How to capture expand node event in SALV Tree? - treeview

Question

I've created an ALV tree view with use of the class CL_SALV_TREE.
Everything works fine but I'd like to grap the event when a node is expanded, for filling in a function that automatically resizes the tree columns.
My problem is, that the expanding event is the private method HANDLE_EXPAND_NC of class CL_GUI_ALV_TREE and I actually don't know how to capture this event. I'm open for any ideas and thanks for your time.

Answer 1

As far as I know, you can only be notified if a folder is expanded that does not yet contain children (the _NC part of the method/event name signifies that). This is intended for lazy loading of the tree. The tree displays in the SAP menu or the IMG are a good example for that - you can actually see parts of the tree being loaded when you expand the top-level nodes.
If that is sufficient for you, use the event EXPAND_EMPTY_FOLDER of the interface IF_SALV_EVENTS_TREE, implemented by CL_SALV_EVENTS_TREE. There doesn't seem to be a good demo program for this though.

Answer 2

Here is a minimal reproducible example which shows that the event EXPAND_EMPTY_FOLDER is triggered when you expand a node which has no children initially, a child node is added during that event:
CLASS lcl_app DEFINITION.
PUBLIC SECTION.
METHODS pbo
RAISING
cx_salv_error.
PRIVATE SECTION.
DATA: salv TYPE REF TO cl_salv_tree,
scarrs TYPE STANDARD TABLE OF scarr.
METHODS on_expand_empty_folder
FOR EVENT expand_empty_folder
OF cl_salv_events_tree
IMPORTING node_key.
ENDCLASS.
CLASS lcl_app IMPLEMENTATION.
METHOD pbo.
IF salv IS NOT BOUND.
cl_salv_tree=>factory( EXPORTING r_container = cl_gui_container=>screen0
IMPORTING r_salv_tree = salv
CHANGING t_table = scarrs ).
DATA(lo_settings) = salv->get_tree_settings( ).
lo_settings->set_hierarchy_size( 30 ).
DATA(event) = salv->get_event( ).
salv->get_functions( )->add_function( name = 'NEW' text = 'NEW' tooltip = '' position = 1 ).
SET HANDLER on_expand_empty_folder FOR event.
SELECT * FROM scarr INTO TABLE #DATA(local_scarrs).
LOOP AT local_scarrs REFERENCE INTO DATA(scarr).
salv->get_nodes( )->add_node(
related_node = space " (root node)
relationship = cl_gui_column_tree=>relat_last_child
text = |{ scarr->carrid } - { scarr->carrname }|
data_row = scarr->*
folder = abap_true
expander = abap_true ).
ENDLOOP.
salv->display( ).
ENDIF.
LOOP AT SCREEN.
screen-active = '0'.
MODIFY SCREEN.
ENDLOOP.
ENDMETHOD.
METHOD on_expand_empty_folder.
TRY.
DATA(scarr) = CAST scarr( salv->get_nodes( )->get_node( node_key )->get_data_row( ) )->*.
salv->get_nodes( )->add_node(
related_node = node_key
relationship = cl_gui_column_tree=>relat_last_child
text = |Node added at time of expand below { scarr-carrid }| ).
CATCH cx_root INTO DATA(lx).
MESSAGE lx TYPE 'I' DISPLAY LIKE 'E'.
LEAVE PROGRAM.
ENDTRY.
ENDMETHOD.
ENDCLASS.
PARAMETERS dummy.
LOAD-OF-PROGRAM.
DATA(app) = NEW lcl_app( ).
AT SELECTION-SCREEN OUTPUT.
TRY.
app->pbo( ).
CATCH cx_root INTO DATA(lx).
MESSAGE lx TYPE 'S' DISPLAY LIKE 'E'.
ENDTRY.