perform a block in a background thread, and call a completion block on the main thread when its done.

NSObject+RFExtensions.h

//
//  NSObject+RFExtensions.h
//
//  Created by brandon on 10/5/12.
//  Copyright (c) 2012 redf.net. All rights reserved.
//

#import <Foundation/Foundation.h>

typedef void (^NSObjectPerformBlock)(id userObject);

@interface NSObject (RFExtensions)

- (void)performBlockInBackground:(NSObjectPerformBlock)performBlock completion:(NSObjectPerformBlock)completionBlock userObject:(id)userObject;

@end

NSObject+RFExtensions.m

//
//  NSObject+RFExtensions.m
//
//  Created by brandon on 10/5/12.
//  Copyright (c) 2012 redf.net. All rights reserved.
//

#import "NSObject+RFExtensions.h"

@implementation NSObject (RFExtensions)

- (void)performBlockInBackground:(NSObjectPerformBlock)performBlock completion:(NSObjectPerformBlock)completionBlock userObject:(id)userObject
{
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        performBlock(userObject);
        dispatch_async(dispatch_get_main_queue(), ^{
            completionBlock(userObject);
        });
    });
}

@end