How to change the GridView page Index

How to change Gridview pages based on the dropdown list selected index? the dropdown list开发者_运维技巧 is not inside the gridview, any help would be appreciated.

    <asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True" 
            onselectedindexchanged="DropDownList1_SelectedIndexChanged">    
    </asp:DropDownList>

protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{
    GridView1.PageIndex = DropDownList1.SelectedItem.Value;
    GridView1.DataSource = datatable;
    GridView1.DataBind();
}

What you need to do is set the GridView's PageSize property to the value of your DropDownList's selected item value:

private void DropDownListPageSize_SelectedIndexChanged(object sender, EventArgs e)
{
    gridview.PageSize = DropDownListPageSize.SelectedValue;
}