Silverlight Bits&Pieces – Part 9: A MessageBox replacement

OK, let’s put the brand new service provider model to some good use.

Whenever a service call reports an error I want some message box telling me about it (rather than simply swallowing it, which is the default behavior). Whenever the user does something potentially devastating I want some explicit confirmation, read message box, that he knows what he’s doing. MessageBox.Show does all I need (well, it is restricted to OK and OK/Cancel, but one can live with that). Only… these system message boxes are dull, boring, and not at all a shiny example for a Silverlight application. Enter the message box service provider…

Basic implementation of a message box service

The basic implementation will get the infrastructure up and running.

The first step is defining the service contract. Show this and that and a query method. The first (and naive) version looks like this:

The default implementation of our application extension service turned service provider (AES/SP) would use the dull system message boxes to implement that. The code is actually quite straight forward:

Now, I could demand that the app.xaml has this one (or any other service implementing my interface) registered. However, I like to be correct by default, thus my accessor will fall back on this implementation if none is registered – and I can be sure that there will always be a respective service.

All that is left is a search&replace for all calls to MessageBox.Show… E.g. to show an error:

… and to get confirmation, in this case to return a book:

And, of course, it works as expected:

Replacing the Dialog

Second act. Get rid of those dull things.

Create a new “Silverlight Child Window” and style it to look like a message box. I „borrowed“ the images from the Visual Studio Image Library (on my machine under C:\Program Files\Microsoft Visual Studio 9.0\Common7\VS2008ImageLibrary\1033\VS2008ImageLibrary\Objects\png_format\WinVista\) and simply placed all possible images in the dialog. A textbox, two buttons, that’s it. Here is the styled XAML:

Some code is needed for the initialization. The message has to be set, the correct image made visible, etc.. I could probably have done this with less coding, using some tricks and elaborate databinding. But who cares, it’s straight forward and comprehensible (unlike what I probably would have come up with).

Setting the DialogResult property also closes the dialog (sik!).

Finally I need a replacement AES/SP. The main method to show the dialog looks like this:

Great? Great! … GOT YOU! (Fell into the trap myself, actually… )

Fixing the Bug

Remember that in Silverlight everything is asynchronous? Well, everything except MessageBox.Show? And ‘everything’ includes ChildWindow.Show! Meaning my confirm method will not work this way. To overcome this I decided to pass a delegate to the dialog constructor and made sure it’s called in the OK case:

And to be able to pass the delegate I changed the existing AES as well (and the interface respectively):

Of course I had to adjust the default implementation using a messagebox:

The calling code changes respectively, passing a lambda:

Done. Now my application looks nice, even if it has to show a message box:

ANFSCD…

This endeavor served actually three purposes:

• First, I wanted/needed the feature 😉
• Second, I wanted to see/demonstrate the service provider pattern from a user’s point of view.
• And third – as you may have noticed from some screenshots – I used this implementation to check out VS2010 beta.

A quick verdict about VS 2010 beta (not really worth a separate post)…

The core system, i.e. the shell, the C# code editor, build system, etc. feels very good. No apparent bugs, quite fast, including intellisense, and close enough to VS2008 to feel familiar. Considering that big parts of this are complete rewrites, this is quite an achievement.

The visual designer for (Silverlight) XAML works nice for user controls. Designing grids, the property pane, and other tasks, is at first glance en par with Blend, but comes in a more familiar „Visual Studio flavor“; still it feels more rich and mature than VS2008.
However, there are some notable gaps. Editing of styles and templates, animations, and visual state manager are not covered. Thus my guess is that Blend will remain a necessary complement to VS, even if one has to switch less often. BTW: Contrary to what Tim wrote, I could work with Blend on VS2010 solutions (the project that cannot be loaded is only the web project), I just refrained from manipulating my project files with Blend.

Other areas I touched briefly have been less satisfying. IntelliTrace didn’t work, but I didn’t spend too much time on that. The architecture and modeling area for example has changed, but is by no means bug free (to the point of “not yet usable”). The profiler has evolved, but IMO still lacks what DevPartner offered nearly 10 years ago: a decent call graph.

Oh, one bright spot for any dev lead: code analysis (FxCop) rules are now maintained in separate files, projects reference these files by name.

Anyway, I have been using VS2010 beta since I installed it and was never compelled to switch back to VS2008. I’m going to have to reinstall my machine anytime soon, and I’m planning on going along with VS2010 beta, not installing VS2008 at all.

That’s all for now folks,
AJ.NET

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