创建一个带分组功能的下拉列表框控件

这是http://www.codeplex.com/上的一个开源项目SharpPieces , 不过作者目前只开发了这一个控件, 实现了页面PostBack后保存控件状态 .分享一下 .
效果如图:



源码下载地址: 点击查看 
http://www.codeplex.com/SharpPieces/Release/ProjectReleases.aspx?ReleaseId=6782

源代码如下 作者有详细的注释

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using System;using System.Collections.Generic;using System.Text;using System.Web.UI.WebControls;using System.Web;namespace ASPNETControls{    public class OptgroupCombobox : DropDownList    {        private const string optGroupAttributeKey = "optgroup";        /// <summary>        /// Override the SaveViewState to save the control's Attributes        /// </summary>        /// <returns></returns>        protected override object SaveViewState()        {            // Create an object array with one element for the CheckBoxList's            // ViewState contents, and one element for each ListItem in skmCheckBoxList            object[] state = new object[this.Items.Count + 1];            object baseState = base.SaveViewState();            state[0] = baseState;            // Now, see if we even need to save the view state            bool itemHasAttributes = false;            for (int i = 0; i < this.Items.Count; i++)            {                if (this.Items[i].Attributes.Count > 0)                {                    itemHasAttributes = true;                    // Create an array of the item's Attribute's keys and values                    object[] attribKV = new object[this.Items[i].Attributes.Count * 2];                    int k = 0;                    foreach (string key in this.Items[i].Attributes.Keys)                    {                        attribKV[k++] = key;                        attribKV[k++] = this.Items[i].Attributes[key];                    }                    state[i + 1] = attribKV;                }            }            // return either baseState or state, depending on whether or not            // any ListItems had attributes            if (itemHasAttributes)                return state;            else                return baseState;        }        /// <summary>        /// Override the LoadViewState to load the control's Attributes        /// </summary>        protected override void LoadViewState(object savedState)        {            if (savedState == null)                return;            // see if savedState is an object or object array            if (savedState is object[])            {                // we have an array of items with attributes                object[] state = (object[]) savedState;                base.LoadViewState(state[0]);   // load the base state                for (int i = 1; i < state.Length; i++)                {                    if (state[i] != null)                    {                        // Load back in the attributes                        object[] attribKV = (object[]) state[i];                        for (int k = 0; k < attribKV.Length; k += 2)                            this.Items[i - 1].Attributes.Add(attribKV[k].ToString(),                                                           attribKV[k + 1].ToString());                    }                }            }            else                // we have just the base state                base.LoadViewState(savedState);        }        protected override void RenderContents(System.Web.UI.HtmlTextWriter writer)        {            if (this.Items.Count > 0)            {                bool selected = false;                bool optGroupStarted = false;                for (int i = 0; i < this.Items.Count; i++)                {                    ListItem item = this.Items[i];                    if (item.Enabled)                    {                        if (item.Attributes[optGroupAttributeKey] != null)                        {                            if (optGroupStarted)                                writer.WriteEndTag("optgroup");                            writer.WriteBeginTag("optgroup");                            writer.WriteAttribute("label", item.Text);                            writer.Write('>');                            writer.WriteLine();                            optGroupStarted = true;                        }                        else                        {                            writer.WriteBeginTag("option");                            if (item.Selected)                            {                                if (selected)                                {                                    this.VerifyMultiSelect();                                }                                selected = true;                                writer.WriteAttribute("selected", "selected");                            }                            writer.WriteAttribute("value", item.Value, true);                            if (item.Attributes.Count > 0)                            {                                item.Attributes.Render(writer);                            }                            if (this.Page != null)                            {                                this.Page.ClientScript.RegisterForEventValidation(this.UniqueID, item.Value);                            }                            writer.Write('>');                            HttpUtility.HtmlEncode(item.Text, writer);                            writer.WriteEndTag("option");                            writer.WriteLine();                        }                    }                }                if (optGroupStarted)                    writer.WriteEndTag(optGroupAttributeKey);            }        }        /// <summary>        /// Adds a optgroup element.        /// </summary>        public void AddGroup(string text)        {            ListItem li = new ListItem();            li.Text = text;            li.Attributes[optGroupAttributeKey] = "1";            this.Items.Add(li);        }    }}

使用方法:

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this.cboTest.Items.Add("Choose an item");this.cboTest.AddGroup("Computers");this.cboTest.Items.Add("Monitor");this.cboTest.Items.Add("Mouse");this.cboTest.Items.Add("Keyboard");this.cboTest.AddGroup("Phones");this.cboTest.Items.Add("iPhone");this.cboTest.Items.Add("gPhone");