I've used the standard control in the past, and just added a simple ControlAdapter for it that would override the default behavior so it could render <optgroup>s in certain places. This works great even if you have controls that don't need the special behavior, because the additional feature doesn't get in the way.
请注意,这是为特定目的编写的,并且是用.NET2.0编写的,因此它可能不太适合您,但至少应该给您一个起点.此外,您还必须在项目中使用.browserfile将其挂钩(有关示例,请参阅本文末尾的示例).
'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
下面是同一类的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",如下所示:
<!--
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>