Event Blocks for Selection Screens

selection screen 是一种特殊的对话框 screen是用ABAP 语句申明的，主要是指
selection-screen begin of screen <xxx>.
不同的selection screen事件(PAI,PBO，用户输入)是selection screen处理器来控制的.你可以在自己的程序中自己编程来出来这些事件.The selection screen processor 控制 selection screen的flow logic (一般是在tcode se51中的screen painter里设置.).

PBO，对应的ABAP statement是AT SELECTION-SCREEN OUTPUT
PAI,对应的ABAP statement 是 AT SELECTION-SCREEN 以及

… { OUTPUT } –>用于PBO
| { ON {para|selcrit} }
| { ON END OF selcrit }
| { ON BLOCK block }
| { ON RADIOBUTTON GROUP radi }
| { }
| { ON {HELP-REQUEST|VALUE-REQUEST}
|   FOR {para|selcrit-low|selcrit-high} }
| { ON EXIT-COMMAND }.

你不必自己建立screen flow logic,也不需要建立自己的对话框模块的PBO或PAI 事件

Data is passed between selection screen and ABAP program using the fields (parameters and selection tables) which you create in the selection screen definition in the declaration part of the ABAP program.