How to know if user has updated app or installed a fresh copy?

Question

I will be sending out an update to my app with a new data structure, therefore if a user is updating my app I need to update their current data. So I was wondering how can I programatically tell if the user updated my app or installed a new copy (if a new copy is installed I don't need to update anything) ?

Answer 1

Checking the data structure is a solid solution. I began to worry in my own apps about folks who don't upgrade for several versions. I felt this would lead to a myriad of structure checks. The code I show below determines and stores the version and previous version in the NSUserDefaults. You could code for those varying version difference scenarios if needed.

NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults];
BOOL versionUpgraded;
NSString *version = [[[NSBundle mainBundle] infoDictionary] objectForKey:@"CFBundleVersion"];
NSString *preVersion = [prefs stringForKey:@"appVersion"];

if ([prefs stringForKey:@"appVersion"] != nil) {
    //see if version is the same as prior
    //if not it is an Upgraded
    versionUpgraded = !([preVersion isEqualToString: version]);
} else {
    //nil means new install
            //This needs to be YES for the case that
            //"appVersion" is not set anywhere else.
    versionUpgraded = YES; 
}

if (versionUpgraded) {
    [prefs setObject:version forKey:@"appVersion"];
    [prefs setObject:preVersion forKey:@"prevAppVersion"];

    [prefs synchronize];
}

Answer 2

That depends on the kind of data structure you're using.

In general, I would advise you against relying on checking your application version: a user using 2.0 might have just upgraded or it might be a new user.

I'd rather check if there's a data structure already, and act accordingly. Assuming that you're using a Sqlite-backed Core Data storage, you can either check whether the .sqlite file exists, or check if there are objects in your storage.