Here’s one of those things I’m always forgetting, and since most of my work is on-site at clients, I don’t have a large source code repository to go back to reference.

To correctly reference a style sheet from within a master page in ASP.NET, use the following:


<link rel="stylesheet" href="<%= ResolveUrl("~/css/screen.css") %>" type="text/css" media="screen, projection" />


It’s the ResolveUrl that does the trick.

At the risk of appearing to be an idiot, I’m going to blog this so I don’t forget. Especially since it bit me twice *in the same project*. Oops.

In .NET 2.0, the old method of getting information from the app.config has been depreciated. The new method is:


ConfigurationManager.ConnectionStrings.Item(YourDB).ConnectionString


For this to work, though, you need to remember to add a reference to System.Configuration. This needs to be done for each project in the solution that uses it. Thankfully I figured out that last bit pretty quickly.

I like to keep a good separation between forms and function in Windows applications I write. So to call a login form, I might call a public function on the login form like: Login.GetLogin(loginName, password).

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I was trying to add yes / no values to three dropdowns on my ASP.NET page. We’re using custom drop down controls, so I needed to add the dropdown items in code behind. Always liking to be efficient in my code and make it pretty, I used this:

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One piece of functionality that is often requested is the ability to submit a web form using the <enter> key. In some cases, you may need multiple textbox controls to submit differently by defaulting to different buttons. In the past there have been various javascript hacks to ensure this works successfully, but in ASP.NET 2.0 there is a simpler function.

By setting the defaultbutton property on a form or – even better – an <ASP:Panel> control, the page automatically handles it for you. Each set of controls which should submit with a certain button can be contained in the panel and everything is hooked up automagically.

One caveat: If you set a default button on a panel but not in the form, other controls seem to use the panel’s default button even when they are not in the panel.

On my client’s project one of my tasks was to write a search engine and corresponding UI screen. The results of the search are displayed using an asp:Repeater control in a pattern similar to Google. One more requirement is a section that pops open to reveal additional, less-frequently-used actions. Sort of a “dropdown” of more options.

I thought I would use a hyperlink with a call to javascript that toggles the display of a <div>. It seemed like the best solution within the context of the existing page.

With that in mind, I added some javascript to my ASP.NET page (using RegisterClientScriptBlock) without a problem. But when it came to adding the “more” link and the show/hide div, I ran into a serious issue.

What I really wanted to do in the repeater’s ItemTemplate was:
<ItemTemplate>
<a href="javascript:toggleDisplay('<%=pnlMoreLinks.ClientID%>');">show / hide</a>
<asp:Panel runat="server" ID="pnlMoreLinks" CssClass="morelinks">
Show and hide me!
</asp:Panel>
<ItemTemplate>

My thought was that it would render code to the browser along the lines of:
<a href="javascript:toggleDisplay( 'ctl00_ContentPage_Repeater_ctl01_pnlMoreLinks');">show / hide</a>
<div id="ctl00_ContentPage_Repeater_ctl01_pnlMoreLinks" class="moreLinks">
Show and hide me!
</div>

The problem is that causes a compile error:
The name 'pnlMoreLinks' does not exist in the current context

Not good. Outside of the repeater, the <%=pnlMoreLinks.ClientID%> works beautifully. Inside the repeater: compile error. It seems the reference to the asp:panel is not available to other controls in the designer. In case you were wondering, proximity had no effect either.

A quick check with the other smart people led to no real epiphanies though the designer. In the end, I manually set the reference in the link to the ClientID of the panel through the ItemDataBound event on the repeater. In the code behind, this method lets you control the formatting of each row as its being rendered. The ClientID of the panel is available at this point of the page’s life cycle.

protected void rptSearchResults_ItemDataBound(object sender, RepeaterItemEventArgs e) {
   HyperLink link = (HyperLink)e.Item.FindControl("lnkMoreLinks");
   Panel panel = (Panel)e.Item.FindControl("pnlMoreLinks");
   if (panel != null && link != null)
      link.NavigateUrl = "javascript:toggleDisplay('" + panel.ClientID + "');";
}

The repeater’s ItemDataBound method has been invaluable to me in a few other tasks… having more control of the repeater than is provided by the designer and data binding is essential to usable, well-built web apps.

And now I have a hide-able div in a repeater control. Sweet.

For some reason I can’t seem to remember this when I need it.

If you have a dropdownlist in ASP.NET:

<asp:dropdownlist id="states" runat="server">

If this dropdownlist is databound:

DataSet ds = new DataSet();
ds.ReadXml(Server.MapPath("states.xml"));
states.DataSource = ds;
states.DataBind();

...and you want to add a blank value to ensure the user has selected a value, do the following:

states.Items.Insert(0,"");

You can substitute any value for the blank string, such as "--select--".