How to wrap AFNetworking AFJSONRequestOperation into a separate datamanager class - ios

Question

I'm new to using blocks in iOS and I am thinking that's probably the crux of my problem.
I just want to build a simple static DataManager class whose sole job is to fetch data from my Restful service.
I would call this from all my various UIViewControllers (or collectionview/table controllers)
In my class i have a function that looks like this
+ (NSArray *) SearchByKeyword: (NSString*) keyword {
__block NSArray* searchResults = [[NSArray alloc] init];
NSString *baseURL = #"http://someURL.com/api/search";
NSString *requestURL = [baseURL stringByAppendingString:keyword];
AFHTTPClient *httpClient = [[AFHTTPClient alloc] initWithBaseURL:[NSURL URLWithString:baseURL]];
NSMutableURLRequest *request = [httpClient requestWithMethod:#"GET"
path:requestURL
parameters:nil];
AFJSONRequestOperation *operation = [AFJSONRequestOperation JSONRequestOperationWithRequest:request success:^(NSURLRequest *request, NSHTTPURLResponse *response, id JSON) {
searchResults = [JSON valueForKeyPath:#""];
} failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error, id JSON) {
NSLog(#"Request Failed with Error: %#, %#", error, error.userInfo);
}];
[operation start];
return searchResults;
}
However, this keeps returning zero data. Can someone suggest the right way of doing this?

Answer 1

You are trying to use the results of an asynchronous task (the JSON operation) as the return value for a synchronous method call, so that is why you get no data.
You could provide your view controllers with an API that takes completion blocks and failure blocks, similar to the AF networking one. View controllers can then do what they need to do with the results when they are passed into the block.
Modifying your code from your question:
typedef void (^SearchCompletionBlock)(NSArray *results);
typedef void (^SearchFailureBlock)(NSError *error);
+ (void)searchByKeyword:(NSString*)keyword completionBlock:(SearchCompletionBlock)completionBlock failureBlock:(SearchFailureBlock)failureBlock;
{
NSString *baseURL = #"http://someURL.com/api/search";
NSString *requestURL = [baseURL stringByAppendingString:keyword];
AFHTTPClient *httpClient = [[AFHTTPClient alloc] initWithBaseURL:[NSURL URLWithString:baseURL]];
NSMutableURLRequest *request = [httpClient requestWithMethod:#"GET"
path:requestURL
parameters:nil];
AFJSONRequestOperation *operation = [AFJSONRequestOperation JSONRequestOperationWithRequest:request
success:^(NSURLRequest *request, NSHTTPURLResponse *response, id JSON) {
if (completionBlock) {
completionBlockc([JSON valueForKeyPath:#""]);
}
} failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error, id JSON) {
NSLog(#"Request Failed with Error: %#, %#", error, error.userInfo);
if (failureBlock) {
failureBlock(error);
}
}];
[operation start];
}
Then clients could pass completion blocks that stored the results and reloaded their views. Something like:
^ (NSArray *results) {
self.results = results;
[self.tableView reloadData];
}

Answer 2

Your JSON request operation is asynchronous, meaning that it will kick off the request ([operations start], then immediately return your results, which will be empty. When the completion block runs, it assigns your data but nothing is done with it. Your search method can't return an object unless it waits for the request to complete.
You've got a few options:
Pass in a completion block to the search method which does something with the results. The completion block is called in the completion block of the request, once all the service-specific stuff (processing JSON etc) is finished. (Block inception!)
Have the completion block of the request assign a property of the data manager, then call a delegate method or notification to let others know the results are available.
I'd prefer option 1.