Take action after several asynchronous NSURLConnections have all completed [duplicate] - ios

Question

I have multiple operations (they're AFNetworking requests) with completion blocks that takes some time to execute, and a Core Data object that needs to be saved at the end of all the requests.
MyCoreDataObject *coreDataObject;
AFHTTPRequestOperation *operation1 = [[AFHTTPRequestOperation alloc] initWithRequest:request1];
[operation1 setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
coreDataObject.attribute1 = responseObject;
sleep(5);
}];
[operation1 start];
AFHTTPRequestOperation *operation2 = [[AFHTTPRequestOperation alloc] initWithRequest:request1];
[operation2 setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
coreDataObject.attribute2 = responseObject;
sleep(10);
}];
[operation1 operation2];
[context save:nil];
Of course, this does not work as I want because the requests are asynchronous. I tried adding an NSOperationQueue like so:
NSOperationQueue *operationQueue = [[NSOperationQueue alloc] init];
[operationQueue setMaxConcurrentOperationCount:2];
AFHTTPRequestOperation *operation1 = [[AFHTTPRequestOperation alloc] initWithRequest:request1];
[operation1 setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
coreDataObject.attribute1 = responseObject;
sleep(5);
}];
[operationQueue addOperation:operation1];
AFHTTPRequestOperation *operation2 = [[AFHTTPRequestOperation alloc] initWithRequest:request1];
[operation2 setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
coreDataObject.attribute2 = responseObject;
sleep(10);
}];
[operationQueue addOperation:operation2];
[imageQueue waitUntilAllOperationsAreFinished];
[context save:nil];
This looks a bit better. Using waitUntilAllOperationsAreFinished, my queue blocks the current thread until my requests are finished, but not until my success Blocks are finished, which is really what I need.
Any ideas on how to achieve this in a good way?

Answer 1

Use dispatch groups.
dispatch_group_t group = dispatch_group_create();
MyCoreDataObject *coreDataObject;
dispatch_group_enter(group);
AFHTTPRequestOperation *operation1 = [[AFHTTPRequestOperation alloc] initWithRequest:request1];
[operation1 setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
coreDataObject.attribute1 = responseObject;
sleep(5);
dispatch_group_leave(group);
}];
[operation1 start];
dispatch_group_enter(group);
AFHTTPRequestOperation *operation2 = [[AFHTTPRequestOperation alloc] initWithRequest:request1];
[operation2 setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
coreDataObject.attribute2 = responseObject;
sleep(10);
dispatch_group_leave(group);
}];
[operation2 start];
dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
dispatch_release(group);
[context save:nil];

Answer 2

AFNetworking has designed method for this kind of operations, which abstracts from GCD:
-enqueueBatchOfHTTPRequestOperationsWithRequests:progressBlock:completionBlock:
-enqueueBatchOfHTTPRequestOperations:progressBlock:completionBlock:
Take a look at FAQ

Answer 3

I belive something like this:
NSMutableArray *mutableOperations = [NSMutableArray array];
for (NSURL *fileURL in filesToUpload) {
NSURLRequest *request = [[AFHTTPRequestSerializer serializer] multipartFormRequestWithMethod:#"POST" URLString:#"http://example.com/upload" parameters:nil constructingBodyWithBlock:^(id<AFMultipartFormData> formData) {
[formData appendPartWithFileURL:fileURL name:#"images[]" error:nil];
}];
AFHTTPRequestOperation *operation = [[AFHTTPRequestOperation alloc] initWithRequest:request];
[mutableOperations addObject:operation];
}
NSArray *operations = [AFURLConnectionOperation batchOfRequestOperations:#[...] progressBlock:^(NSUInteger numberOfFinishedOperations, NSUInteger totalNumberOfOperations) {
NSLog(#"%lu of %lu complete", numberOfFinishedOperations, totalNumberOfOperations);
} completionBlock:^(NSArray *operations) {
NSLog(#"All operations in batch complete");
}];
[[NSOperationQueue mainQueue] addOperations:operations waitUntilFinished:NO];
refering to docs: http://cocoadocs.org/docsets/AFNetworking/2.5.0/

Answer 4

My requirements were those of do many request from an array of String (URL)
func updateSourceData(element: Int) {
if element > availableUrls.count - 1 {
return
}
let service = SourceDataServiceDao()
let currentUrl = availableUrls[element]
service.fooCall(url: currentUrl, completion: { (response, error) -> Void in
self.updateSourceData(element + 1)
})
}
Obviously, in this way calls are made in cascade, not N asynchronous calls.