In the previous article, we’ve introduced contracts in Windows 8. To quickly recapitulate, a contract allows Metro style applications in Windows 8 to communicate which each other or with Windows, without there being a hard reference between the participants of the communication. We’ve seen how the search contract allows applications to open themselves up to Windows so they can be search. There’s of course a contract that specifies how this searching is to be done: an application has to follow the rules specified in the contract so that Windows can communicate with the app in the way it needs to do.
In this article, we’ll dive some more in contracts, more specifically, the share contract.
The code for this article can be downloaded here.
We love sharing
Sharing information has become something very trivial. Millions of sites out there have sharing options. “Share this on Twitter”, “Post on Facebook”, “Share via mail” and tons of other options have been popping up everywhere on the internet. Why? People love sharing. When they find something cool or they’ve just read the most interesting article, people want to share that with their contacts. Perhaps they want to broadcast it, using a social network. Or perhaps they want to target a specific contact and send the information via mail. Also, people sometimes want to share information related to something they have done or found inside an application. Perhaps they’ve achieved a high-score in some game and they want to brag with it. Or, they have found a great recipe in a cookbook application.
As you can see, sharing is all around us. One problem though is the fact that it’s sometimes still too hard for people to quickly share the information they want to share. As said, a lot of sites have embedded sharing icons. But are they always easy to find? Or what happens if you use a social network that the site you’re using isn’t listed? In that case you need to go and paste the link to the social networking site. Or as mentioned with the game high-scores: if the game doesn’t support sharing, how are you going to proof that you’ve really attained that high-score? Perhaps through a screenshot that you manually have to take, copy and paste to another site or application.
From a developer’s perspective as well, implementing the right sharing options can be hard. Sites offer often quite a few sharing options and maintaining all these external links can be a time-consuming task. What if tomorrow Twitter decides they want to implement that option differently? You as the developer need to go and change your implementation. And even then, perhaps the visitor of your site (or user from your application) uses some obscure social network (perhaps one that’s relevant in his home country) that you haven’t implemented…
Microsoft thought about offering an integrated sharing experience in Windows 8. It’s built into the system to offer both the end-user and the developer an easy and universal way of sharing information. This is the share contract.
The share contract
Through the share contract, Windows 8 makes it possible for 2 applications to share information with each other. The big plus for developers is that the 2 application don’t have to know each other. Sharing is always done between two applications: the share source and the share target. The share source will share information in a specific format defined by the contract; the share target will be getting that information through Windows. Since the information is in a specific format, the developer of the share target can anticipate on this and write his code based on this format.
Note that Windows is the mediator between the two apps. It handles the process of getting the information from the share source and getting it to the share target. It’s safe to say that we have some kind of pub/sub architecture.
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