Know when the App is launched for the first time in IOS

In objective C:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    if (![[NSUserDefaults standardUserDefaults] boolForKey:@"HasLaunchedOnce"])
    {
        [[NSUserDefaults standardUserDefaults] setBool:YES forKey:@"HasLaunchedOnce"];
        [[NSUserDefaults standardUserDefaults] synchronize];
    }
    return YES;
}

In swift using NSUserDefault:

 let launchedBefore = NSUserDefaults.standardUserDefaults().boolForKey("launchedBefore")
if launchedBefore  {
    print("anteriormente iniciada.")
}
else {
    print("Se inicia por primera vez!..")
    NSUserDefaults.standardUserDefaults().setBool(true, forKey: "launchedBefore")
}

Completing the answer, you first fill in the variable

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
    {
        if (![[NSUserDefaults standardUserDefaults] introducir el código aquíboolForKey:@"HasLaunchedOnce"])
        {
            [[NSUserDefaults standardUserDefaults] setBool:YES forKey:@"HasLaunchedOnce"];
            [[NSUserDefaults standardUserDefaults] synchronize];
        }
        return YES;
    }

Then read the variable if you need it somewhere

 NSString *value = [[NSUserDefaults standardUserDefaults] stringForKey:@"HasLaunchedOnce"];

I add the code for Swift 4

Save data:

UserDefaults.standard.set(<value>, forKey: "key_name")
UserDefaults.standard.synchronize() //Optional

Retrieve data

var returnValue: [datatype]? = UserDefaults.standard.object(forKey: "key_name") as? [datatype]

And I also add delete them , which in the previous answers is not:

UserDefaults.standard.removeObject(forKey:"key_name")