I traied but it didnt work, thanks
My solution is:
file.aspx
<asp:dropdownlist runat="server" id="sFP" datasource="<%# fillDataList((string)DataBinder.Eval(Container.DataItem, "C_ID")) %>" datatextfield="Title" xmlns:asp="#unknown"></asp:dropdownlist>
file.aspx.cs
public DataView fillDataList(string id)
{
DataSet data = DB.GetData("SELECT * FROM … WHERE FK =" + id + ")", false);
DataView myView = data.Tables[0].DefaultView;
return myView;
}