UIKitLegacyDetector.m

BOOL PSPDFIsUIKitFlatMode(void) {
    static BOOL isUIKitFlatMode = NO;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        if (kCFCoreFoundationVersionNumber >= kCFCoreFoundationVersionNumber_iOS_7_0) {
            PSPDFAssertIfNotMainThread();

            // If your app is running in legacy mode, tintColor will be nil - else it must be set to some color.
            if (UIApplication.sharedApplication.keyWindow) {
                isUIKitFlatMode = [UIApplication.sharedApplication.keyWindow performSelector:@selector(tintColor)] != nil;
            }else {
                // Possible that we're called early on (e.g. when used in a Storyboard). Adapt and use a temporary window.
                isUIKitFlatMode = [[UIWindow new] performSelector:@selector(tintColor)] != nil;
            }
        }
    });
    return isUIKitFlatMode;
}