Couple of typedefs that I think make the NSFilePresenter block APIs a little easier to read

gistfile1.m

typedef void (^FilePresenterReacquirerBlock)(void);
typedef void (^FilePresenterReaderBlock)(FilePresenterReacquirerBlock reacquirer);
typedef void (^FilePresenterWriterBlock)(FilePresenterReacquirerBlock reacquirer);
typedef void (^FilePresenterCompletionHandler)(NSError *errorOrNil);

- (void)relinquishPresentedItemToReader:(FilePresenterReaderBlock)reader
{
    // Do stuff here ahead of reading
    reader(^{
        // Do stuff here after reading is done
    });
}

- (void)relinquishPresentedItemToWriter:(FilePresenterWriterBlock)writer
{
    // Do stuff here ahead of writing
    writer(^{
        // Do stuff here for after writing is done
    });
}

- (void)savePresentedItemChangesWithCompletionHandler:(FilePresenterCompletionHandler)completionHandler
{
    completionHandler(nil);
}

- (void)accommodatePresentedItemDeletionWithCompletionHandler:(FilePresenterCompletionHandler)completionHandler
{
    completionHandler(nil);
}