使用<optgroup>的asp.net（webforms）的Dropdownlist控件？

Question

谁能为asp.net（3.5）推荐一个可以呈现选项组的下拉列表控件？谢谢

Answer 1

我过去使用过标准控件，只是为其添加了一个简单的ControlAdapter，它将覆盖默认行为，因此它可以在某些位置呈现<optgroup>。即使您的控件不需要特殊的行为，这也能很好地工作，因为附加功能不会妨碍您。

请注意，这是出于特定目的并用.Net 2.0编写，因此它可能也不适合您，但至少应为您提供一个起点。另外，您还必须在项目中使用.browserfile进行连接（示例请参见文章末尾）。

'This codes makes the dropdownlist control recognize items with "--"

'for the label or items with an OptionGroup attribute and render them

'as <optgroup> instead of <option>.

Public Class DropDownListAdapter

    Inherits System.Web.UI.WebControls.Adapters.WebControlAdapter

    Protected Overrides Sub RenderContents(ByVal writer As HtmlTextWriter)

        Dim list As DropDownList = Me.Control

        Dim currentOptionGroup As String

        Dim renderedOptionGroups As New Generic.List(Of String)

        For Each item As ListItem In list.Items

            Page.ClientScript.RegisterForEventValidation(list.UniqueID, item.Value)

            If item.Attributes("OptionGroup") IsNot Nothing Then

                'The item is part of an option group

                currentOptionGroup = item.Attributes("OptionGroup")

                If Not renderedOptionGroups.Contains(currentOptionGroup) Then

                    'the header was not written- do that first

                    'TODO: make this stack-based, so the same option group can be used more than once in longer select element (check the most-recent stack item instead of anything in the list)

                    If (renderedOptionGroups.Count > 0) Then

                        RenderOptionGroupEndTag(writer) 'need to close previous group

                    End If

                    RenderOptionGroupBeginTag(currentOptionGroup, writer)

                    renderedOptionGroups.Add(currentOptionGroup)

                End If

                RenderListItem(item, writer)

            ElseIf item.Text = "--" Then 'simple separator

                RenderOptionGroupBeginTag("--", writer)

                RenderOptionGroupEndTag(writer)

            Else

                'default behavior: render the list item as normal

                RenderListItem(item, writer)

            End If

        Next item

        If renderedOptionGroups.Count > 0 Then

            RenderOptionGroupEndTag(writer)

        End If

    End Sub

    Private Sub RenderOptionGroupBeginTag(ByVal name As String, ByVal writer As HtmlTextWriter)

        writer.WriteBeginTag("optgroup")

        writer.WriteAttribute("label", name)

        writer.Write(HtmlTextWriter.TagRightChar)

        writer.WriteLine()

    End Sub

    Private Sub RenderOptionGroupEndTag(ByVal writer As HtmlTextWriter)

        writer.WriteEndTag("optgroup")

        writer.WriteLine()

    End Sub

    Private Sub RenderListItem(ByVal item As ListItem, ByVal writer As HtmlTextWriter)

        writer.WriteBeginTag("option")

        writer.WriteAttribute("value", item.Value, True)

        If item.Selected Then

            writer.WriteAttribute("selected", "selected", False)

        End If

        For Each key As String In item.Attributes.Keys

            writer.WriteAttribute(key, item.Attributes(key))

        Next key

        writer.Write(HtmlTextWriter.TagRightChar)

        HttpUtility.HtmlEncode(item.Text, writer)

        writer.WriteEndTag("option")

        writer.WriteLine()

    End Sub

End Class

这是同一类的C＃实现：

/* This codes makes the dropdownlist control recognize items with "--"

 * for the label or items with an OptionGroup attribute and render them

 * as <optgroup> instead of <option>.

 */

public class DropDownListAdapter : WebControlAdapter

{

    protected override void RenderContents(HtmlTextWriter writer)

    {

        //System.Web.HttpContext.Current.Response.Write("here");

        var list = (DropDownList)this.Control;

        string currentOptionGroup;

        var renderedOptionGroups = new List<string>();

        foreach (ListItem item in list.Items)

        {

            Page.ClientScript.RegisterForEventValidation(list.UniqueID, item.Value);

            //Is the item part of an option group?

            if (item.Attributes["OptionGroup"] != null)

            {

                currentOptionGroup = item.Attributes["OptionGroup"];

                //Was the option header already written, then just render the list item

                if (renderedOptionGroups.Contains(currentOptionGroup))

                    RenderListItem(item, writer);

                //The header was not written,do that first

                else

                {

                    //Close previous group

                    if (renderedOptionGroups.Count > 0)

                        RenderOptionGroupEndTag(writer);

                    RenderOptionGroupBeginTag(currentOptionGroup, writer);

                    renderedOptionGroups.Add(currentOptionGroup);

                    RenderListItem(item, writer);

                }

            }

            //Simple separator

            else if (item.Text == "--")

            {

                RenderOptionGroupBeginTag("--", writer);

                RenderOptionGroupEndTag(writer);

            }

            //Default behavior, render the list item as normal

            else

                RenderListItem(item, writer);

