Internal Table Moving

Dear Friends

i am developing small BSP application

when i enter material code and click on the preview button material descriptions came to page and end of the list another button came with description download

when i click on that the list must download to as excel file.

so my requirement is in my preview button data load to itab so in my event handler i want to use these loaded iteb in download event also

but when i click onthe download button that itab was initialized

please help me to solve this