for(int i=1;i<=5;i++)
{
    GridView gv=this.FindControl("GridView"+i) as GridView;
    if(gv.Visible)
    //取出gv;
}

------解决方案--------------------
遍历吧 少年

------解决方案--------------------

for(int k=0;k<5;K++)
{
   GridView gridview=this.FindControl("GridView"+k) as GridView;
   if(gridview.Visible==ture)
   {
      Console.Write("恭喜您！找着儿了");

   }
   else
   {
     Console.Write("Come！Never give up");



   }


}