ABAP Web Dynpro - get the selected table values

Hello,

I'm new at Abap Web Dynpro and I try to get some information of an ALV when I click on a button. In my layout view I have a ViewContainerUIElement where I the ALV is implemented. Under this element I have a button that should read the selected data row in the ALV.

I tried this to get the data:

CHANGING is my ALV-tab.

DATA: context_element type ref to if_wd_context_element, 
      context_data    type ref to if_wd_context_node.

context_element = wdevent->get_context_element( 'CHANGING' ).
context_data    = wdevent->get_context_element( 'CHANGING' ).


*then call the get_index method..
context_element->get_index( ).
context_data->get_selected_elements( ).

When I test the Web Dynpro in IE it does not work.

Can anybody helps me?

Regards, Markus