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A windows 8 trick: Protocol activation of apps (and the nick app)

Pete Brown - 05 December 2012

I have a four year old girl and an almost seven year old boy. From time to time, my son will play games on the nick jr web site, or watch a video.

Nick has a portal-style app for Windows 8. This app provides access to videos and photos, as well as links out to games. Notice how even on my low DPI 30" screen, the tiles are large and everything is nicely scaled on the hub page. I've seen apps which have just a tiny bit of the screen filled, and that makes me sad -- this is a better implementation for almost zero extra effort.


That bit of green slime at the top? Besides being a classic Nickelodeon item, it's also something which invites you to click/touch. (Well, it does to a kid anyway.) What happens when you click it? It displays the navigation app bar. Pretty clever.


One of the Nickelodeon properties my kids both like is SpongeBob SquarePants. He has his own second level hub page as shown here.


Everything is appropriately branded, and kid-friendly (assuming you consider spongebob "kid-friendly". I know opinions differ there). This may at first seem like a typical "bunch of boxes" app, but it does it in a way which is appropriate to the properties and audience.

When you click on a video, it plays directly in the app, full screen.

image image

Winx club is another interesting property for Nickelodeon, and another that my kids both like. It's a bit like Disney Fairies meet Bratz or Monster High or something else I've seen in that aisle at the store during Christmas shopping.


As with SpongeBob, the video player is inline. The overlays are there only for a second or two and only if you move the mouse or touch the screen. The fairy with the red hair is actually pleased to get that gift, but I think she's too cool to show it ;)


So, overall, a typical media portal experience target to kids. It's simple and well-done.

Games and the browser

What's really interesting to me is what happens when you launch a game. Nickelodeon didn't port their games to Windows 8, but instead decided to leverage their existing games and launch them in the browser, directly from the app. The upside to this is the obvious savings in effort. The downside is that the game is really tiny on my giant screen. In their defense, it's rare to find a child with a 30" screen running at 256ox1600 :). On a smaller screen, it looks just fine, but I'd like to see them do a little scaling in a future update.

When the nick app launches the game, this is an example of the URL they use:


See that little "Close game" button on the top right? That (after a prompt) closes the browser and returns you to the page you were on in the nick app. How does it do that?

Protocol activation of apps

Nickelodeon is using protocol activation, as you can see from the markup in this listing.


Specifically, this is the URI format that they're using:

<div id="metro-game-header"
url="nickmetroapp://www.nick.com/callback?page=StarDetailPageViewModel&amp;param=hs_winx_club"><div class="header-container"><img width="569" height="128" id="header-logo" alt="Nickelodeon" src="http://images3.nick.com/nick-assets/games/nick-metro-app/nick-logo.png?height=128&amp;width=569&amp;quality=0.75"><img width="93" height="128" id="header-slime" src="http://images2.nick.com/nick-assets/games/nick-metro-app/slime-drop.png?height=128&amp;width=93&amp;quality=0.75"><img width="300" height="81" id="header-button" onclick="NICK.games.metro.appCallTriggered();" alt="Close Game" src="http://images2.nick.com/nick-assets/games/nick-metro-app/close-back-button.png?height=81&amp;width=300&amp;quality=0.75">

The parameter information comes from the URL that the app originally sent over.

If you have the nick app installed, click this link in your browser: nickmetroapp://www.nick.com/callback?page=StarDetailPageViewModel&param=hs_winx_club . It will pull up the nick app, just as you expect. Because of the parameter passed, it will even navigate to the specific page.

This works because apps can register protocols that they respond to. The primary reason this exists is to support things like browsers which respond to http and voip apps which need to respond to their own call-to protocols, but you can use it in your own apps.

Protocols are registered in the appxmanifest for the project. In this screen grab, I'm registering the pete-brown:// protocol. (For obvious reasons, there are a number of reserved protocols which you cannot register for your app. You can find them listed in this MSDN article.)


Once I deploy this app, if anyone enters "pete-brown://something_or_other" it will launch or activate my app. More on that in a moment.

What about multiple apps registering the protocol?

In Windows 8, the user is always in control. It's up to the user to decide which apps they will use to open specific file types or protocols. Via the prompts that come up when you open a file or URI (The "you have new apps which can open this type of file" prompt) and via the default programs in Control Panel, the user can decide which apps will be associated with the type.

Most users won't need to use this control panel section, but it's good to know it's there.



It's one thing to allow your app to be activated with just any random URI with your app's scheme/prefix, but what about passing parameters and whatnot?

Intelligently handling activation

Your app is in control of the URI format. You'll want to stick within the rules for URI formatting in general, but how you interpret what you see is up to you.

Inside App.xaml, override the OnActivated method and handle the case of protocol activation as shown here:

protected override void OnActivated(IActivatedEventArgs args)
if (args.Kind == ActivationKind.Protocol)
var protocolArgs = args as ProtocolActivatedEventArgs;

var fullUri = protocolArgs.Uri;

// todo: parse the URI and navigate to the appropriate
// page, or perform an action


Once you have the Uri, you can break it into its component pieces.


When you handle this type of activation, your app may already be running, or it may be a brand new activation and launch. Be sure to handle each case appropriately.

What could you use it for?

It's increasingly common for apps to provide deep links to their data. Contacts stores need to provide ways to link to specific contacts, for example.

This is especially important when it comes to implementing the Share contract. In that case, when you share something like a contact, you may want to simply provide a deep link to that contact's information in your app. This will allow you to share the link with anyone who already has that app. Same concept applies to customer information, or invoices, or other potentially useful app information.

One thing that makes Windows Store apps powerful is that they all play together to make the sum greater than the parts. The Share contract is a huge part of that, but so is protocol activation. Consider implementing it in your next Windows Store app.

posted by Pete Brown on Wednesday, December 5, 2012
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