Question

Let’s say I have app on iPhone and Windows Phone 7. How to share (ex. Note) between my both apps, regardless any platform.

Update

Guess this question is very broad, my bad.

Be more specific, I want the user to go through his contact list and share through my app. How do I identify if the other user installed my app? and what platform he/she using?

Answer 1

Using the contact list isn’t a good way to “share” in this regard.

You’re asking two questions here:

1. How to build a system to share data between two mobile clients, irrespective of platform?
2. How to best enable users to find their friends to share data?

Let’s start with the 2nd question.

I would leverage services like Twitter and Facebook and have your app connect with your users facebook account. This is a well known approach, and avoids having to roll your own account system.

With facebook as an example:
Facebook connect, you can get the facebookID of your user, as well as their friends facebookID. You’ll need a backend webservice which you can query users by fbID.

When a user opts to use their facebook account, store their FacebookID on your backend service. Then using facebook’s api’s get a list of their friends facebookID’s. Your app will lookup each ID using your backend service, and if it finds one, then you know that friend has also installed the app, and connected it to facebook.

So if Alice installed your app, connects to facebook, and she is friends with Bob, who also has installed your app, your back end service would return that Bob’s facebookID is known to your app, and thus the two of them can share to each other using some protocol that you design.

If their friend’s ID isn’t known to your system, I would send them a facebook message, or post on thier wall with a restful link that invites them to check out the note you want to share on the web, and place the link to the app on the same page.

Due to the high level of your question, this answer is a bit of a 20,000ft view, and assumes you know how to build a web service.

If you want to see a great example of an app that makes use Facebook and or Twitter to find friends who also use the same app, I recommend checking out Groupme. It’s free, and available for WP7, iPhone, and Android. It’s a group SMS app, and uses your contact list, facebook, and twitter, to setup friends.

For the first question, you’ll need to make use of a backend webservice. User would elect to share either in-app, or by posting to their facebook, with a weblink. In-app sharing, I would use an inbox approach. A user posts a message to their friend, and it gets stored in a queue. The app periodically checks the users queue to see if any new “shares” have been posted. If so, get that data, and present it to the user. Your back end service should also take advantage of newer app concepts like push notifications, because thats what users expect.