownlist boxes) to the view. Since this is standard BSP application i am unable to add attributes related to the custom fields in  'Standard Controller' & 'Standard Model' classes, so i created one 'Custom Controller' class and one 'Custom Model' class. In brief,

Custom controller is having a public attribute 'ABC' type referenced to Custom Model class.

Custom Model is having public attributes 'var1' 'var2' 'var3' 'tab1' 'tab2' 'tab3'.

In standardview, I added public attribute 'zmodel' type referenced to 'Custom Model' class and passed the 'tab1' of Custom model class to 'table' property of 'dropdownlistbox'.

           <htmlb: dropdownListbox id = "ID01"

                                                 table = "//zmodel/tab1"

                                                   ..........................

                                                   ..........................

                                                 selection = "//zmodel/var1"/>

Now if i try to execute the application it is generating an exception 'Access with Null reference variable is not possible'. I set the break-point in 'Do_Init' method of my custom controller class, but it is not triggering i.e. my custom controller is not getting called. I am unable to rectify this error. Please suggest whether i am doing it(MVC model data binding) in right way and is it advisable to add custom controller & model to the standard BSP application. Please guide or suggest any alternative solution to this. Thank you very much for your valuable time.

Regards

Siva Shankar