Programming iOS 6, 3rd Edition

Address Book Database

The address book is an ABAddressBookRef obtained by calling ABAddressBookCreateWithOptions. This method is new in iOS 6. There are in fact no options to pass, so the first parameter is always nil. The important thing is the second parameter, a pointer to a CFErrorRef; if the result is nil, the CFErrorRef describes the error. The reason there can be an error is that the user can now deny your app access to the address book:

CFErrorRef err = nil;
ABAddressBookRef adbk = ABAddressBookCreateWithOptions(nil, &err);
if (nil == adbk) {
    NSLog(@"error: %@", err);
    return;
}

The very first time your app tries to access the address book, a system alert will appear, prompting the user to grant your app permission to access the user’s Contacts. You can modify the body of this alert by setting the “Privacy — Contacts Usage Description” key (NSContactsUsageDescription) in your app’s Info.plist to tell the user why you want to access the address book. This is a kind of “elevator pitch”; you need to persuade the user in very few words.

You can learn beforehand whether access has been explicitly denied by calling ABAddressBookGetAuthorizationStatus:

ABAuthorizationStatus stat = ABAddressBookGetAuthorizationStatus();
if (stat==kABAuthorizationStatusDenied ||
    stat==kABAuthorizationStatusRestricted) {
    NSLog(@"%@", @"no access");
    return;
}

If the user has denied your app access, you can’t make the system alert appear again. You can, of course, use some other interface to request that ...