Hi Felix ,
Small change in above solution ,
Create an attribute with name v_name ( declare a attribute of type if_wd_view in your view )
then in modify view write the below code,
WD_This->v-name = view ,
all above code remains same and pass the TAB_N ..i.e your popin table name on toggle method and write below code,
wd_table ?= view->get_element( 'TAB_N' ).
WD_THIS->TABLE_METHOD_HANDLE ?= wd_table1->_METHOD_HANDLER.
WD_THIS->TABLE_METHOD_HANDLE->SET_KEY_ATTRIBUTE_NAME( 'MATNR' ).
First time when you run code the parent filter will run , once you click on popin the popin toggle method runs so the popin filter will work , but at the time of popin filter the parent filter will not work so you need to refresh the application and run again.
But it will solve the popin filter problem , this i have posted late but it may help other new joiners .
Regards,
Vikram