Question

I want to let application user know that whom buddy has downloaded the application which application is going to be used by him from his contact list. I mean is that possible that the application user can know from his contact lists that the other persons which are in his contact lists have downloaded the same application. is that possible?

same way as viber application.

Can we not figure out which one of their contacts has downloaded the app?

is there other way like this to implement.
What info can we get from their contact list?

What info can we get about the user? (city, email address, phone #, age, gender)

Answer 1

Yeah its possible, thats one of the advantages of using social networking as logins instead of providing ones own Facebook Connect. Once a user logs into your network using any one of these social networks potentially you can get a list of friends of the user so if any of his friend joins your service some days later matching the primary key would tell you that one of his friend used this service few days back etc.

1. User X logs in to your service using Facebook Connect.
2. Along with logging him to your service, you also collect this users friends ids.
3. Few days later some other user Y logs in to your service using same method as 1
4. After collecting his friends ids. You lookup in your DB which if User Y’s friend Ids you already have. put them in a set S. So S provides a list of all those users who are friends of Y and are already part of your service. Isn’t this the list you want?

Hope this is clear.