Depends. Where is your TextBox? Try putting your textbox in update panel. And also, I can't find
AutoPostBack="true"
property of your dropdownlist. Try adding that.
Try like this:
HTML:
<asp:updatepanel id="UpdatePanel1" runat="server" xmlns:asp="#unknown">
<contenttemplate>
<asp:dropdownlist id="DropDownList1" runat="server">
onselectedindexchanged="DL1_SelectedIndexChanged" AutoPostBack="true">
<asp:listitem></asp:listitem>
<asp:listitem>Others</asp:listitem>
</asp:dropdownlist>
<asp:textbox id="TextBox1" runat="server" visible="false">
</asp:textbox></contenttemplate>
</asp:updatepanel>
Code Behind:
Protected Sub DL1_SelectedIndexChanged(sender As Object, e As EventArgs)
If DropDownList1.SelectedItem.Text = "Others" Then
TextBox1.Visible = True
Else
TextBox1.Visible= False
End If
End Sub
--Amit