ABAP 拖放事件 ( ON_DRAG )
Sap中常用的OO屏幕控件一般都会带有拖放事件
例如CL_GUI_SIMPLE_TREE：
其事件参数为：
CL_GUI_ALV_GRID：
其事件参数为：
CL_GUI_ALV_TREE：
其事件参数为：
我们以SAP中的一个名为BCALV_GRID_DND_TREE 的DEMO程序为例以展示拖放的效果
该程序使用docking将屏幕一分为二，一边用于放置ALV_TREE，另一边则放置了ALV_GRID
作为ALV_TREE的数据池
ALV_TREE的事件构造器：
*----------------------------------------------------------------------*
* INCLUDE BCALV_TREE_EVENT_REC_DRAGDROP *
*----------------------------------------------------------------------*
CLASS CL_TREE_EVENT_RECEIVER DEFINITION.
PUBLIC SECTION.
* double click item
METHODS HANDLE_DOUBLE_CLICK
FOR EVENT NODE_DOUBLE_CLICK OF CL_GUI_ALV_TREE
IMPORTING NODE_KEY.
* Drag
METHODS HANDLE_ON_DRAG
FOR EVENT ON_DRAG OF CL_GUI_ALV_TREE
IMPORTING DRAG_DROP_OBJECT
FIELDNAME
NODE_KEY.
PRIVATE SECTION.
ENDCLASS.
*---------------------------------------------------------------------*
* CLASS CL_TREE_EVENT_RECEIVER IMPLEMENTATION
*---------------------------------------------------------------------*
CLASS CL_TREE_EVENT_RECEIVER IMPLEMENTATION.
* handle double_click
METHOD HANDLE_DOUBLE_CLICK.
CHECK NOT NODE_KEY IS INITIAL.
PERFORM DISPLAY_FLIGHTS USING NODE_KEY.
ENDMETHOD.
* Drag & Drop
METHOD HANDLE_ON_DRAG.
CHECK NOT NODE_KEY IS INITIAL.
PERFORM DISPLAY_FLIGHTS USING NODE_KEY.
CALL METHOD CL_GUI_CFW=>SET_NEW_OK_CODE EXPORTING NEW_CODE =
FCODE_ENTR.
ENDMETHOD.
ENDCLASS.
*
DATA: TREE_EVENT_RECEIVER TYPE REF TO CL_TREE_EVENT_RECEIVER.
通过ON_DRAG事件的参数NODE_KEY读取当前节点或其子节点的数据：
FORM display_flights USING p_node_key TYPE lvc_nkey.
DATA: ls_spfli TYPE spfli,
lt_children TYPE lvc_t_nkey WITH HEADER LINE.
REFRESH gt_sflight.
CALL METHOD tree1->get_outtab_line
EXPORTING i_node_key = p_node_key
IMPORTING e_outtab_line = ls_spfli.
* CHECK NOT GT_DB_SPFLI IS INITIAL.
IF ls_spfli IS INITIAL.
CALL METHOD tree1->get_children
EXPORTING i_node_key = p_node_key
IMPORTING et_children = lt_children[].
CHECK NOT lt_children[] IS INITIAL.
LOOP AT lt_children.
CALL METHOD tree1->get_outtab_line
EXPORTING i_node_key = lt_children
IMPORTING e_outtab_line = ls_spfli.
SELECT * FROM sflight APPENDING TABLE gt_sflight
WHERE carrid = ls_spfli-carrid
AND connid = ls_spfli-connid.
READ TABLE gt_scarr WITH KEY carrid = ls_spfli-carrid.
scarr = gt_scarr.
ENDLOOP.
ELSE.
SELECT * FROM sflight INTO TABLE gt_sflight
WHERE carrid = ls_spfli-carrid
AND connid = ls_spfli-connid.
READ TABLE gt_scarr WITH KEY carrid = ls_spfli-carrid.
scarr = gt_scarr.
ENDIF.
IF gt_sflight[] IS INITIAL. "AND NOT GRID IS INITIAL.
MESSAGE i000(0k) WITH TEXT-115 space space space.
CLEAR scarr.
ELSE.
flg_new = selected.
ENDIF.
ENDFORM. " DISPLAY_FLIGHTS
展示效果请见DEMO程序：BCALV_GRID_DND_TREE
个人感觉double_click完全可以替代ON_DRAG的功能，这也可能是拖放在SAP中并不常见的原因吧