back issue of screen pai event

hi exports,

in order to realize:

1, two selection screens for one program;

2, by setting either one of the two selection screens could execute and display results in ALV grid.

3 ,the two selection screen could be switched to each other.

in my program , i created screen 100 as selection screen. screen 100 using subscreen  to realize two selection screen and two screens' switching . then if i directly create ALV grid using default screen(it's program SAPLSLVC_FULLSCREEN, screen 500), when i press back button ,the program finished instead of going back to selection screen.

so i created screen 200 to show ALV grid, and i can control the ALV grid screen(screen 200) go back to selection screen(screen 100) by using 'submit <program name> ' statement  under pai event of screen 200.

but here are problems, it can only go back to selection screen 1 even if i used selection screen 2 to run the program last time ,and all the earlier user setting data on selection screen are lost .

I would appreciate for your help!

Thanks,

Qi