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by Mathias 12/2/2007 4:56:00 PM

Unless you are living (and working) under a rock, if you are a .NET developer, you must have come across the word Silverlight in the past few months. In a nutshell, “Microsoft® Silverlight™ is a cross-browser, cross-platform plug-in for delivering the next generation of .NET based media experiences and rich interactive applications for the Web”.

I have attended a few presentations about Silverlight recently, and was really impressed by the results. The thing is, demos ARE designed to look good – what they are not designed for is to show you the limitations of the technology. You will find that part on your own, when you start actually using it. I was pretty impressed by what Silverlight could do - I thought it was time for me to check out what Silvelight would actually do for me, on a real example. You can see the final result here.

Use case

Silverlight's announced strength is "fast, cost-effective delivery of high-quality video to all major browsers running on the Mac OS or Windows"; on the other hand, in its current released version (1.0), it comes with virtually no standard controls out of the box. Therefore, I chose a project light on controls, but where video playing was crucial, and decided to refactor a page of my personal website, where visitors can choose from a list of videos, and play them on the page. I was never satisfied with the original page; the rendering was unpredictable, depending on the installation of the media player plugin in the browser.

The use case for the page is:

The user is presented the choice between multiple videos
The user selects a video
The system accesses the video through its url
The system plays the video

Solution

The solution implemented is very simple - you can watch the result here. I created a main Silverlight control, defined through a xaml file, containing 5 “buttons”, each of them corresponding to the selection of a video, and a “video player” to play them. I also created a plain html page, with a a div section to host the Silverlight control. The control is instantiated through a javascript in its own file:

[code:html]

<script type="text/javascript">

function createMySilverlightPlugin()
{
   Silverlight.createObject(

   "VideoPlayer.xaml",

   parentElement,

   "videoControlHost",

   { width:'800', height:'500', inplaceInstallPrompt:false, background:'white', isWindowless:'false', framerate:'24', version:'1.0'},

   { onError:null, onLoad:null },

   null);

}

</script>

[/code]

The control is organized through a xaml file, which contains a main canvas (the outermost container for the control) and 6 canvasses for each of the controls. Each nested canvas contains information defining its location in the main canvas, and the type, appearance and behavior of each control, through xml-style tags and attributes. (For brevity, I omitted the canvasses for button 3 to 6).

[code:xml]

<Canvas
   xmlns="http://schemas.microsoft.com/client/2007"
   xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
   Height="400" Width="400" Background="white" Canvas.Left="100" Canvas.Top="100">

<Canvas
      MouseLeftButtonDown="PlayTrack1"
      MouseEnter="EnterTrack1Button"
      MouseLeave="LeaveTrack1Button"
      Canvas.Left="5" Canvas.Top="5">
    <Rectangle x:Name="playTrack1Rectangle"
      Stroke="#d0d0d0" StrokeThickness="2" Fill="white"
       Height="30" Width="150" RadiusX="3" RadiusY="3" >
    </Rectangle>
    <TextBlock
      Canvas.Left="5" Canvas.Top="5" Text="Mission and 18th" FontFamily="Verdana" Foreground="black" />
</Canvas>

<Canvas
      MouseLeftButtonDown="PlayTrack2"
      MouseEnter="EnterTrack2Button"
      MouseLeave="LeaveTrack2Button"
      Canvas.Left="5" Canvas.Top="45">
    <Rectangle x:Name="playTrack2Rectangle"
      Stroke="#d0d0d0" StrokeThickness="2" Fill="white"
       Height="30" Width="150" RadiusX="3" RadiusY="3">
    </Rectangle>
    <TextBlock
      Canvas.Left="5" Canvas.Top="5" Text="Door" FontFamily="Verdana" Foreground="black" />
</Canvas>

<Canvas
    Canvas.Left="170" Canvas.Top="5">
    <Rectangle x:Name="borderAroundVideo"
       Stroke="#d0d0d0" StrokeThickness="2" Fill="white"
       Width="420" Height="320"
       RadiusX="3" RadiusY="3">
    </Rectangle>
    <MediaElement x:Name="VideoDisplay"
      Source="door.wmv"
      Width="400" Height="300"
      Canvas.Top="10" Canvas.Left="10"/>
</Canvas>

</Canvas>

[/code]

Each button has a MouseLeftButtonDown event, defined in the xaml file. Its property is set to a string which corresponds to the name of a javascript function hosted on the html page. The event triggers a javascript specific to the selected button, which stops whatever could be playing in the video player, sets the reference to the url of the video file specific to that button, and starts the video player.

In addition to that, each button has 2 events, MouseEnter and MouseLeave, which dynamically change the color of the box, through its property, when the mouse hovers over into and out of the box.

[code:html]

<script type="text/javascript">
    function PlayTrack1(sender, args)
    {
        sender.findName("VideoDisplay").stop();
        sender.findName("VideoDisplay").Source="http://www.brandewinder.com/movies/missionand18.wmv";
        sender.findName("VideoDisplay").play();
    }

    function EnterTrack1Button(sender, args)
    {
        sender.findName("playTrack1Rectangle").Fill="red";
    }
    function LeaveTrack1Button(sender, args)
    {
        sender.findName("playTrack1Rectangle").Fill="white";
    }

</script>

[/code]

Conclusion

I am reasonably familiar with web applications, but this is not my area of expertise; in particular, I have no expertise in Javascript – this was essentially my first time writing some javascript. Yet, I was surprised at how easy it was to get the video player to work. It took me about 2 hours, included reading through the tutorials (which are great, by the way), to get the page to the state you can see. Getting rich media to play with active x controls always looked to me like a form of dark magic, and IE and Firefox seem to always be fighting each other when it’s time to play audio or videos. Silverlight got this to work flawlessly in both browsers, in under 2 hours.

The code itself is very inelegant, and its limits are obvious to me. The amount of code duplication between the scripts corresponding to each of the buttons is ugly. This should blamed on my lack of knowledge of javascript, but it is also a choice; I wanted to get something to work quickly, and chose to display the code as is was after 2 hours of work, rather than show a full-fledge, polished solution. I will build on it soon to clean up these issues.

Silverlight lets you do amazing things with animations, so I had originally intended to have cool-looking buttons, animated when hovered on and clicked. That part turned out to be a bit more complex than I anticipated; I got it to nearly work, except that when the mouse was moved over the text label, it ceased to recognize that it was over the box. I think it is because the text label is over the box, and hides it, and I will try to get that resolved in my next iteration. However, the fact remains that using Visual Studio 2005 only, getting a simple button-like control took some work.

Finally, I had initially planned on hosting the xaml component in an ASP.NET page, and ran into problems. I could not figure out yet what the issue was; it seems to be related to using masterpages, themes, and possibly the fact that the masterpage contains a javascript. Silverlight does work with ASP.NET and masterpages, so this in itself is not the problem, but until I understand what is going on I had to opt temporarily for a simple html page.