Returning a BOOL method inside a block?

Question

I have this bool method that returns a yes or no for an inputted string. I'm successfully able to return a YES or a NO, but I cannot seem to able to make a network connection and return a YES or a NO depending on the server's response. I tried using __block and I don't feel like that will wait for the web request to finish, is there a way to return YES or NO in the success block without it giving me the error:

Incompatible block pointer types sending 'BOOL(^)(NSURLSessionTask*__strong, NSError __strong' to parameter of the type 'void(^)(NSURLSessionTask...)

-(BOOL)customResponseForString:(NSString *)text {

  __block BOOL response_available;

  dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    AFHTTPSessionManager *manager = [AFHTTPSessionManager manager];
    manager.responseSerializer = [AFHTTPResponseSerializer serializer];
    [manager.responseSerializer setAcceptableContentTypes:[NSSet setWithObject:@"text/plain"]];
    [manager GET:[NSString stringWithFormat:@"http://example.com/response.php?input=%@", text] parameters:nil success:^(NSURLSessionDataTask *task, id responseObject) {

        NSDictionary *response = [NSJSONSerialization JSONObjectWithData:responseObject options:NSUTF8StringEncoding error:nil];
        response_available = (BOOL)response[@"response_available"];
        if (response_available) {
            [session sendTextSnippet:response[@"response"] temporary:NO scrollToTop:NO dialogPhase:@"Summary"];
        } else {
            response_available = NO;
        }

        [session sendTextSnippet:[[NSString alloc] initWithData:responseObject encoding:NSUTF8StringEncoding] temporary:NO scrollToTop:NO dialogPhase:@"Summary"];

        [session sendRequestCompleted];

    } failure:^(NSURLSessionDataTask *task, NSError *error) {
        //return NO;
    }];
 });

return response_available;

}

Answer 1

Your block definition syntax is probably erroneous, because you can definitely return a BOOL along other parameters in a block.

- (void)fetchCurrentUserWithCompletion:(void (^)(BOOL success, User *user))completion;

This method would be called like this:

[self.userProfileController fetchCurrentUserWithCompletion:^(BOOL success, User *user) {
    if (success) {
        NSLog(@"Current User Name: %@", user.fullName);
    }
}];

If you use AFNetworking, check the AFHTTPRequestOperation object that handle completionBlocks:

[requestOperation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
    User *user = [self userFromResponseObject:responseObject];   
    if (completion) completion(YES, user);
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
    if (completion) completion(NO, user);
}];

Answer 2

Because you are implicitly initializing response_available to NO and then using an async GCD call, your method as written will always immediately return NO without waiting for the request to finish. Note: switching to dispatch_sync won't help either because AFNetworking will queue the GET request asynchronously either way.

---

Best Approach

Add a completion block argument to customResponseForString:. Then simply execute your completion block in the success or failure blocks of the AFHTTPRequestOperation.

---

Workable Approach (use caution!)

It is possible to make customResponseForString: wait for a response to the network request, but you will have significant issues if it is ever called from the main thread.

First you create a dispatch group and tell it you are starting some long-running work:

dispatch_group_t networkGroup = dispatch_group_create();
dispatch_group_enter(networkGroup);

Then you need to make your network request and when it completes tell the group that the work is finished with dispatch_group_leave():

[manager GET:[NSString stringWithFormat:@"http://example.com/response.php?input=%@", text] parameters:nil success:^(NSURLSessionDataTask *task, id responseObject) {

    NSDictionary *response = [NSJSONSerialization JSONObjectWithData:responseObject options:NSUTF8StringEncoding error:nil];
    response_available = (BOOL)response[@"response_available"];
    if (response_available) {
        [session sendTextSnippet:response[@"response"] temporary:NO scrollToTop:NO dialogPhase:@"Summary"];
    } else {
        response_available = NO;
    }

    [session sendTextSnippet:[[NSString alloc] initWithData:responseObject encoding:NSUTF8StringEncoding] temporary:NO scrollToTop:NO dialogPhase:@"Summary"];

    [session sendRequestCompleted];

    dispatch_group_leave(networkGroup);

} failure:^(NSURLSessionDataTask *task, NSError *error) {
    response_available = NO;
    dispatch_group_leave(networkGroup);
}];

Before your original method returns, tell it to wait for the entire group to finish processing:

dispatch_group_wait(networkGroup, DISPATCH_TIME_FOREVER);
return response_available;

You could adjust this time interval as needed or leave it at DISPATCH_TIME_FOREVER to let the network request time out on its own.