Problem in following the webblog "Using TimeStamps: BSP Extensions"

Question

I try to follow the webblog "Using TimeStamps: BSP Extensions for a TimeStamp UI."
However, after I have created the method 'RESOLVE_MODEL_BINDING' and compiled it, it shows me an error message
<b>'Method "ADD_TO_CHECK_TABLE" is unknown or PROTECTED or PRIVATE.'</b>
This is some part of that code.
  model = m_page_context->get_model( model_name ).
  name = model->get_attribute_name( attribute_path = value_path ).
  valuelow = model->get_attribute( attribute_path = value_path ).
  IF id IS INITIAL.
    id = name.
  ENDIF.
  IF disabled IS INITIAL.
    bspmodel ?= model.
    bspmodel->add_to_check_table( control_id = name ).
  ENDIF.

Answer 1

I defined the bspmodel above the if block like the tutorial code.
DATA: model             TYPE REF TO if_bsp_model_binding,
      model_name        TYPE string,
      metadata          TYPE REF TO if_bsp_metadata_simple,
      metadata_base     TYPE REF TO if_bsp_metadata,
      value_path        TYPE string,
      is_valid          TYPE i,
      error_value       TYPE string,
      bspmodel          TYPE REF TO if_bsp_model.
I further looked into the interface <b>if_bsp_model</b> in my system. It doesn't include any interface, and only five methods were found:
1) INIT
2) GET_BINDING_INTERFACE
3) GET_ERRORS
4) INSTANTIATE
5) RESET_ERRORS