Saving a block in instance variable

Question

How do we declare a global(private instance variable) to accept a block in it. Do we need to synthesis it & what are the memory management implications with it.

Answer 1

Here's an (ARC-less) example of storing a block for a completion callback after doing some work in the background:

Worker.h:

@interface Worker : NSObject
{
    void (^completion)(void);
}
@property(nonatomic,copy) void (^completion)(void);
- (void)workInBackground;
@end

Worker.m:

@implementation Worker
@synthesize completion;

- (void)dealloc
{
    Block_release(completion);

    [super dealloc];
}

- (void)setCompletion:(void (^)(void))block
{
    if ( completion != NULL )
        Block_release(completion);

    completion = Block_copy(block);
}

- (void)workInBackground
{
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(void)
    {
        // Do work..

        dispatch_async(dispatch_get_main_queue(), completion);
    });
}

@end