ios - AFNetworking 3.0 AFHTTPSessionManager using NSOperation

Question

I'm stuck now some time and I need help. So in AFNetworking 2.0 we have AFHTTPRequestOperation so I could easily use NSOperationQueue and have some dependencies. So what we have now is only AFHTTPSessionManagerand NSURLSession that does not subclass NSOperation. I have class APIClient that subclasses AFHTTPSessionManager. I am using that class as singleton as sharedClient. I have overriden GET and POST so for example GET looks this:

- (NSURLSessionDataTask *)GET:(NSString *)URLString
               parameters:(NSDictionary *)parameters
                  success:(void (^)(NSURLSessionDataTask *task, id responseObject))success
                  failure:(void (^)(NSURLSessionDataTask *task, NSError *error))failure {
NSURLSessionDataTask *task = [super GET:URLString parameters:parameters success:^(NSURLSessionDataTask *task, id responseObject) {
    success(task, responseObject);
} failure:^(NSURLSessionDataTask *task, NSError *error) {
    failure(task, [Response createErrorWithAFNetworkingError:error]);
}];

return task;
}

Do you have any idea how to implement in that manner (if it's possible) to wrap that as NSOperation? So what I want to do - I want to be able to run in parallel two network calls, and after that have another method call that depends on second network call of first two calls. Do you have any idea what would be best approach?

Answer 1

I've written a quick little set of classes (https://github.com/robertmryan/AFHTTPSessionOperation/) that wrap AFHTTPSessionManager requests in asynchronous NSOperation subclass. You can then use that to enjoy maxConcurrentOperation constraints, or operation dependencies.

For example, here's an example where we issue two concurrent requests and have a completion operation dependent upon completion of both of those requests:

//  ViewController.m

#import "ViewController.h"
#import "AFNetworking.h"
#import "AFHTTPSessionOperation.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    NSString *urlString1 = @"...";
    NSString *urlString2 = @"...";

    AFHTTPSessionManager *manager = [AFHTTPSessionManager manager];

    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    queue.name = @"AFHTTPSessionManager queue";

    NSOperation *completionOperation = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"All done");
    }];

    NSOperation *op1 = [AFHTTPSessionOperation operationWithManager:manager HTTPMethod:@"GET" URLString:urlString1 parameters:nil uploadProgress:nil downloadProgress:nil success:^(NSURLSessionDataTask *task, id responseObject) {
        NSLog(@"finished 1");
    } failure:^(NSURLSessionDataTask *task, NSError *error) {
        NSLog(@"failed 1 - error = %@", error.localizedDescription);
    }];
    [completionOperation addDependency:op1];

    NSOperation *op2 = [AFHTTPSessionOperation operationWithManager:manager HTTPMethod:@"GET" URLString:urlString2 parameters:nil uploadProgress:nil downloadProgress:nil success:^(NSURLSessionDataTask *task, id responseObject) {
        NSLog(@"finished 2");
    } failure:^(NSURLSessionDataTask *task, NSError *error) {
        NSLog(@"failed 2 - error = %@", error.localizedDescription);
    }];
    [completionOperation addDependency:op2];

    [queue addOperations:@[op1, op2] waitUntilFinished:false];
    [[NSOperationQueue mainQueue] addOperation:completionOperation];  // do this on whatever queue you want, but often you're updating UI or model objects, in which case you'd use the main queue
}

@end

It's worth noting that since you're only dealing with two requests, you could also use dispatch groups to accomplish the same thing:

//  ViewController.m

#import "ViewController.h"
#import "AFNetworking.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    NSString *urlString1 = @"...";
    NSString *urlString2 = @"...";

    AFHTTPSessionManager *manager = [AFHTTPSessionManager manager];

    dispatch_group_t group = dispatch_group_create();

    dispatch_group_enter(group);
    [manager GET:urlString1 parameters:nil progress:nil success:^(NSURLSessionDataTask * _Nonnull task, id  _Nullable responseObject) {
        NSLog(@"finished 1");
        dispatch_group_leave(group);
    } failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
        NSLog(@"failed 1 - error = %@", error.localizedDescription);
        dispatch_group_leave(group);
    }];

    dispatch_group_enter(group);
    [manager GET:urlString2 parameters:nil progress:nil success:^(NSURLSessionDataTask * _Nonnull task, id  _Nullable responseObject) {
        NSLog(@"finished 2");
        dispatch_group_leave(group);
    } failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
        NSLog(@"failed 2 - error = %@", error.localizedDescription);
        dispatch_group_leave(group);
    }];

    dispatch_group_notify(group, dispatch_get_main_queue(), ^{
        NSLog(@"All done");
    });
}

@end

With dispatch groups, you just need to be careful that every path within both the success and failure blocks call dispatch_group_leave.