I've built a custom datatype that creates a list of features for a group of venues (in this case, the libraries in our area), which, for the most part, is working properly.

The trouble I'm having is getting a field in the user control to dynamically update with the prevalues retrieved from another datatype. Currently the users pick the icon list, then manually save & reload the data type before the prevalues appear in the "Icon type" drop-down field...

Do I need to add a condition to pick up on a postback, and, if so, how do I do this?

The code for the "Add venue features" section is below...

    public class VenueItems : umbraco.cms.businesslogic.datatype.DataEditorSettingType
    {
        private Panel p = new Panel();
        private TextBox tb = new TextBox();        
        private DropDownList ddl = new DropDownList();

        public override string Value
        {
            get
            {
                return tb.Text;
            }
            set
            {
                tb.Text = value;
            }
        }

        public override System.Web.UI.Control RenderControl(DataEditorSetting sender)
        {         
            tb.CssClass = "itemsAdded";           
            tb.ID = sender.GetName() + "_values";

            ddl.CssClass = "newItemClass";
            ddl.ID = sender.GetName() + "_classes";

            // get ID of this data type from querystring
            int dataTypeId;
            if (Int32.TryParse(HttpContext.Current.Request["id"], out dataTypeId))
            {
                // get all data editor settings for this data type
                DataEditorSettingsStorage des = new DataEditorSettingsStorage();
                var settings = des.GetSettings(dataTypeId);
                Setting<string, string> thisSetting = settings.Find(s => s.Key == this.Prevalues[0]);
                if (thisSetting.Key != null)
                {
                    int selectedDtId;
                    if (Int32.TryParse(thisSetting.Value.ToString(), out selectedDtId))
                    {
                        var prevalues = PreValues.GetPreValues(selectedDtId);
                        if (prevalues.Count > 0)
                        {
                            for (int i = 0; i < prevalues.Count; i++)
                            {
                                var prevalue = (PreValue)prevalues[i];
                                if (!String.IsNullOrEmpty(prevalue.Value))
                                {
                                    ddl.Items.Add(new ListItem(prevalue.Value, prevalue.DataTypeId.ToString()));
                                }
                            }
                        }
                        else
                        {
                            ddl.Items.Add("Failed to find the icon list...");
                        }
                    }
                }
                else
                {
                    ddl.Items.Add("Failed to find the icon list...");
                }
            }            

            string html1 = "<div class='values'>";
            html1 += "</div>";
            html1 += "<div class='venueItemsInputs'>";
            html1 += "<hr/>";
            html1 += "<span class='inputLabel'>Icon type:</span>";

            string html2 = "<span class='inputLabel'>Item:</span>";
            html2 += "<input type='text' class='newItemInput' /><br/>";
            html2 += "<span class='inputLabel'>Detail:</span>";
            html2 += "<input type='text' class='newItemDetailInput' />";
            html2 += string.Format(" <a onclick=\"valuesCustomControlAddValue(this); return false;\" href='#' class='Add'>Add Item</a>");
            html2 += "</div>";

            p.Controls.Add(new System.Web.UI.LiteralControl("<div class='itemsCustomControl'>"));
            p.Controls.Add(new System.Web.UI.LiteralControl(html1));
            p.Controls.Add(ddl);
            p.Controls.Add(new System.Web.UI.LiteralControl("<br/>"));
            p.Controls.Add(new System.Web.UI.LiteralControl(html2));
            p.Controls.Add(tb);
            p.Controls.Add(new System.Web.UI.LiteralControl("</div>"));


            System.Web.UI.Page page = (System.Web.UI.Page)HttpContext.Current.Handler;

            page.ClientScript.RegisterClientScriptInclude(
                "Shropshire.Web.DESettingType.VenueItems.Resources.VenueItems.js",
                page.ClientScript.GetWebResourceUrl(typeof(VenueItems), "Shropshire.Web.DESettingType.VenueItems.Resources.VenueItems.js"));

            HtmlHead head = (HtmlHead)page.Header;
            HtmlLink link = new HtmlLink();
            link.Attributes.Add("href", page.ClientScript.GetWebResourceUrl(typeof(VenueItems), "Shropshire.Web.DESettingType.VenueItems.Resources.VenueItems.css"));
            link.Attributes.Add("type", "text/css");
            link.Attributes.Add("rel", "stylesheet");
            head.Controls.Add(link);
            
            return p;
        }
    }