Customizing “lookful” WPF controls – Take 2

Last week I posted a technique for customizing controls in WPF that don’t offer a replaceable ControlTemplate – I described them as “lookful” controls because their behavior and appearance are tied in with their functionality. My approach involved creating a custom control that derives from the one being targeted. That solution has some significant downsides, though, including that if the control is part of another (composition) then you have to modify the parent control to tell it to use your new custom control as a child – it works in most cases, it’s just not ideal. I figured someone might call me out on it eventually and, sure enough, the day I posted it fellow WPF’er “John” ruminated in a comment about using attached properties to accomplish the task instead. That got my wheels turning and I decided to put together a solution that, frankly, doesn’t stink…

Showing ToolTips on a trimmed TextBlock (WPF)

[UPDATE: This solution has been superceded by a much better implementation in this later post.]

I recently downloaded the WPF Toolkit for which Microsoft posted the first DataGrid CTP. That DataGrid is their attempt at responding to what is likely one of the most requested missing features in WPF. Many people have suggested that WPF doesn’t need a DataGrid and may be better off not to provide one, but I and others disagree – we do need a DataGrid, but it must be lookless! Anyway, I’m getting off topic.

While I really appreciate the work that went into building such a flexible and feature-packed control, I was quickly disheartened to learn that it has no mechanism built in to handle the scenario where column data (text) gets cut off due to size constraints. Actually there is one means, wrapping the text, but for the task I’m currently working on wrapping is really not an acceptable approach.

Customizing “lookful” WPF controls

[UPDATE: This solution has been superceded by a much better implementation in this later post.]

If you’ve spent any time reading material about WPF, it’s inevitable that the term “lookless” has come up at least once. Ironically, that’s not actually a word, at least not according to Webster. However, the term has been drilled into the minds of WPF developers the world over and will likely be added to the Windows dictionary at some point. Microsoft even used the word several times in this patent application which describes in precise detail what it means. In case the practical meaning isn’t clear, in essence “lookless” equates to “has a flexible UI”. In other words, lookless controls are focused on functionality, not appearance or even visual behavior. Of course most controls do have a default appearance, but lookless controls are, by nature, almost completely customizable (limited mostly by imagination and time.)

Matt Duffin of the UK even suggested we all grab a pen and write “All controls in WPF should be lookless” over and over until it becomes ingrained. Not sure I would go that far, but clearly the overwhelming guidance for WPF designers is that most controls should have a stylable and/or templatable appearance which is independent of functionality. Being aware of that guidance just makes it even more frustrating when you run into a control built into the framework which violates that tenet.

The particular control I’m referring to in this case is the TextBlock. Recently I had a desire to enable ToolTips on a TextBlock when (and only when) its text is being trimmed. I’ve written a separate post which goes into the solution to that specific problem in more depth, but getting there required a lot of foundational work which can be applied to address any number of issues.