asp.net DropDownList自定义控件，让你的分类更清晰

看到Discuz是2个下拉列表进行合并的，网上找了一些资料，然后写了这个小源码，在这里和大家分享一下！
运行效果图，如下所示（深黑的地方选不中，因为那是上一级的分类）：

项目结构图如下所示：

Controls类库SmartDropDownList.cs代码如下所示：

SmartDropDownList.cs

复制代码代码如下:

 
using System; 
2 using System.Collections.Generic; 
3 using System.Linq; 
4 using System.Text; 
5 using System.Web.UI.WebControls; 
6 using System.Web.UI; 
7 using System.ComponentModel; 
8 using System.Web; 
9 
namespace mydream.Controls 
{ 
[ToolboxData("<{0}:SmartDropDownList runat=server></{0}:SmartDropDownList>")] 
public class SmartDropDownList : DropDownList 
{ 
/// <summary> 
/// 构造函数 
/// </summary> 
public SmartDropDownList() { } 
/// <summary> 
/// 将控件的内容呈现到指定的编写器中 
/// </summary> 
/// <param name="writer"></param> 
protected override void RenderContents(HtmlTextWriter writer) 
{ 
OptionGroupRenderContents(writer); 
} 
/// <summary> 
/// 呈现Option或OptionGroup 
/// </summary> 
/// <param name="writer">writer</param> 
private void OptionGroupRenderContents(HtmlTextWriter writer) 
{ 
// 是否需要呈现OptionGroup的EndTag 
bool writerEndTag = false; 
foreach (ListItem li in this.Items) 
{ 
// 如果没有optgroup属性则呈现Option 
if (li.Value != this.OptionGroupValue) 
{ 
// 呈现Option 
RenderListItem(li, writer); 
} 
// 如果有optgroup属性则呈现OptionGroup 
else 
{ 
if (writerEndTag) 
// 呈现OptionGroup的EndTag 
OptionGroupEndTag(writer); 
else 
writerEndTag = true; 
// 呈现OptionGroup的BeginTag 
OptionGroupBeginTag(li, writer); 
} 
} 
if (writerEndTag) 
// 呈现OptionGroup的EndTag 
OptionGroupEndTag(writer); 
} 
/// <summary> 
/// 呈现OptionGroup的BeginTag 
/// </summary> 
/// <param name="li">OptionGroup数据项</param> 
/// <param name="writer">writer</param> 
private void OptionGroupBeginTag(ListItem li, HtmlTextWriter writer) 
{ 
writer.WriteBeginTag("optgroup"); 
// 写入OptionGroup的label 
writer.WriteAttribute("label", li.Text); 
foreach (string key in li.Attributes.Keys) 
{ 
// 写入OptionGroup的其它属性 
writer.WriteAttribute(key, li.Attributes[key]); 
} 
writer.Write(HtmlTextWriter.TagRightChar); 
writer.WriteLine(); 
} 
/// <summary> 
/// 呈现OptionGroup的EndTag 
/// </summary> 
/// <param name="writer">writer</param> 
private void OptionGroupEndTag(HtmlTextWriter writer) 
{ 
writer.WriteEndTag("optgroup"); 
writer.WriteLine(); 
} 
/// <summary> 
/// 呈现Option 
/// </summary> 
/// <param name="li">Option数据项</param> 
/// <param name="writer">writer</param> 
private void RenderListItem(ListItem li, HtmlTextWriter writer) 
{ 
writer.WriteBeginTag("option"); 
// 写入Option的Value 
writer.WriteAttribute("value", li.Value, true); 
if (li.Selected) 
{ 
// 如果该Option被选中则写入selected 
writer.WriteAttribute("selected", "selected", false); 
} 
foreach (string key in li.Attributes.Keys) 
{ 
// 写入Option的其它属性 
writer.WriteAttribute(key, li.Attributes[key]); 
} 
writer.Write(HtmlTextWriter.TagRightChar); 
// 写入Option的Text 
HttpUtility.HtmlEncode(li.Text, writer); 
writer.WriteEndTag("option"); 
writer.WriteLine(); 
} 
/// <summary> 
/// 用于添加SmartDropDownList的分组项的ListItem的Value值 
/// </summary> 
[ 
Browsable(true), 
Description("用于添加DropDownList的分组项的ListItem的Value值"), 
Category("扩展") 
] 
public virtual string OptionGroupValue 
{ 
get 
{ 
string s = (string)ViewState["OptionGroupValue"]; 
return (s == null) ? "optgroup" : s; 
} 
set 
{ 
ViewState["OptionGroupValue"] = value; 
} 
} 
} 
} 

smartDropDownList.aspx页面代码如下所示：
smartDropDownList.aspx

复制代码代码如下:

 
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="smartDropDownList.aspx.cs" Inherits="smartDropDownList" %> 
<%@ Register Assembly="Controls" Namespace="mydream.Controls" TagPrefix="cc1" %> 
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 
<html xmlns="http://www.w3.org/1999/xhtml"> 
<head runat="server"> 
<title></title> 
</head> 
<body> 
<form id="form1" runat="server"> 
<div> 
<cc1:SmartDropDownList ID="SmartDropDownList1" runat="server"> 
</cc1:SmartDropDownList> 
</div> 
</form> 
</body> 
</html> 

smartDropDownList.aspx页面smartDropDownList.cs如下所示：
smartDropDownList.cs

复制代码代码如下:

 
using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Web; 
using System.Web.UI; 
using System.Web.UI.WebControls; 
using System.Data; 
public partial class smartDropDownList : System.Web.UI.Page 
{ 
protected void Page_Load(object sender, EventArgs e) 
{ 
if (!IsPostBack) 
{ 
this.Bindddlist(this.SmartDropDownList1); 
} 
} 
/// <summary> 
/// 板块ListItem 
/// </summary> 
/// <returns></returns> 
private List<ListItem> GetBoardList() 
{ 
List<ListItem> list = new List<ListItem>(); 
for (int i = 1; i < 6; i++) 
{ 
ListItem li = new ListItem("这里是板块"+i,i.ToString()); 
list.Add(li); 
} 
return list; 
} 
/// <summary> 
/// 子板块ListItem 
/// </summary> 
/// <returns></returns> 
private List<ListItem> GetSubBoardList() 
{ 
List<ListItem> list=this.GetBoardList(); 
List<ListItem> list_sub = new List<ListItem>(); 
foreach (ListItem li in list) 
{ 
ListItem li_sub = new ListItem("这一项是上一级的子板块", "这里是你像传递参数的值"); 
list_sub.Add(li_sub); 
} 
return list_sub; 
} 
/// <summary> 
/// 绑定下拉控件数据 
/// </summary> 
private void Bindddlist(mydream.Controls.SmartDropDownList smartddlist) 
{ 
smartddlist.Items.Clear(); 
List<ListItem> list = this.GetBoardList(); 
foreach (ListItem li in list) 
{ 
ListItem item = new ListItem("--" + li.Text, "optgroup"); 
smartddlist.Items.Add(item); 
List<ListItem> list_sub = this.GetSubBoardList(); 
foreach (ListItem li_sub in list_sub) 
{ 
smartddlist.Items.Add(li_sub); 
} 
} 
smartddlist.DataBind(); 
} 
} 

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