Check if my IOS application is updated

You could save a value (e.g. the current app version number) to NSUserDefaults and check it every time the user starts the app.

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    // ...

    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];

    NSString *currentAppVersion = [[NSBundle mainBundle] objectForInfoDictionaryKey:@"CFBundleShortVersionString"];
    NSString *previousVersion = [defaults objectForKey:@"appVersion"];
    if (!previousVersion) {
        // first launch

        // ...

        [defaults setObject:currentAppVersion forKey:@"appVersion"];
        [defaults synchronize];
    } else if ([previousVersion isEqualToString:currentAppVersion]) {
        // same version
    } else {
        // other version

        // ...

        [defaults setObject:currentAppVersion forKey:@"appVersion"];
        [defaults synchronize];
    }



    return YES;
}

The swift-2 version looks like this:

let defaults = NSUserDefaults.standardUserDefaults()

let currentAppVersion = NSBundle.mainBundle().objectForInfoDictionaryKey("CFBundleShortVersionString") as! String
let previousVersion = defaults.stringForKey("appVersion")
if previousVersion == nil {
    // first launch
    defaults.setObject(currentAppVersion, forKey: "appVersion")
    defaults.synchronize()
} else if previousVersion == currentAppVersion {
    // same version
} else {
    // other version
    defaults.setObject(currentAppVersion, forKey: "appVersion")
    defaults.synchronize()
}

The swift-3 version looks like this:

let defaults = UserDefaults.standard

let currentAppVersion = Bundle.main.object(forInfoDictionaryKey: "CFBundleShortVersionString") as! String
let previousVersion = defaults.string(forKey: "appVersion")
if previousVersion == nil {
    // first launch
    defaults.set(currentAppVersion, forKey: "appVersion")
    defaults.synchronize()
} else if previousVersion == currentAppVersion {
    // same version
} else {
    // other version
    defaults.set(currentAppVersion, forKey: "appVersion")
    defaults.synchronize()
}

you can store a app version number in NSUserDefaults and check it every time your app is launched. If the number is not available, its a fresh installation. If it is changed , it is an upgrade.

swift version with an important improvement over the accepted answer:

• using infoDictionary instead of objectForInfoDictionaryKey guaranties that the result is independent from device language, otherwise you may end up in some rare cases believing that there is an upgrade when in reality it is just a device language change
• using a UserDefaults key identical to the main Bundle infoDictionary for clarity on what is exactly stored
• factoring setting currentVersion code
• Swift 3 syntax

Code:

    let standardUserDefaults = UserDefaults.standard
    let shortVersionKey = "CFBundleShortVersionString"
    let currentVersion = Bundle.main.infoDictionary![shortVersionKey] as! String
    let previousVersion = standardUserDefaults.object(forKey: shortVersionKey) as? String
    if previousVersion == currentVersion {
        // same version
    } else {
        // replace with `if let previousVersion = previousVersion {` if you need the exact value
        if previousVersion != nil {
            // new version
        } else {
            // first launch
        }
        standardUserDefaults.set(currentVersion, forKey: shortVersionKey)
        standardUserDefaults.synchronize()
    }

Swift 3.x

Just initialise AppVersionUpdateNotifier in app launch and conform AppUpdateNotifier protocol, enjoy.

class AppVersionUpdateNotifier {
    static let KEY_APP_VERSION = "key_app_version"
    static let shared = AppVersionUpdateNotifier()

    private let userDefault:UserDefaults
    private var delegate:AppUpdateNotifier?

    private init() {
        self.userDefault = UserDefaults.standard
    }

    func initNotifier(_ delegate:AppUpdateNotifier) {
        self.delegate = delegate
        checkVersionAndnotify()
    }

    private func checkVersionAndnotify() {
        let versionOfLastRun = userDefault.object(forKey: AppVersionUpdateNotifier.KEY_APP_VERSION) as? Int
        let currentVersion = Int(Bundle.main.buildVersion)!

        if versionOfLastRun == nil {
            // First start after installing the app

        } else if versionOfLastRun != currentVersion {
            // App was updated since last run
            delegate?.onVersionUpdate(newVersion: currentVersion, oldVersion: versionOfLastRun!)
        } else {
            // nothing changed

        }
        userDefault.set(currentVersion, forKey: AppVersionUpdateNotifier.KEY_APP_VERSION)
    }
}

protocol AppUpdateNotifier {
    func onFirstLaunch()
    func onVersionUpdate(newVersion:Int, oldVersion:Int)
}
extension Bundle {
    var shortVersion: String {
        return infoDictionary!["CFBundleShortVersionString"] as! String
    }
    var buildVersion: String {
        return infoDictionary!["CFBundleVersion"] as! String
    }
}
//*************************
//Use: Example
//*************************

extention AppDelagate: AppUpdateNotifier {
    func onVersionUpdate(newVersion: Int, oldVersion: Int) {
        // do something
    }

    func onFirstLaunch() {
        //do something
    }
}

Here is a simple code to know if the current version is different (this code work on simulator too.)

-(BOOL) needsUpdate
{
    NSDictionary* infoDictionary = [[NSBundle mainBundle] infoDictionary];
    NSString* appID = infoDictionary[@"CFBundleIdentifier"];
    NSURL* url = [NSURL URLWithString:[NSString stringWithFormat:@"http://itunes.apple.com/lookup?bundleId=%@", appID]];
    NSData* data = [NSData dataWithContentsOfURL:url];
    NSDictionary* lookup = [NSJSONSerialization JSONObjectWithData:data options:0 error:nil];

   if ([lookup[@"resultCount"] integerValue] == 1)
   {
       NSString* appStoreVersion = lookup[@"results"][0][@"version"];
       NSString* currentVersion = infoDictionary[@"CFBundleShortVersionString"];
       if (![appStoreVersion isEqualToString:currentVersion])
       {
           NSLog(@"Need to update [%@ != %@]", appStoreVersion, currentVersion);
           return YES;
       }
    }
    return NO;
}

Note: Make sure that when you enter the new version in iTunes, this matches the version in the app you are releasing. If not then the above code will always return YES regardless if the user updates.