选择屏幕－实现页签选择的效果

在R3中做的一个简单的例子，代码如下：

*&---------------------------------------------------------------------* *& Report  Z_TAB *& *&---------------------------------------------------------------------* *& *& *&---------------------------------------------------------------------*   REPORT  Z_TAB. TABLES: SSCRFIELDS,MARD.   SELECTION-SCREEN BEGIN OF SCREEN 1200 AS SUBSCREEN. SELECTION-SCREEN: BEGIN OF BLOCK BLK1 WITH FRAME TITLE T1.    PARAMETERS: WERKS LIKE MARD-WERKS. SELECTION-SCREEN: END OF BLOCK BLK1. SELECTION-SCREEN END   OF SCREEN 1200.   SELECTION-SCREEN BEGIN OF SCREEN 1300 AS SUBSCREEN. SELECTION-SCREEN: BEGIN OF BLOCK BLK2 WITH FRAME TITLE T2.    PARAMETERS: MATNR LIKE MARD-MATNR. SELECTION-SCREEN: END OF BLOCK BLK2. SELECTION-SCREEN END   OF SCREEN 1300.   SELECTION-SCREEN BEGIN OF TABBED BLOCK tabb1 FOR 14 LINES.   SELECTION-SCREEN TAB (15) tabs1 USER-COMMAND ucomm1                        DEFAULT SCREEN 1200.   SELECTION-SCREEN TAB (15) tabs2 USER-COMMAND ucomm2                        DEFAULT SCREEN 1300. SELECTION-SCREEN END OF BLOCK tabb1.   INITIALIZATION.   tabs1 = ''.   tabs2 = ''.   T1 = ''.   T2 = ''.