1.SYSTEM-CALL:DY_GET_FOCUS
说明：获得屏幕焦点
参数：
ID 'SSCREENNAM' FIELD CURRSUBSCREEN
ID 'SSCREENNBR' FIELD CURRSUBSCREENNO
ID 'MSCREENNAM' FIELD CURRSCREEN
ID 'MSCREENNBR' FIELD CURRSCREENNO
ID 'FIELDNAME' FIELD CURSOR_FIELD
ID 'FIELDOFFS' FIELD DUMMYOFFS
ID 'LINE' FIELD CURSOR_LINE.