Jelle Druyts

A lot of ASP.NET WebControls use a url, such as the NavigateUrl property of the HyperLink control or the ImageUrl for an Image. If you set such a url to a relative path, you might experience some unexpected behaviour in some more advanced scenarios - unfortunately without a clean workaround.

Internally these url's are rendered to html using the Control.ResolveUrl method. The first thing this does is deciding whether or not it's a relative url. If it's not, then the url is just returned so absolute url's remain untouched. If it is a relative url, then it is prefixed with the control's TemplateSourceDirectory - and there's the tricky part. The Control.TemplateSourceDirectory property is "the virtual directory of the page or user control that contains the server control". This means that a relative url is always relative to the containing control's directory, not to where you're setting it from. If you remember my post on ASP.NET Path Discovery, this will sound familiar. More on that later.

Now imagine a scenario where you have a breadcrumb-style header control (Header.ascx) with some navigational hyperlinks on it that need to be added depending on the page hosting the control. This means the hyperlink controls are contained in Header.ascx, and their url's will always be relative to this control's directory. If you use the header control from various places in various directories then you need to step away from the idea that setting these url's will be relative to the page you're working in. In stead you should always think on how to get from the header control to the current page's directory which is a pretty heavy burden. And as I mentioned in my post on ASP.NET Path Discovery there is no clean out-of-the-box way to discover this 'current path'.

As for a workaround: there is no property on a hyperlink or any other control that allows you to modify this behaviour and take the url you gave it as such without modifying the path. The only thing you can do is to manually set the href attribute in stead of using the NavigateUrl property as such: myHyperLink.Attributes["href"] = myUrl. I probably don't need to mention that this isn't my idea of clean code but sometimes you just need to get your work done too