Why can't I set the listbox selectedIndex to -1?

[amtamayo]

I have a simple webform that has a listbox that I bind to a dataview
at designtime. This provides an optional selection for the user so I
wanted to have no default value selected. So on the Page_Load event,
I set the selectedIndex to -1. However, when I run the page, the
default value is still 0, which forces the first item to be
automatically selected. I tried a bunch of things. I tried setting
it to 0, then -1. I tried to call ClearSelection() then set it to -1,
but no avail. This is a listbox, for crying out loud! This ought to
be simple, but is not.

Need help.

 

[Ray Costanzo]

This is just how most (all maybe?) browsers work. If you create a static
html file and put a <select> in it with some options, the first one is
selected by default in every browser I've used. According to W3C, this is
up to the browser to determine what the right thing to do is.
http://www.w3.org/TR/html4/interact/forms.html#h-17.6 "If no OPTION element
has the selected attribute set, user agent behavior for choosing which
option is initially selected is undefined."

Perhaps this will be a satisfactory option:

<aspropDownList ID="ddl" runat="server" DataValueField="ID"
DataTextField="Display" AppendDataBoundItems="true">
<asp:ListItem Value="">Select an option</asp:ListItem>
</aspropDownList>

Note the AppendDataBoundItems attribute.

Ray at work

 

[bruce barker]

this can only be done in javascript. in html if you render a select with
no option set as selected, it defaults to the first. in javascript you
can set the selectedIndex to -1 which will unselect.

you can subclass the listbox, and have it generate the required javascript.

-- bruce (sqlwork.com)