Objective C:: How to check if the user already installed your app?

Question

I am new to iOS (iphone and ipad) development.

I am developing an app. In the app, at 1 point, I will need to retrieve the contact lists, and my question is, after I get the user's contact list, is it possible to check each user have/have not installed my app? If yes, how? If no, how does Viber works?

Answer 1

They have a database with phone numbers. And I guess they send all the phonenumbers in your contacts to a server and return those who use viber. But I'm just guessing, never installed their app.

From their FAQ:

You don't have to register! You know your phone number, and so do your friends, so why bother with yet another username and password? Viber uses your phone number as your "identity" and lets you make free Viber phone calls to any of your friends that have Viber - using THEIR phone number.

Answer 2

From strictly the point of view of checking if another application is already installed,I made use of UIPasteBoard once.We developed a standard of pasting some info based on a key and the app would check first if that particular app name is present it would not show that in offers