Binding TextBox with list item

Question

I am unable bind value from the list to the textbox after SelectedIndexChanged event. The dropboxlist has AutoPostBack=true. But it doesn't fire this event

<asp:DropDownList ID="ddlRSM" runat="server" AutoPostBack="true">

</asp:DropDownList>

The DropdownList is loaded from C# code method

        private void GetRMS(string _ct, DropDownList ddl)
    {
        SPWeb web = SPContext.Current.Web;
        //  web = SPContext.Current.Site.OpenWeb("myteam");
        SPUser currentUser = web.CurrentUser;
        SPQuery query = new SPQuery();
        SPList list = web.Lists.TryGetList("RSM");
        string strQuery = string.Empty;
        strQuery = "<FieldRef Name='Title'/>";
        strQuery += "<Where><Eq><FieldRef Name='CustomerType'/><Value Type='Choice'>{0}</Value></Eq></Where>";
        strQuery = string.Format(strQuery, _ct);
        query.Query = strQuery;
        DataTable dt = list.GetItems(query).GetDataTable();

        ddl.DataSource = dt;

        ddl.DataTextField = "Title";
        ddl.DataValueField = "Title";
        ddl.DataBind();
        ddl.Items.Insert(0, "<-- Select " + _ct + " -->");
        ddl.SelectedIndex = 0;
        int idx = ddl.SelectedIndex;
    }

and this is the event which is not triggered

        protected void ddl_SelectedIndexChanged(object sender, EventArgs e)
    {

        string _ct = ddlRSM.SelectedItem.Text;
        SPWeb web = SPContext.Current.Web;
        SPQuery query = new SPQuery();
        SPList list = web.Lists.TryGetList("myList");
        string strQuery = string.Empty;
        strQuery = "<FieldRef Name='Address'/>";
        strQuery += "<Where><Eq><FieldRef Name='Title'/><Value Type='Text'>{0}</Value></Eq></Where>";
        strQuery = string.Format(strQuery, _ct);
        query.Query = strQuery;
        SPListItemCollection items = list.GetItems(strQuery);
        tbShipTo.Text = items[items.Count - 1]["Address"].ToString();

    }

Answer 1

You need to define the method to call on OnSelectedIndexChanged event

Replace your drop-down markup with:

<asp:DropDownList ID="ddlRSM" runat="server" AutoPostBack="true" OnSelectedIndexChanged="ddl_SelectedIndexChanged">
</asp:DropDownList>