I’ve been writing a subclass of the MS Webcontrol.TreeView control for one of our Web Applications at work. I figured this would be a fairly easy task, since I only needed to extended it with a few properties. It turns out that I was caught on a nit-picky annoyance in the TreeView control itself.

The TreeView control renders verticals lines with gaps.

Here’s a screen cap of the problem.

As you can see, the TreeView control renders the vertical line with a gap, or break (looks like a dashed line!). It didn’t matter how I loaded the data - dynamic/runtime/design time - I get the same gap no matter what!

I was able to see that it was not a problem in IE 6 or less, but what good is that? Well, it turns out that it was a bit of a clue because starting with version 5, IE didn’t render things correctly per the CSS boxing specification. This was fixed in IE 7, but to provide backwards compatibility, Microsoft carried this busted form of rendering forward in IE 6 as QuirksMode. The line gap problem only occurs in strict mode (default for IE 7 and 8, as well as firefox). I could make the line gap go away by forcing the browser into QuirksMode (by adding a comment, ex:

< ! - - QUIRK! - - >

to the very top of the HTML file), but I was writing a web control and would not always have the luxury of controlling my container.

I needed to find a long term solution to this problem.

Next, I looked at the HTML source of the rendered page, and saw this:

[html]
<table cellpadding="0" cellspacing="0" style="border-width:0;">
<tr>
<td>
<div style="width:20px;height:1px">
<img src="/TreeviewControlTest/WebResource.axd?d=OYmDnVppVECKIpxOWC8o8Y7DO6QwB2J3EY4s4RR8zAU1&amp;t=633765128008804061" alt="">
</div>
</td>
<td>
<img src="/TreeviewControlTest/WebResource.axd?d=OYmDnVppVECKIpxOWC8o8UGy0bLoCc8gOB1oQm6Pzj81&amp;t=633765128008804061" alt="">
</td>
<td class="TreeView1_WebTree_1" style="white-space:nowrap;">
<a class="TreeView1_WebTree_0" href="javascript:__doPostBack(’TreeView1$WebTree’,'Root//Tree’)" onclick="TreeView_SelectNode(TreeView1_WebTree_Data, this,’TreeView1_WebTreet6′);" id="TreeView1_WebTreet6" name="TreeView1_WebTreet6">Tree</a>
</td>
</tr>
</table>
[/html]

Each node is rendered as a table, with the vertical line and expand/collapse icons being in their own table cell and wrapped in a div. The problem was the style applied to the outer div - style=”width:20px;height:1px“.

That 1px height was causing the vertical line image to be compressed, but where did it come from?

Reflecting on System.Web.UI.WebControls.TreeNode

I spent almost an hour delving into the various (and copious!) style properties for the tree and its nodes, looking for where this height setting was generating from. I couldn’t find it! I eventually opened the System.Web.UI.WebControls.dll in Reflector to see what the render code for the node was doing:

Well, once I saw that the code was hard-wired to render this CSS style, I was done. Or was I?

!important

Well, it wasn’t going to be as easy as setting the style in the code behind, but I could override the style in my own class.

The trick is to define, and apply the following CSS class:

[css]
<style type="text/css">
.MyTreeView TD Div
{
height: 20px!important;
}
</style>
[/css]

The !important CSS directive overrides the style applied in the System.Web.UI.WebControls.TreeNode render method.

Again, just as with the QuirksMode comment above, I was able to add the CSS style to the page and voila - problem solved. But this still wasn’t good enough. I needed this to work out of the box for any consumers of my control.

The ultimate answer was to override the RenderBeginTag of the TreeView control, and render this style before the control itself:

[vb language=".net"]

Public Overrides Sub RenderBeginTag(ByVal writer As System.Web.UI.HtmlTextWriter)
‘/////////////////////////////////////////////////////////////////////////////////////////
‘/// This is a total hack to get around some Microsoft BS which hardwires
‘/// a style attribute on the node div to set the height = 1px!
‘///
‘/// This renders a css override to force the div to the proper height
‘/////////
Me.CssClass = String.Concat(Me.CssClass, " MyTreeView")
writer.WriteBeginTag(HtmlTextWriterTag.Style.ToString)
writer.WriteAttribute(HtmlTextWriterAttribute.Type.ToString, "text/css")
writer.WriteLine(HtmlTextWriter.TagRightChar)
writer.Write(".MyTreeView TD Div ")
writer.WriteLine("{ height: 20px!important; }")
writer.WriteEndTag(HtmlTextWriterTag.Style.ToString)
writer.WriteLine()
‘//////////////////////////////////////////////////

‘/// Render the Standard Begin Tag
MyBase.RenderBeginTag(writer)
End Sub
[/vb]

• Free Firewall Recommendations (Protect Yourself Online With These Free Firewalls) If your home computer is connected to the internet, or to other computers that are connected to the internet - you need a firewall. It's as simple as that. Hackers...
• How To Control Disk Thrash From ccmexec.exe (SMS Agent). Today started like any other day at work. I sat down, logged into my PC and was greeted by the thrashing sound of my hard drive. I've come to realize...
• The 3 Most Important Questions You Should Ask About Each Bug You Find. I stumbled upon (quite literally) an article by Tom Van Vleck titled Three Questions About Each Bug You Find today, and thought I would share it: "The key idea behind...
• How to find what's running under SVCHost.exe My PC was behaving sluggishly the other day. I tried to be patient, but had to fire up the task manager when I could bear it no longer. That's when...
• How to Delete Empty Folders - FREE! While performing a disk cleanup recently, I had cause to locate and delete any empty folders under a root folder. I knew there had to be a batch file command...

• Web Marketing Business Solutions For Small Business | Online Marketing Consultant Web MarketingLooking for ways to give your business a marketing boost? If so, do you own an on-line presence as part of your promotions formula? The World Wide Web is now the first selection for individuals researching products and services they are thinking buying.The web has now assumed dominance the......
• Create your web page with NetBeans - Part 3 In this part we will look into PHP basics PHP is a widely used open source, general-purpose scripting language. It was originally designed for use in Web site development.  PHP proved so useful and popular, it rapidly grew to become the full-featured language that it is today, acquiring the name......
• Musical Instruments: Drums for Sale The unique thing about drums when it comes to making music is that there are so many different elements that change the sound you create when you play them. The size, shape and composition of the drum will all alter the sound that it creates. Whether you beat on the......
• Visual Quickstart Guide - HTML, XHTML & CSS 6th Edition I recently bought the book Visual Quickstart Guide - HTML, XHTML & CSS 6th Edition to refresh my knowledge on Web creation and to serve as a handy reference for me. I know that there are a lot of free XHTML + CSS tutorials online but nothing beats a......
• Dedicated Server Hosting Advantages Dedicated Web Hosting Has Many Advantages By Volodymyr Zablotskyy Compared to shared web hosting, it is more expensive to host your web site on a dedicated server. You may wonder why you would even think about using a dedicated web hosting solution. Well, there are many advantages to having your......