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 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...
• Dude, Where's my Folder treeview?! After a wee bit O' overzealous registry cleaning last week, I had a minor panic. Well, a picture being worth a 1000 words, here's what I saw when I opened...
• 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...
• 10 Useful, Often Overlooked HTML Tags. Pop quiz: When would you use the <wbr> tag, and what does it do? Yeah, I had no idea either. In fact, I had never even seen this tag before,...

• Critique Groups Develop Writers Critique groups help aspiring writers improve their work while networking with writers of similar passions.  It’s a little jarring to hear others’ criticism but that’s only because we think of criticism as a purely negative diatribe given by high-brow experts. Try to remember that the members of successful critique groups......
• Internet Marketing Needs a Makeover? Let me start by saying: and a Major One at that! Last time I checked:  we are in the 21st century, so how come Internet marketers are still stuck in the yesteryears? Allow me to count the ways:     HTML Your Basic HTML is still the foundation and serves......
• Getting Started Writing Articles The job of article writing requires considerable skill and expertise in order to carry out with ease and perfection. Yes, this job is not as easy as many would think. An article is written in order to provide some information and it is very important that the article writer......
• 10 Step Web Design and Development Contract Agreement This can be not written by a skilled lawyer or anyone shut to one. It is written by a usually business owner of a successful internet development company who has no law degree or the budget to rent a lawyer to write a net development contract. However, they're in want......
• Important Reasons For Submitting Articles Article directories are important to many web site owners all over the world. Many of them submit large numbers of articles to article directories on regular basis. No matter what type of business you have, you probably get a lot of things to share with your readers. Writing and submitting......