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Guest Post: Using IronRuby and .NET to produce the ‘Hello World of WPF’

- by Eric Nelson

[You might want to also read other GuestPosts on my blog – or contribute one?] On the 26th and 27th of March (2010) myself and Edd Morgan of Microsoft will be popping along to the Scottish Ruby Conference. I dabble with Ruby and I am a huge fan whilst Edd is a “proper Ruby developer”. Hence I asked Edd if he was interested in creating a guest post or two for my blog on IronRuby. This is the second of those posts. If you should stumble across this post and happen to be attending the Scottish Ruby Conference, then please do keep a look out for myself and Edd. We would both love to chat about all things Ruby and IronRuby. And… we should have (if Amazon is kind) a few books on IronRuby with us at the conference which will need to find a good home. This is me and Edd and … the book: Order on Amazon: http://bit.ly/ironrubyunleashed Using IronRuby and .NET to produce the ‘Hello World of WPF’ In my previous post I introduced, to a minor extent, IronRuby. I expanded a little on the basics of by getting a Rails app up-and-running on this .NET implementation of the Ruby language — but there wasn't much to it! So now I would like to go from simply running a pre-existing project under IronRuby to developing a whole new application demonstrating the seamless interoperability between IronRuby and .NET. In particular, we'll be using WPF (Windows Presentation Foundation) — the component of the .NET Framework stack used to create rich media and graphical interfaces. Foundations of WPF To reiterate, WPF is the engine in the .NET Framework responsible for rendering rich user interfaces and other media. It's not the only collection of libraries in the framework with the power to do this — Windows Forms does the trick, too — but it is the most powerful and flexible. Put simply, WPF really excels when you need to employ eye candy. It's all about creating impact. Whether you're presenting a document, video, a data entry form, some kind of data visualisation (which I am most hopeful for, especially in terms of IronRuby - more on that later) or chaining all of the above with some flashy animations, you're likely to find that WPF gives you the most power when developing any of these for a Windows target. Let's demonstrate this with an example. I give you what I like to consider the 'hello, world' of WPF applications: the analogue clock. Today, over my lunch break, I created a WPF-based analogue clock using IronRuby... Any normal person would have just looked at their watch. - Twitter The Sample Application: Click here to see this sample in full on GitHub. Using Windows Presentation Foundation from IronRuby to create a Clock class Invoking the Clock class Gives you The above is by no means perfect (it was a lunch break), but I think it does the job of illustrating IronRuby's interoperability with WPF using a familiar data visualisation. I'm sure you'll want to dissect the code yourself, but allow me to step through the important bits. (By the way, feel free to run this through ir first to see what actually happens). Now we're using IronRuby - unlike my previous post where we took pure Ruby code and ran it through ir, the IronRuby interpreter, to demonstrate compatibility. The main thing of note is the very distinct parallels between .NET namespaces and Ruby modules, .NET classes and Ruby classes. I guess there's not much to say about it other than at this point, you may as well be working with a purely Ruby graphics-drawing library. You're instantiating .NET objects, but you're doing it with the standard Ruby .new method you know from Ruby as Object#new — although, the root object of all your IronRuby objects isn't actually Object, it's System.Object. You're calling methods on these objects (and classes, for example in the call to System.Windows.Controls.Canvas.SetZIndex()) using the underscored, lowercase convention established for the Ruby language. The integration is so seamless. The fact that you're using a dynamic language on top of .NET's CLR is completely abstracted from you, allowing you to just build your software. A Brief Note on Events Events are a big part of developing client applications in .NET as well as under every other environment I can think of. In case you aren't aware, event-driven programming is essentially the practice of telling your code to call a particular method, or other chunk of code (a delegate) when something happens at an unpredictable time. You can never predict when a user is going to click a button, move their mouse or perform any other kind of input, so the advent of the GUI is what necessitated event-driven programming. This is where one of my favourite aspects of the Ruby language, blocks, can really help us. In traditional C#, for instance, you may subscribe to an event (assign a block of code to execute when an event occurs) in one of two ways: by passing a reference to a named method, or by providing an anonymous code block. You'd be right for seeing the parallel here with Ruby's concept of blocks, Procs and lambdas. As demonstrated at the very end of this rather basic script, we are using .NET's System.Timers.Timer to (attempt to) update the clock every second (I know it's probably not the best way of doing this, but for example's sake). Note: Diverting a little from what I said above, the ticking of a clock is very predictable, yet we still use the event our Timer throws to do this updating as one of many ways to perform that task outside of the main thread. You'll see that all that's needed to assign a block of code to be triggered on an event is to provide that block to the method of the name of the event as it is known to the CLR. This drawback to this is that it only allows the delegation of one code block to each event. You may use the add method to subscribe multiple handlers to that event - pushing that to the end of a queue. Like so: def tick puts "tick tock" end timer.elapsed.add method(:tick) timer.elapsed.add proc { puts "tick tock" } tick_handler = lambda { puts "tick tock" } timer.elapsed.add(tick_handler) The ability to just provide a block of code as an event handler helps IronRuby towards that very important term I keep throwing around; low ceremony. Anonymous methods are, of course, available in other more conventional .NET languages such as C# and VB but, as usual, feel ever so much more elegant and natural in IronRuby. Note: Whether it's a named method or an anonymous chunk o' code, the block you delegate to the handling of an event can take arguments - commonly, a sender object and some args. Another Brief Note on Verbosity Personally, I don't mind verbose chaining of references in my code as long as it doesn't interfere with performance - as evidenced in the example above. While I love clean code, there's a certain feeling of safety that comes with the terse explicitness of long-winded addressing and the describing of objects as opposed to ambiguity (not unlike this sentence). However, when working with IronRuby, even I grow tired of typing System::Whatever::Something. Some people enjoy simply assuming namespaces and forgetting about them, regardless of the language they're using. Don't worry, IronRuby has you covered. It is completely possible to, with a call to include, bring the contents of a .NET-converted module into context of your IronRuby code - just as you would if you wanted to bring in an 'organic' Ruby module. To refactor the style of the above example, I could place the following at the top of my Clock class: class Clock include System::Windows::Shape include System::Windows::Media include System::Windows::Threading # and so on... And by doing so, reduce calls to System::Windows::Shapes::Ellipse.new to simply Ellipse.new or references to System::Windows::Threading::DispatcherPriority.Render to a friendlier DispatcherPriority.Render. Conclusion I hope by now you can understand better how IronRuby interoperates with .NET and how you can harness the power of the .NET framework with the dynamic nature and elegant idioms of the Ruby language. The manner and parlance of Ruby that makes it a joy to work with sets of data is, of course, present in IronRuby — couple that with WPF's capability to produce great graphics quickly and easily, and I hope you can visualise the possibilities of data visualisation using these two things. Using IronRuby and WPF together to create visual representations of data and infographics is very exciting to me. Although today, with this project, we're only presenting one simple piece of information - the time - the potential is much grander. My day-to-day job is centred around software development and UI design, specifically in the realm of healthcare, and if you were to pay a visit to our office you would behold, directly above my desk, a large plasma TV with a constantly rotating, animated slideshow of charts and infographics to help members of our team do their jobs. It's an app powered by WPF which never fails to spark some conversation with visitors whose gaze has been hooked. If only it was written in IronRuby, the pleasantly low ceremony and reduced pre-processing time for my brain would have helped greatly. Edd Morgan blog Related Links: Getting PhP and Ruby working on Windows Azure and SQL Azure

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