How do I move this sample aspx code to aspx.cs (to implement code behind)?

I have a dropdownlist which is populate开发者_StackOverflowd with data from an SQL db. This is what I might have in the aspx file. How do I move (as much as possible) the code from the aspx file to the aspx.cs file to implement the code behind technique? I mean at least the SELECT portion. Thanks.

<asp:DropDownList ID="DropDownList1" ... runat="server"/>
...
<asp:SqlDataSource ID="SqlDataSource1" runat="server" 
ConnectionString="<%$ ConnectionStrings:Pubs %>"
SelectCommand="SELECT [au_id], [au_lname], [au_fname], [state] FROM [authors] WHERE    [state] = @state">
<SelectParameters>
<asp:ControlParameter Name="state" ControlID="DropDownList1"  PropertyName="SelectedValue" />
</SelectParameters>
</asp:SqlDataSource>

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suppose you are binding a grid with data source SqlDataSource1 then you can catch SelectedIndexChanged event in codebehind and get data to bind the grid like this:

ASPX file:

<asp:DropDownList ID="DropDownList1" runat="server" 
         OnSelectedIndexChanged="ddlChanged" />

C# (codebehind):

protected void ddlChanged(object sender, EventArgs e)
{
    var cs=..;//get connection string
    using(var con=new SqlConnection(cs))
    {
        using(var com=new SqlCommand(con))
        {
            com.Open();
            com.CommandType = CommandType.Text;
            com.CommandText="SELECT [au_id], [au_lname], [au_fname], [state] 
                 FROM [authors] WHERE [state] = @state";

            var state=....;//GET VALUE OF STATE FROM DROPDOWN
            var p = com.Parameters.Add("@state");//set other properties
            p.Value = state;

            using(var adptr=new SqlDataAdapter(com))
            {
                var dtb=new DataTable();
                adptr.Fill(dtb);
                grid.DataSource=dtb;
                grid.DataBind();
            }
        }
    }
}

---

The SelectCommand is a property of the datasource object you are using. These can be applied in the code behind as needed, but you may want to do it in an overridden Init page function as this might be used quite early on in the asp.net page life cycle. for eg, although I'm not sure exactly where.

protected override OnInit(object sender, EventArgs e)
{
    dsMySource.SelectCommand = "SELECT [au_id], [au_lname], [au_fname], [state] FROM [authors] WHERE [state] = @state"

}

You are also going to have to make sure the @state parameter is used correctly in the code behind as well, this can be accessed also as a property (dsMySource.SelectParameters).