        }

        if (renderedOptionGroups.Count > 0)

            RenderOptionGroupEndTag(writer);

    }

    private void RenderOptionGroupBeginTag(string name, HtmlTextWriter writer)

    {

        writer.WriteBeginTag("optgroup");

        writer.WriteAttribute("label", name);

        writer.Write(HtmlTextWriter.TagRightChar);

        writer.WriteLine();

    }

    private void RenderOptionGroupEndTag(HtmlTextWriter writer)

    {

        writer.WriteEndTag("optgroup");

        writer.WriteLine();

    }

    private void RenderListItem(ListItem item, HtmlTextWriter writer)

    {

        writer.WriteBeginTag("option");

        writer.WriteAttribute("value", item.Value, true);

        if (item.Selected)

            writer.WriteAttribute("selected", "selected", false);

        foreach (string key in item.Attributes.Keys)

            writer.WriteAttribute(key, item.Attributes[key]);

        writer.Write(HtmlTextWriter.TagRightChar);

        HttpUtility.HtmlEncode(item.Text, writer);

        writer.WriteEndTag("option");

        writer.WriteLine();

    }

}

我的浏览器文件名为“ App_Browsers \ BrowserFile.browser”，看起来像这样：

<!--

    You can find existing browser definitions at

    <windir>\Microsoft.NET\Framework\<ver>\CONFIG\Browsers

-->

<browsers>

   <browser refID="Default">

      <controlAdapters>

        <adapter controlType="System.Web.UI.WebControls.DropDownList" 

               adapterType="DropDownListAdapter" />

      </controlAdapters>

   </browser>

</browsers>

Answer 2

我使用JQuery来完成此任务。我首先为ListItem后端的每个对象添加了一个新属性，然后在JQuery wrapAll()方法中使用该属性来创建组...

C＃：

foreach (ListItem item in ((DropDownList)sender).Items)

{

    if (System.Int32.Parse(item.Value) < 5)

        item.Attributes.Add("classification", "LessThanFive");

    else

        item.Attributes.Add("classification", "GreaterThanFive");

} 

jQuery的：

$(document).ready(function() {

    //Create groups for dropdown list

    $("select.listsmall option[@classification='LessThanFive']")

        .wrapAll("&lt;optgroup label='Less than five'&gt;");

    $("select.listsmall option[@classification='GreaterThanFive']")

        .wrapAll("&lt;optgroup label='Greater than five'&gt;"); 

});

Answer 3

这里是C＃版本：

using System;

using System.Web.UI.WebControls.Adapters;

using System.Web.UI;

using System.Web.UI.WebControls;

using System.Collections.Generic;

using System.Web;

//This codes makes the dropdownlist control recognize items with "--"'

//for the label or items with an OptionGroup attribute and render them'

//as  instead of .'

public class DropDownListAdapter : WebControlAdapter

{

    protected override void RenderContents(HtmlTextWriter writer)

    {

        DropDownList list = Control as DropDownList;

        string currentOptionGroup;

        List renderedOptionGroups = new List();

        foreach(ListItem item in list.Items)

        {

            if (item.Attributes["OptionGroup"] != null)

            {

                //'The item is part of an option group'

                currentOptionGroup = item.Attributes["OptionGroup"];

                //'the option header was already written, just render the list item'

                if(renderedOptionGroups.Contains(currentOptionGroup))

                    RenderListItem(item, writer);

                else

                {

                    //the header was not written- do that first'

                    if (renderedOptionGroups.Count > 0)

                        RenderOptionGroupEndTag(writer); //'need to close previous group'

                    RenderOptionGroupBeginTag(currentOptionGroup, writer);

                    renderedOptionGroups.Add(currentOptionGroup);

                    RenderListItem(item, writer);

                }

            }

            else if (item.Text == "--") //simple separator

            {

                RenderOptionGroupBeginTag("--", writer);

                RenderOptionGroupEndTag(writer);

            }

            else

            {

                //default behavior: render the list item as normal'

                RenderListItem(item, writer);

            }

        }

        if(renderedOptionGroups.Count > 0)

            RenderOptionGroupEndTag(writer);

    }

    private void RenderOptionGroupBeginTag(string name, HtmlTextWriter writer)

    {

        writer.WriteBeginTag("optgroup");

        writer.WriteAttribute("label", name);

        writer.Write(HtmlTextWriter.TagRightChar);

        writer.WriteLine();

    }

    private void RenderOptionGroupEndTag(HtmlTextWriter writer)

    {

        writer.WriteEndTag("optgroup");

        writer.WriteLine();

    }

    private void RenderListItem(ListItem item, HtmlTextWriter writer)

    {

        writer.WriteBeginTag("option");

        writer.WriteAttribute("value", item.Value, true);

        if (item.Selected)

            writer.WriteAttribute("selected", "selected", false);

        foreach (string key in item.Attributes.Keys)

            writer.WriteAttribute(key, item.Attributes[key]);

        writer.Write(HtmlTextWriter.TagRightChar);

        HttpUtility.HtmlEncode(item.Text, writer);

        writer.WriteEndTag("option");

        writer.WriteLine();

    }

}