gistfile1.m

- (void)flipButtonPressed:(id)sender
{
    if (self.currentView == self.primaryView) {
        self.cardBackView.showTellMeWhenSwitch = YES;
        __block UIImage *image = self.eventCardView.eventImageView.image;
        __weak GSEventStarCollectionViewCell *weakSelf = self;
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
            image = [image applyMediumDarkEffectWithBlurRadius:10.0f];
            dispatch_async(dispatch_get_main_queue(), ^{
                weakSelf.cardBackView.imageView.image = image;
            });
        });
    }    
    [self flipView];
}