iOS - How to increase variable in block using cycle - ios

Question

I need to create an entity on the server and then upload few images to the server.
So first block display success creating entity on the server then I starting upload 10 images one by one in cycle, but the app send the notification not after last 10 image was uploaded, so 'i' variable can be 10 even not be a 10 in the order. I am not sure but seems iteration in the block is not right. So I just want to be sure that the 10 images was uploaded and just then invoke sending notification.
So I skip some blocks parameters and failure options, array that I use for getting images to upload and etc. Just think about my blocks as an example that display success invocation after '{'.
// success first block
block1
{
// cycle from 0 to 10
for (NSInteger i = 0; i <=10; i++)
{
// success upload image to the server block
block2
{
// if I did 10 uploads I need to send notification.
if (i == 10)
{
// send notification here when last block returned success....
}
}
}
}

Answer 1

If you're creating a bunch of AFHTTPRequestOperation objects, then the most logical approach would be to create a completion operation and make it dependent upon the request operations:
NSOperation *completionOperation = [NSBlockOperation blockOperationWithBlock:^{
// code to be run when the operations are all done should go here
}];
for (...) {
// create `operation` AFHTTPRequestOperation however you want and add it to some queue
// but just make sure to designate the completion operation dependency
[completionOperation addDependency:operation];
}
// now that all the other operations have been queued, you can now add the completion operation to whatever queue you want
[[NSOperationQueue mainQueue] addOperation:completionOperation];

Answer 2

You can use Dispatch Group as the following.
// success first block
block1
{
dispatch_group_t group = dispatch_group_create();
// cycle from 0 to 10
__block NSUInteger successCount = 0;
for (NSInteger i = 0; i <=10; i++)
{
dispatch_group_enter(group);
// upload image to the server block
successOrErrorBlock
{
if (success)
successCount++;
dispatch_group_leave(group);
}
}
dispatch_group_notify(group, dispatch_get_main_queue(), ^{
if (successCount == 10) {
// send notification here when last block returned success....
}
});
}

Answer 3

The pattern I follow when invoking more than a couple blocks asynchronously is to create a to-do list (array) and perform that list recursively, like this:
// say this is our asynch operation. presume that someParameter fully
// describes the operation, like a file to be uploaded
- (void)performSomeAsynchOperationDefinedBy:(id)someParameter completion:(void (^)(BOOL, NSError *))completion {
// this could wrap any operation, like anything from AFNetworking
}
- (void)doOperationsWithParameters:(NSArray *)parameters completion:(void (^)(BOOL, NSError *))completion {
if (!parameters.count) return completion(YES, nil);
id nextParameter = someParameters[0];
NSArray *remainingParameters = [parameters subarrayWithRange:NSMakeRange(1, parameters.count-1)];
[self performSomeAsynchOperationDefinedBy:nextParameter completion:^(BOOL success, NSError *error)) {
if (!error) {
[self doManyOperations:remainingParameters completion:completion];
} else {
completion(NO, error);
}
}];
}
Now, to do several operations, place the parameters in an array, like:
NSArray *parameters = #[#"filename0", #"filename1", ...];
[self doOperationsWithParameters:parameters completion:(BOOL success, NSError *error) {
NSLog(#"ta-da!");
}];
A variant on the above with a progress block invoked up front and after each recursion (with a progress percentage initialCount/remainingCount) should be straight forward from the example provided.
Another variation would be to wrap both the param array and the completion block in a single NSObject, so the recursive call could be made with performSelector:, the benefit of doing this would be to not wind up the stack on a long recursion.