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:

OptgroupCombobox.cs

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:

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");

Created by jecray