© 2013 James Montgomerie
jamie@montgomerie.net, http://www.blog.montgomerie.net/
jamie@th.ingsmadeoutofotherthin.gs, http://th.ingsmadeoutofotherthin.gs/

• Three easy ways to do things later in Cocoa/Cocoa Touch.
• Simpler than dispatch_after, -performSelector:withObject:afterDelay: and NSTimer

Three ways! All call back on the main thread/runloop/dispatch queue.

1. A Category on NSObject defines a -thIn: method that takes an NSTimeInterval and returns a proxy object. Methods sent to it will be queued and sent to the original object after the interval elapses. The recently new instancetype return type makes this type-safe too!

   [[self thIn:3] doYourThingWithThisArray:@[ @"Everybody", @"to", @"the", @"limit!" ]];

2. A Category on NSObject defines a -thIn:do: method that takes an NSTimeInterval and a block, and invokes the block after the interval elapses.

   [self thIn:3 do:^(id obj) { 
       NSLog(@"The passed in object is the same as self. It's weakly held: %@", obj);
   }];

3. THInWeakTimer is a lightweight timer. It has two main methods. -invalidate specifically cancels the timer. The timer is also implicitly cancelled if the THInWeakTimer is deallocated.

   @interface THInWeakTimer : NSObject
   - (id)initWithDelay:(NSTimeInterval)delay do:(void (^)(void))block;
   - (void)invalidate;
   @end

In the first two cases, the target object is weakly held. This means that if it is released before the interval is up the queued message/block will never be sent/invoked. Why? This is what made sense for my initial use case, and I still haven't found a case where I don't like the behaviour.

I've packaged this as a static library, you should be able to use it as detailed in this blog post. It's only a couple of files though, so I won't tell anyone if you just copy them into your project instead.