Objective-C – Queuing up and delaying UIKit messages - objective-c

Question

I'm delaying UIKit messages as per this SO answer
Now another requirement has arisen, instead of just queuing SSHUDView method calls we should also handle queing of UIAlertView. For example one scenario could be that we display a hud then after 1 second we display another hud and then finally after 1 second we display a UIAlertView.
The problem is now that since the SSHUDViews are run asynchronously on a background thread when I get to display the UIAlertView the SSHUDViews have not finished displaying so the UIAlertView will overlay the hud.
Basically I need a way to queue up and delay methods whether they are of class SSHUDView or UIAlertView. A feedback queue, where you can delay individual messages.

Answer 1

What you're talking about sounds like a perfect fit for semaphores (see under the heading Using Dispatch Semaphores to Regulate the Use of Finite Resources)! I saw the SO Answer you linked to and I don't think it solves the case of UIView animations. Here's how I'd use semaphores.
In your view controller add an instance variable dispatch_semaphore_t _animationSemaphore; and initialize it in the - init method:
- (id)init
{
if ((self = [super init])) {
_animationSemaphore = dispatch_semaphore_create(1);
}
return self;
}
(Don't forget to release the semaphore in the - dealloc method using dispatch_release. You also might want to wait for queued animations to finish by using dispatch_semaphore_wait, but I'll leave that for you to figure out.)
When you want to queue up an animation, you'll do something like this:
- (void)animateSomething
{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0), ^{
dispatch_semaphore_wait(_animationSemaphore, DISPATCH_TIME_FOREVER);
dispatch_async(dispatch_get_main_queue(), ^{
[UIView animateWithDuration:0.5 animations:^{
// Your fancy animation code
} completion:^(BOOL finished) {
dispatch_semaphore_signal(_animationSemaphore);
}];
});
});
}
You can use the - animateSomething template to accomplish different things, such as displaying an SSHUDView or a UIAlertView.

Answer 2

What you're describing sounds like an animation. Why not just use UIView animation and chain the series of animation blocks:
[UIView animateWithDuration:2
animations:^{
// display first HUD
}
completion:^(BOOL finished){
[UIView animateWithDuration:2
animations:^{
// hide first HUD, display second HUD
}
completion:^(BOOL finished){
[UIView animateWithDuration:2
animations:^{
// hide second HUD, show UIAlert
}
completion:nil
];
}
];
}
];