ListItems attributes in a DropDownList are lost on postback?

Simple solution is to add the tooltip attributes in the pre-render event of the dropdown. Any changes to the state should be done at pre-render event.

sample code :

protected void drpBrand_PreRender(object sender, EventArgs e)
        {
            foreach (ListItem _listItem in drpBrand.Items)
            {
                _listItem.Attributes.Add("title", _listItem.Text);
            }
            drpBrand.Attributes.Add("onmouseover", "this.title=this.options[this.selectedIndex].title");
        }

I had the same problem and wanted to contribute this resource where the author created an inherited ListItem Consumer to persist attributes to ViewState. Hopefully it will save someone the time I wasted until I stumbled on it.

protected override object SaveViewState()
{
    // create object array for Item count + 1
    object[] allStates = new object[this.Items.Count + 1];

    // the +1 is to hold the base info
    object baseState = base.SaveViewState();
    allStates[0] = baseState;

    Int32 i = 1;
    // now loop through and save each Style attribute for the List
    foreach (ListItem li in this.Items)
    {
        Int32 j = 0;
        string[][] attributes = new string[li.Attributes.Count][];
        foreach (string attribute in li.Attributes.Keys)
        {
            attributes[j++] = new string[] {attribute, li.Attributes[attribute]};
        }
        allStates[i++] = attributes;
    }
    return allStates;
}

protected override void LoadViewState(object savedState)
{
    if (savedState != null)
    {
        object[] myState = (object[])savedState;

        // restore base first
        if (myState[0] != null)
            base.LoadViewState(myState[0]);

        Int32 i = 1;
        foreach (ListItem li in this.Items)
        {
            // loop through and restore each style attribute
            foreach (string[] attribute in (string[][])myState[i++])
            {
                li.Attributes[attribute[0]] = attribute[1];
            }
        }
    }
}

If you only want to load the listitems on the first load of the page then you will need to enable ViewState so that the control can serialize its state there and reload it when the page posts back.

There are several places where ViewState can be enabled - check the <pages/> node in the web.config and also in the <%@ page %> directive at the top of the aspx file itself for the EnableViewState property. This setting will need to be true for ViewState to work.

If you don't want to use ViewState, simply remove the if (!IsPostBack) { ... } from around the code that adds the ListItems and the items will be recreated on each postback.

Edit: I apologize - I misread your question. You are correct that the attributes do no survive postback as they are not serialized in ViewState. You must re-add those attributes on each postback.

Thanks, Laramie. Just what I was looking for. It keeps the attributes perfectly.

To expand, below is a class file I created using Laramie's code to create a dropdownlist in VS2008. Create the class in the App_Code folder. After you create the class, use this line on the aspx page to register it:

<%@ Register TagPrefix="aspNewControls" Namespace="NewControls"%>

You can then put the control on your webform with this

<aspNewControls:NewDropDownList ID="ddlWhatever" runat="server">
                                                </aspNewControls:NewDropDownList>

Ok, here's the class...

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Security.Permissions;
using System.Linq;
using System.Text;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace NewControls
{
  [DefaultProperty("Text")]
  [ToolboxData("<{0}:ServerControl1 runat=server></{0}:ServerControl1>")]
  public class NewDropDownList : DropDownList
  {
    [Bindable(true)]
    [Category("Appearance")]
    [DefaultValue("")]
    [Localizable(true)]

    protected override object SaveViewState()
    {
        // create object array for Item count + 1
        object[] allStates = new object[this.Items.Count + 1];

        // the +1 is to hold the base info
        object baseState = base.SaveViewState();
        allStates[0] = baseState;

        Int32 i = 1;
        // now loop through and save each Style attribute for the List
        foreach (ListItem li in this.Items)
        {
            Int32 j = 0;
            string[][] attributes = new string[li.Attributes.Count][];
            foreach (string attribute in li.Attributes.Keys)
            {
                attributes[j++] = new string[] { attribute, li.Attributes[attribute] };
            }
            allStates[i++] = attributes;
        }
        return allStates;
    }

    protected override void LoadViewState(object savedState)
    {
        if (savedState != null)
        {
            object[] myState = (object[])savedState;

            // restore base first
            if (myState[0] != null)
                base.LoadViewState(myState[0]);

            Int32 i = 1;
            foreach (ListItem li in this.Items)
            {
                // loop through and restore each style attribute
                foreach (string[] attribute in (string[][])myState[i++])
                {
                    li.Attributes[attribute[0]] = attribute[1];
                }
            }
        }
    }
  }
}