GCD convenience method for a long running task and a callback when it's done

Example.h

#import <UIKit/UIKit.h>

@interface Example : NSObject

- (void)performLongRunningTask:(SEL)taskMethod withCallback:(SEL)callbackMethod;

@end

Example.m

#import "Example.h"

@implementation

- (void)performLongRunningTask:(SEL)taskMethod withCallback:(SEL)callbackMethod
{
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0), ^()
                   {
                       [self performSelector:taskMethod];
                       
                       dispatch_async(dispatch_get_main_queue(), ^()
                                      {
                                          [self performSelector:callbackMethod];
                                      });
                   });
}

@end