The Attributes property of a ListItem control only works within an HtmlSelect control


When you use the RadioButton or DropDownList control, if you try to place a key-value pair in the ListItem control, the key-value pairs are not written to the result page.

For example, the following RadioButtonList code

<asp:RadioButtonList id="RadioButtonList1" runat="server">
<asp:ListItem Value="v1" Key="k1">1</asp:ListItem>
RadioButtonList1.Items[0].Attributes.Add("key", "k1");
only returns the following output:

<input id="RadioButtonList1_0" type="radio" name="RadioButtonList1" value="v1" />
<label for="RadioButtonList1_0">1</label>
Similarly, the following DropDownList code

<asp:DropDownList id="DropDownList1" runat="server">
<asp:ListItem Value="v1" Key="k1">1</asp:ListItem>
only returns the following output:

<option value=v1>1</option>

The "Key=k1" is not rendered.


The ListItem control has a property Attributes of type AttributeCollection. When the ListItem control is inside a RadioButtonList control or a DropDownList control, key-value pairs that you assign to the Attributes property of the ListItem control (either programmatically or declaratively) are not rendered.


To work around this problem in the RadioButtonList control, use a group of HtmlInputRadioButton controls. For example:

<input id="Radio01" type="radio" name="group1" Key="k1" runat="server" >
To work around this problem in the DropDownList control, use the HtmlSelect control. For example:
<select runat="server">
<option value="v1" id="ID1" key="k1">1</option>


This behavior is by design.

More Information

In the "Resolution" section of this article, the HtmlSelect control was used to show how to implement expando attributes as a workaround for using the DropDownList control. While both classes do make use of the ListItem class internally, they support expando attributes differently. The HtmlSelect control does support using expando attributes because its programming model is more HTML-centric. However, supporting expando attributes with the DropDownList control is more involved than just rendering the attributes themselves. For example, you cannot use data-binding to support attributes with the DropDownList control.

Article ID: 309338 - Last Review: Mar 24, 2009 - Revision: 1