//全选
for (int i = 0; i < CheckBoxList1.Items.Count; i++)
{
CheckBoxList1.Items[i].Selected = true;
}
//反选
for (int i = 0; i < CheckBoxList1.Items.Count; i++)
{
if(CheckBoxList1.Items[i].Selected)
CheckBoxList1.Items[i].Selected = false;
else
CheckBoxList1.Items[i].Selected = true;
}