if(GridView.Rows.Count == 0)
{
// Do Something
}

DataTable data = DAL.getdata();
if (data.Rows.Count == 0)
{
    ShowEmptyData();
}
else
{
    Grid.DataSource = dt;
    Grid.DataBind();
}

<asp:GridView runat="server">
<EmptyDataTemplate>The grid is empty</EmptyDataTemplate>
</asp:GridView>

int rowCount = GridView.Rows.Count; // returns zero

GridView.DataBind();

rowCount = GridView.Rows.Count; // returns actual row count