Keep blocks inside a dictionary

I have my own method that takes a block as an argument. I want to keep track of that block inside an NSDictionary. What is the best way to add the block to the dictionary?

I tried this code but after executing the line below (setObject...) the dictionary is still empty. I presume that is because the block is not of type NSObject. But what is the right way to do this?

- (void)startSomething:(NSURLRequest*)request block:(void (^)(NSURLResponse*, NSData*, NSError*))handler {

    NSURLConnection *connection = [NSURLConnection connectionWithRequest:request delegate:self];

    [pendingRequests setObject:handler forKey:connection];
}

EDIT:

Never mind. I don't know what I was thinking. 3 points:

1. Blocks are objc objects
2. Typo: setObject should be setValue
3. forKey is a string so it should be [connection description] or something like that

Anyway I fixed my problem now like this:

- (void)startSomething:(NSURLRequest*)request block:(void (^)(NSURLResponse*, NSData*, NSError*))handler {

    NSURLConnection *connection = [NSURLConnection connectionWithRequest:request delegate:self];
    [pendingRequests setValue:handler forKey:[connection description]];
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {

    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(void) {

        void (^handler)(NSURLResponse*, NSData*, NSError*);
        handler = [pendingRequests valueForKey:[connection description]];
        handler(nil, nil, nil);
    });
}