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");