How to fetch all selected record from all pages of gridview at time in buttonclick event?

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ASP.NET

I am showing record in grid(contain checkbox as first column) that has paging.If I select record in page one and move to second page selected record from first get unchecked.Shall I make enable viewstate?What will happen?Can I able to fetch all record(id) which are selected from all pages of grid at a time in button click event?

foreach (GridViewRow rowItem in Gridview1.Rows)
{
}