How to avoid a blocked user interface during UIView animations with blocks

When you use the new iOS 4 UIView animations with blocks you will notice that the animations will lock user interaction while they are running. With really short animations this might be uncritical but it is surely unacceptable when a user cannot scroll a UIScrollView because another UIView is being animated with a longer duration like 2 seconds.

The reason for this “frozen UI problem” lies in the default value for the options mask of UIView’s animateWithDuration: methods. Apparently the option UIViewAnimationOptionAllowUserInteraction is not part of the default options mask. Unfortunately only one of the three animateWithDuration: methods allows to set the animation options. So to avoid the freezing of the user interface use animateWithDuration:delay:options:animations:completion: like in this example where a view is faded out over the duration of two seconds without blocking the user interface:

[UIView animateWithDuration:2.0 
        delay:0.0 
        options:UIViewAnimationOptionAllowUserInteraction 
        animations:^(void){yourview.alpha = 0.0} 
        completion:^(BOOL completed){yourview.hidden = YES;}];