Code to detect whether this is an initial app launch or subsequent.

PreviouslyLaunched.mm

// Objective C++
// Detects whether this is an initial or subsequent launch of this app.
//
// By Andrew Kingdom
// MIT license
// 
static BOOL _appDidLaunchPreviously;
static BOOL _appDidLaunchPreviously_known;
static NSString * kAppDidLaunchPreviously = @"priorLaunch";
static NSString * vAppDidLaunchPreviously = @"Y";
/// Put this in the AppDelegate
/// Usage: BOOL initialLaunch = ! AppDelegate.appDidLaunchPreviously;
/// Returns FALSE if this is the app's first launch.
/// This changes the second time the app re-launches, not the second time this is called.
/// (Not thread safe as-is)
+ (BOOL)appDidLaunchPreviously {  // getter
    
    if(_appDidLaunchPreviously_known == TRUE) {
        // We already know the value, so return it
        return _appDidLaunchPreviously;
    }
    
    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
    // Get the value if defined
    id value = [defaults valueForKey:kAppDidLaunchPreviously];
    if(value == nil) {
        // If not defined, set the value (once per install) -- we'll read it on next launch
        [defaults setValue:vAppDidLaunchPreviously forKey:kAppDidLaunchPreviously];
    }
    
    _appDidLaunchPreviously_known = TRUE;
    _appDidLaunchPreviously = [value isEqualToString:vAppDidLaunchPreviously];
    return _appDidLaunchPreviously;  // First launch
}