Question

I have a singleton that I’m using to parse XML and then cache it. The parsing/caching is done with a block. Is there any way for me to pass an argument to this block from another class so that I can change the URL from outside the singleton?

Here’s the code I have now:

// The singleton
+ (FeedStore *)sharedStore
{
    static FeedStore *feedStore = nil;
    if(!feedStore)
        feedStore = [[FeedStore alloc] init];

    return feedStore;
}

- (RSSChannel *)fetchRSSFeedWithCompletion:(void (^)(RSSChannel *obj, NSError *err))block
{
    NSURL *url = [NSURL URLWithString:@"http://www.test.com/test.xml"];

    ...

    return cachedChannel;
}

And here’s the class where I need to modify the NSURL from:

- (void)fetchEntries
{
    [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:YES];

    // Initiate the request...

    channel = [[BNRFeedStore sharedStore] fetchRSSFeedWithCompletion:
           ^(RSSChannel *obj, NSError *err) {
        ...
    }
}

How do I pass an argument from fetchEntries to fetchRSSFeedWithCompletion?

Answer 1

You would want to add a parameter in the method, not the block.

Also, when using a completion block, there really is no reason to return anything in the method.

I’d change it to look like this:

-(void)fetchRSSFeed:(NSURL *)rssURL completion:(void (^)(RSSChannel *obj, NSError *error))block{
    RSSChannel *cachedChannel = nil;
    NSError *error = nil;

    // Do the xml work that either gets you a RSSChannel or an error

    // run the completion block at the end rather than returning anything
    completion(cachedChannel, error);
}