accessing ivars in a block

gistfile1.m

#import <Foundation/Foundation.h>
#import "AFJSONRequestOperation.h"

@interface Data : NSObject {
    NSURLRequest *request;
    AFJSONRequestOperation *operation;
    id receiver;
    SEL action;
}

- (void)fetch;
- (Data *)initWithURL:(NSURL *)anURL forReceiver:(id)aReceiver andSelector:(SEL)aSelector;


@end

@implementation Data

@synthesize JSON;

- (Data *)initWithURL:(NSURL *)anURL  forReceiver:(id)aReceiver andSelector:(SEL)aSelector
{
    self = [super init];
    
    if (self) {
        selector = aSelector;
        receiver = aReceiver;
        
        // anURL used is [NSURL URLWithString:@"http://echo.jsontest.com/one/two"]
        request = [NSURLRequest requestWithURL:anURL];
        operation = nil;
    }
    return self;
}

- (Data *)init
{
    return [self initWithURL:nil forReceiver:nil andSelector:nil];
}

- (void)fetch
{
    void (^successHandler)(NSURLRequest *, NSHTTPURLResponse *, id) = ^(NSURLRequest *aRequest, NSHTTPURLResponse *aResponse, id returnedJSON)
    {
        NSLog(@"Data returned - %@", aResponse);
        [receiver performSelector:selector withObject:JSON withObject:self];
        JSON = returnedJSON;
        operation = nil;
    };
    
    operation = [AFJSONRequestOperation
                 JSONRequestOperationWithRequest:request
                 success:successHandler
                 failure:nil];
    [operation start];
}

@end