CODEWITHSUNDEEP
iosobjective-ccocoa-touchcocoansoperation
user1834305
user1834305

Reputation:

NSOperation dependent operation and dependent objects

I have two different NSOperation subclasses. One that downloads the feed from server and the other one to parse.

@interface FeedDownloader:NSOperation
 @property(nonatomic, strong) NSString *downloadedFeed;
@end

@interface FeedParser:NSOperation
 @property(nonatomic, strong) NSString *feedToParse;
@end

Then, in my "view controller", I add these operations to my NSOperationQueue and set dependency.

NSOperationQueue *queue = [[NSOperationQueue alloc] init];
FeedDownloader *downloader = [[FeedDownloader alloc] init];
FeedParser *parser = [[FeedParser alloc] init];
[parser addDependency:downloader];
[downloader addObserver:self forKeypath: @"isFinished" context:kDownloaderContext];
[queue addOperation:downloader];
[queue addOperation:parser];

Now, I get the "KVO notification" from the downloader that it finished downloading the feed. How could I pass the downloaded feed to the parser once the download completes and before it starts parsing.

Upvotes: 1

Views: 427

Answers (2)

Ken Thomases
Ken Thomases

Reputation: 90531

You could declare a protocol, maybe FeedProvider, which has a method by which a FeedParser can request a feed string. Make FeedDownloader adopt FeedProvider. Give FeedParser a provider property of type id <FeedProvider>. At creation time, give the parser object a reference to the downloader object as its provider.

Upvotes: 0

Paul.s
Paul.s

Reputation: 38728

In your FeedParser class you can ensure the the isReady is not true until it has the required data is set - this way the operation won't prematurely start until it has it's dependencies.

There are lots of ways to do this - the first thing that would come to mind for me is to use the completion block of the download operation

__weak __typeof(parser)     weakParser     = parser;
downloader.completionBlock = ^{
  weakParser.feedToParse = downloader.downloadedFeed;
};

Upvotes: 1

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