How to read value from htmlb:inputField

I have a view (page fragment) that includes the following input field:

<htmlb:inputField id            = "search_vkona_topinfo"
                  value         = "//model/mv_topinfo_vkona"
                  size          = "12"
                  maxlength     = "12"
                  submitOnEnter = "true"
                  alignment     = "right" />

In the page controller in the event handler method I have the following piece of code:

DATA: data_input TYPE REF TO cl_htmlb_inputfield,
      lv_value   TYPE string.

** In htmlb_event_ex->event_id the value 'search_vkona_topinfo' is stored
data_input ?= cl_htmlb_manager=>get_data(
              request = runtime->server->request
              name = 'inputField'
              id = htmlb_event_ex->event_id ).

IF data_input IS NOT INITIAL.
  lv_value = data_input->value.
ENDIF.

Now I was expecting this would be simple and just work, however, unfortunately in data_input->value there is no value. Any ideas what could be the problem?

PS: The data binding also does not seem to work. In my model the field mv_topinfo_vkona is empty