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>
</asp:RadioButtonList>
-or-
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>
</asp:DropDownList>
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>
</select>
This behavior is by design.
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.