A convenience function for dispatching blocks after a delay, with the ability to cancel them.
A little more info about the impetus for this code can be found in a blog post here: http://www.ultrajoke.net/2011/12/cancel-dispatch_after/
The code is wrapped up in a project so it can be seen used in an example, but if you aren't interested in all the fluff, just grab the SpacemanBlocks.h file
Unlike using dispatch_after, perform_block_after_delay returns a handle that allows the execution of the block to be canceled at any time. Canceling a delayed block causes it to be released, allowing for the immediate freeing of memory potentially retained by objects within the delayed block.
perform_block_after_delay returns a SMDelayedBlockHandle block, typedef'd as follows:
typedef void(^SMDelayedBlockHandle)(BOOL cancel);
If the returned handle is executed with it's argument set to YES, the execution of the delayed block is canceled, and the original block is released. If the returned handle is executed with it's argument set to NO, the delayed block is executed immediately and released - it will no longer be executed after the initially provided delay.
If a delayed block is expected to be canceled, it's handle should be retained for use at a later time. When this is the case, it is desirable to have the delayed block cleanup the out of date handle, there is a little bit of block juggling that needs to happen here.
@interface SMViewController : UIViewController
{
__block SMDelayedBlockHandle _delayedBlockHandle;
}
@end
@implementation SMViewController
- (void)delayBlock
{
SMDelayedBlockHandle handle = perform_block_after_delay(2.0f, ^{
// Work
[_delayedBlockHandle release];
_delayedBlockHandle = nil;
});
_delayedBlockHandle = [handle retain];
}
- (void)cancelBlock
{
if (nil == _delayedBlockHandle) {
return;
}
_delayedBlockHandle(YES);
[_delayedBlockHandle release];
_delayedBlockHandle = nil;
}
@end
Copyright (C) 2011 by Spaceman Labs
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