AsyncBlockOperation by XibXor.com http://xibxor.com/objective-c/asynchronous-block-operations/

AsyncBlockOperation.h

//
//  AsyncBlockOperation.h
//
//  Created by XibXor.com on 4/29/13.
//
//

#import <Foundation/Foundation.h>

@class AsyncBlockOperation;
typedef void (^td_async_block_operation_opblock)(AsyncBlockOperation* op);



@interface AsyncBlockOperation : NSOperation

@property (atomic, assign) BOOL isExecuting;
@property (atomic, assign) BOOL isFinished;

@property (atomic, strong) td_async_block_operation_opblock executionBlock;




+ (id) blockOperationWithBlock:(td_async_block_operation_opblock) block;

- (id) initWithBlock:(td_async_block_operation_opblock) block;
- (void) complete;


@end

AsyncBlockOperation.m

//
//  AsyncBlockOperation.m
//
//  Created by XibXor.com on 4/29/13.
//
//

#import "AsyncBlockOperation.h"

@interface AsyncBlockOperation()
@end


@implementation AsyncBlockOperation

+ (id) blockOperationWithBlock:(td_async_block_operation_opblock) block {
    return [[self alloc] initWithBlock:block];
}


- (id) initWithBlock:(td_async_block_operation_opblock) block {
    self = [self init];
    _executionBlock = block;

    return self;
}

- (void) start {
    if (_executionBlock){
        // set status properties and fire off KVO
        [self setIsRunning:YES];
        
        // execute the block, passing self for completion
        _executionBlock(self);
        
        // release the execution block after execution
        _executionBlock = nil;
    }else {
        [self complete];
    }
}

- (void) complete {
    // release the execution block
    _executionBlock = nil;
    
    // set status properties and fire off KVO
    [self setIsRunning:NO];
}

- (void) setIsRunning: (BOOL) isRunning {
    
    [self willChangeValueForKey:@"isExecuting"];
    [self willChangeValueForKey:@"isFinished"];
    self.isFinished = !(self.isExecuting = isRunning);
    [self didChangeValueForKey:@"isExecuting"];
    [self didChangeValueForKey:@"isFinished"];
    
}

@end

AsyncBlockOperation.README.txt

AsyncBlockOperation is very similar to NSBlockOperation with one caveat; the block you pass to it receives one argument, a reference to the AsyncBlockOperation for the block. When your block is done with its task, it must call [op complete]


Example usage:

NSOperation* asyncOp = [AsyncBlockOperation blockOperationWithBlock:^(AsyncBlockOperation* op) {
    NSLog(@"starting op");
    double delayInSeconds = 2.0;
    dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
    dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
        if (op.isCancelled){
            return [op complete];
        }
        
        NSLog(@"2 seconds have passed");
        NSLog(@"calling [op complete]");
        [op complete];
    });
    NSLog(@"op block returns but op isn't finished");
}];
asyncOp.completionBlock = ^{
    NSLog(@"completion block called!");
};
[asyncOp start];



Output in terminal will be:
2013-04-29 22:51:57.417 Experiments[5795:11603] starting op
2013-04-29 22:51:57.419 Experiments[5795:11603] op block returns but op isn't finished
2013-04-29 22:51:59.420 Experiments[5795:11603] 2 seconds have passed
2013-04-29 22:51:59.421 Experiments[5795:11603] calling [op complete]
2013-04-29 22:51:59.422 Experiments[5795:12e03] completion block called!