Piotr Puszkiewicz's Silverlight Blog : Silverlight

Automatically Start Silverlight on Install - Part 2

PiotrP — Sat, 31 May 2008 04:11:00 GMT

Silverlight 2 changes the default instantiation model of the Silverlight control from Silverlight.js to the <object> tag. This change makes it seem that Automatically Starting Silverlight on Install requires rewriting our instantiation code and moving back to the Silverlight.js model. Fortunately, you can get the same auto-restart behavior using the <object> model.

My previous post on this subject called out that you need three things to build the auto-restart experience:

A method for asking the browser if Silverlight is installed repeatedly, but without locking up the site.
A way to tell that Silverlight is installed.
An action to take once Silverlight is available.

Only the second, a way to tell that Silverlight is installed, was provided by Silverlight.js. Everything else in that model is agnostic to the instantiation model. Since we can determine if Silverlight is installed using javascript without Silverlight.js we can rewrite the previous example to use the <object> instantiation method.

Background

These posts provide background information that will explain how/why this works:

Implementation

<html>

<head>

<title>Automatically Start Silverlight on Install</title>

WaitForInstallCompletion = function()

{

try

{

//This forces Firefox/Safari to refresh their

//list of known plugins.

navigator.plugins.refresh();

}

catch(e)

{

//IE does not support the method, so an

//exception will be thrown.

}

if ( isSilverlightInstalled() )

{

//Silverlight is installed. Refresh the page.

window.location.reload(false);

}

else

{

//Wait 3 seconds and try again

setTimeout(WaitForInstallCompletion, 3000);

}

};

onLoad = function()

{

//This only works if we are performing a clean install,

//not an upgrade.

if ( !isSilverlightInstalled() )

{

//Silverlight is not installed. Try to refresh

//the page when it is installed.

WaitForInstallCompletion();

}

function isSilverlightInstalled()

{

var isSilverlightInstalled = false;

try

{

//check on IE

try

{

var slControl = new ActiveXObject('AgControl.AgControl');

isSilverlightInstalled = true;

}

catch (e)

{

//either not installed or not IE. Check Firefox

if ( navigator.plugins["Silverlight Plug-In"] )

{

isSilverlightInstalled = true;

}

catch (e)

{

//we don't want to leak exceptions. However, you may want

//to add exception tracking code here.

}

return isSilverlightInstalled;

}

</script>

</head>

</a>

</object>

</div>

</body>

</html>

Explanation

As you can see, I replaced the call to Silverlight.isInstalled("1.0") with a call to isSilverlightInstalled(); Since we don't care about the version of Silverlight, this function is sufficient. Next, I replaced the call to CreateSilverlight() and thus Silveright.js with a Silverlight <object> element. And that's it. The rest of this example works just like the Silverlight.js implementation.

Automatically Start Silverlight on Install - Part 1

PiotrP — Fri, 02 May 2008 22:39:00 GMT

The last step of the Silverlight installer is to ask the user to restart or refresh their browser. This approach forces the browser to re-evaluate the page's Silverlight instantiation logic once the control is installed. In the case of non-IE browsers, the restart also forces the browser to refresh its cache of known controls.

While this experience is sufficient for most websites, it can be disruptive to sites which want to provide a managed end-to-end user experience. Fortunately, through the use of some simple javascript, these websites can detect when Silverlight installation completes and can launch their Silverlight content without any further user interaction.

Prerequisites

To get started, we need several logical components:

A method for asking the browser if Silverlight is installed repeatedly, but without locking up the site.
A way to tell that Silverlight is installed.
An action to take once Silverlight is available.

For the first component we can use the commonly available setTimeout and setInterval methods. For the purposes of this post I will use setTimeout since it doesn't require us to explicitly cancel future executions. You should evaluate both methods and determine which works best for your scenario.

The second component is also rather easy. The Silverlight.js helper file, available in the Silverlight SDK, provides a method named isInstalled which answers this very question.

Finally, what action should the page take when it detects that Silverlight is installed? The simplest answer is to refresh itself. This will enable the default instantiation logic to render the Silverlight application without any additional modifications.

Implementation

<html>

<head>

<title>Automatically Start Silverlight on Install</title>

WaitForInstallCompletion = function()

{

try

{

//This forces Firefox/Safari to refresh their

//list of known plugins.

navigator.plugins.refresh();

}

catch(e)

{

//IE does not support the method, so an

//exception will be thrown.

}

if ( Silverlight.isInstalled("1.0") )

{

//Silverlight is installed. Refresh the page.

window.location.reload(false);

}

else

{

//Wait 3 seconds and try again

setTimeout(WaitForInstallCompletion, 3000);

}

};

onLoad = function()

{

//This only works if we are performing a clean install,

//not an upgrade.

if ( !Silverlight.isInstalled("1.0") )

{

//Silverlight is not installed. Try to refresh

//the page when it is installed.

WaitForInstallCompletion();

}

</script>

</head>

<!—-

These references should be changed to point at the corresponding files in your web application

-->

createSilverlight();

</script>

</div>

</body>
</html>

Limitations
This approach is limited to new installations of Silverlight. Websites which require a newer version of Silverlight than what is already installed on the user's machine will still require a restart. Fortunately, Silverlight's automatic updater makes new version requirements a transient problem.

Conclusion
The Silverlight installation process provides a good user experience with minimal requirements for the web author. The script solution presented in this post builds on the default experience by helping websites take more control their end-to-end flow.