Apps Checking Your Contacts

Hi,

I see more and more apps get you to use your mobile number for signup.

For example, when you sign up to Whatsapp, all it asks for is your mobile number, which is your unique ID.

When you open the app for the first time, Whatsapp accesses all of the contacts in your phonebook and checks which of those contacts are already using Whatsapp, by comparing your contact's numbers with the accounts on the Whatsapp server. If they find one of your contacts who is also on Whatsapp, they place your contact in your Whatsapp Favourites (Whatsapp contacts)

QUESTIONS
01 - how often would an app like this need to check / sync your contacts with their accounts database?

02 - has anyone ever come across a good article on signing up with mobile, from a developer point of view?

Thanks in advance for your help.

First WhatsApp would use your phone number to send the Text msg, so its understandable it would need that, and what better way to make your unique ID (personally, I think that would be better than giving out a email address for them to spam when ever they felt like.)

Secondly, it shouldn't have scanned any of your address book unless you gave it the authority to do so. When you first opened it, it would of asked for WhatsApp to access your contacts, just like FB and Twitter ask.
You could of said 'decline' and if you go into Settings>Privacy>Contacts you can turn off WhatsApp to having access to your Contacts.

As to how often it scans it, I would say when ever there is another contact added, it would know and see if its linked to WhatsApp servers. . .

Thanks for the reply.

I have no problem with it accessing my contacts as i think they use a very good method.

I'd like to resemble the same setup in an app that i am building so i would like to know more about this area.

Ahh ok, well your best bet is to hit the Apple Developer Forums and ask in there for help. There is a wealth of knowledge in there. But remember, if you copy a App or something that is unique to them, you could have trouble getting it past the review process. (not saying you will but just something to think about)

But if you ask in the forums over there, a way to achieve what you want, they can be quite helpful, in pointing you in the right direction.
And remember there is now Swift Programming Language too, so you don't have to do it all in Obj-C

Ok great, thanks.