I was working on a site tonight after being away from it for over three months. I came across some CSS and it took me a while to remember what it was for. I gleaned this online somewhere ages ago, but kudos and credit to the author whoever they are!

For some time I have been having problems using the ASP.NET TreeView control in Sitemaps; every time I would hover over one of the parent nodes it would jump up and down. Here's some sample markup and the CSS to fix it in Firefox:

        <div id="idTreeView">
            <asp:TreeView ID="TreeView1" runat="server"                     DataSourceID="SiteMapDataSource1"
                    HoverNodeStyle-Height="0" Font-Bold="true" ImageSet="BulletedList">
                <RootNodeStyle Font-Bold="True" />
                <ParentNodeStyle VerticalPadding="0px" Font-Bold="True"                     Font-Underline="false"  />
                <HoverNodeStyle Font-Underline="false" ForeColor="#5555DD" />
                <NodeStyle Font-Bold="False" Font-Size="8pt" CssClass="sitelink"
                    ForeColor="Black" HorizontalPadding="5px" NodeSpacing="0px"                     VerticalPadding="0px" />
            </asp:TreeView>
           
            <asp:SiteMapDataSource ID="SiteMapDataSource1" runat="server" />
        </div>

        div#idTreeView img
        {
            display: block;
            float: left;
        }

        div#idTreeView div
        {
            display: inline-block;
        }

        div#idTreeView .sitelink a
        {
            text-decoration:none;
        }

C# 4.0 is the next version of the C# language being shipped with VS 2010. Personally, I'm still coming to terms with Generics as introduced in C# 2.0 and LINQ which came with 3.0. Anders Hejlsberg touched on the Covariance/Contravariance topic in his TechEd presentation in LA last month entitled "The Future of C#".

The terms Invariance, Covariance and Contravariance are not by any means new. Anyone coming from a computer science background will have encountered the terms. Prior to attending Anders' session, I hadn't given this much conscious thought in a long time - we tend to know what we can and can't do within the syntactical constraints of a language - and tend not to question things further. However, in C# 4.0, delegates and interfaces will play nicer when working with generics. So much attention is likely to be focused on the dynamic programming additions in C# 4.0 (mainly in support of LINQ), that this addition may go unnoticed.

Terminology:

Invariant: A return parameter is invariant if we must use the exact match of the type name. In other words, neither covariance nor contravariance is permitted

Covariant: A parameter is covariant if we can use a more derived type as a substitute for the parameter type. In other words, a subclass instance can be used where a parent class instance was expected.

Contravariant: A return value is contravariant if we can assign the return type to a variable of a less derived type than the parameter. In other words, a super class instance can be used where a subclass instance was expected.

Generally, C# supports covariant parameters and contravariant return types. There has always been support for covariance and contravariance in C# - C# 4.0 will just ensure that generic delegates and interfaces will also behave they way we would expect.

Eric Lippert is the developer responsible for this feature of the C# 4.0 release and has an eleven-part blog series on just this topic. I would also recommend reading Charlie Calvert's article on this topic for some code samples.

Side Note: You do not need VS 2010 to experiment with these features - just download the framework to a test VM.

There are times when you will want to set the color of the grid lines in your GridView - however there is not to my knowledge a way of doing this declaratively. A workaround is to do this by tapping into the GridView's RowDataBound event.

First, set the OnRowDataBound property in the markup of the GridView:

OnRowDataBound="MyGrid_RowDataBound"

Second, set the color in the OnRowDataBound handler method:

protected void MyGrid_RowDataBound(object sender, GridViewRowEventArgs e)
{
     foreach (TableCell tc in e.Row.Cells)
     {
         tc.Attributes["style"] = "border-color: #c3cecc";
     }
}

Happy coding :-)

Update 06-01-2009:
See Lee's suggestion in the comments on a quicker way to do this:
Add this to the page Load method: this.GridView1.Attributes.Add("bordercolor", "c3cecc");