Tutor.com Classroom How-To #10: manually detecting and installing the Silverlight plug-in

These How-To tips are taken from The Tutor.com Classroom: Architecture and techniques using Silverlight, WPF, and the Microsoft .NET Framework.

You can check out the Silverlight Tutor.com Classroom in "practice" mode, although the real experience is with a live tutor on the other side!

Use the isInstalled() function provided by Silverlight.js:

<script language="javascript" type="text/javascript">

Silverlight.InstallAndCreateSilverlight = function(version)
{
  var retryTimeout = 1000; //the interval at which instantiation is attempted(ms)
  if (Silverlight.isInstalled(version))
  {
    ...
  }
  else if (!Silverlight.isInstalled(version))
  {
    TimeoutDelegate = function()
    {
      Silverlight.InstallAndCreateSilverlight(version);
    }

    setTimeout(TimeoutDelegate, retryTimeout);
  }
}

Silverlight.InstallAndCreateSilverlight('2.0.30923.0');

</script> 

beware of flash

sorry for the rant, but a couple of things came up today that wasted hours of time for me and are worth filing away in your flash development mental compartment.

adobe releases new flash builds frequently:

• there were 4 releases of flash 8 between august 2005 and september 2006 (plus 2 more “security enhancement” releases since then). release notes are here: http://www.adobe.com/support/documentation/en/flashplayer/8/releasenotes.html
• there have been 8 releases of flash 9 from august 2006 to december 2007. on the 3 computers i use frequently, i have 3 different versions of flash 9! release notes are here: http://www.adobe.com/support/documentation/en/flashplayer/9/releasenotes.html

you can see what version of flash you have installed here: http://kb.adobe.com/selfservice/viewContent.do?externalId=tn_15507

so what, you say? well, i mention this because i encountered a nasty bug with specific versions of flash 9 and ExternalCallback today. ExternalCallback is the interface that makes it easy to call from javascript into a flash movie. the bug is this: in IE, when a flash movie is inside a <form> tag, a cached flash movie is not properly re-loaded when it is pulled from the cache, and ExternalCallback just stops working. the bug was present or introduced at some point up to 9.0.44.0, but fixed by 9.0.115.0 (so i didn’t see it at first).

the fix (hack, really), is to append a unique querystring value to the .swf filename, so that IE never pulls the movie from the cache. this was acceptable in my case (an 8kb flash movie), but obviously wouldn’t have worked if the movie was larger.

another bug that was present in earlier versions of flash 9 caused IE to crash when a flash object was unloaded as the browser quit. the fix for that is just as nasty; get a load of this:

function cleanUpCounterObjects()
{
  var objects = document.getElementsByTagName("object");

  for (var i=0; i < objects.length; i++)
  {
    for (var x in objects[i])
    {
      if (typeof objects[i][x] == 'function')
        objects[i][x] = null;
    }
  }
}

beforeUnloadCounterObjects = function()
{
  //fix for memory bug with flash 9 and IE
  __flash_unloadHandler = function(){};
  __flash_savedUnloadHandler = function(){};

  window.attachEvent( "onunload", cleanUpCounterObjects );
}

if (window.attachEvent)
  window.attachEvent( "onbeforeunload", beforeUnloadCounterObjects);

i get it that cross-browser, cross-platform is hard to do, but doing flash development right is almost impossible with adobe’s versioning strategy. seems to me that side-by-side installations would solve all of these problems; developers could say “flash 9.0.45.0 only”, and when users update to 9.0.115.0, they actually just install it side-by-side with 9.0.45.0, so apps released for 9.0.45.0 continue to run in 9.0.45.0! or am i missing something?

again, just make sure you do as much testing as possible in different configurations. you can download older flash versions from adobe here:

http://kb.adobe.com/selfservice/viewContent.do?externalId=tn_14266&sliceId=1

and the flash uninstaller is here:

http://kb.adobe.com/selfservice/viewContent.do?externalId=tn_14157

good luck…

remember IE6

kind of goes along with the 1024x768 note: IE6 still accounts for 40% of our IE visits, and IE as a whole accounts for 80% of site visits. this means about 1 in 3 of all site visitors see what we do using IE6. this # is declining, but it’s still very much in play for now, so remember to check your work in IE6 in addition to IE7/Firefox. unfortunately, there are subtle differences in the IE rendering engines, and some things that work fine in IE7 just don’t in IE6.

when Firefox 3 comes out (fairly soon), we’ll have yet another browser to add to the make-sure-you-test-on list; ahhh, web development J

when doing GUI work, run your second monitor at 1024x768

remember that most of the world sees things very differently than we do, so make sure you frequently check your GUI work on a 1024x768 display; it’s still half of users. recent stats from our site:

1	1024x768	47.56%
2	1280x800	16.57%
3	1280x1024	10.05%
4	800x600	8.81%
5	1440x900	5.05%

click to run an ActiveX control

here’s the lowdown from Microsoft on the ‘click to run an ActiveX control’ dialog (affects plugins like flash, shockwave, and quicktime) and a fix for it (you need to create the object with javascript and not use an object tag):

http://msdn.microsoft.com/library/default.asp?url=/workshop/author/dhtml/overview/activating_activex.asp

more info:

http://www.cssbeauty.com/skillshare/comments.php?DiscussionID=482