NSURLSessionUploadTask as separate method, but returning data to a call

Question

Undoubtedly, people will shake their head in shame at the following, but I would appreciate the help.

I seem to make the same calls to NSURLSessionUploadTask with pretty much the same structure throughout the program. Hence, I am trying to make it a method which I can call from anywhere in the program and, when it's complete, return the NSDictionary to the call which made it.

Currently I have the following:

-(NSDictionary *)serverRequest:(NSString *)requestURL withDictionary:(NSDictionary *)sendDict {

    NSURL *homeURL = [[NSURL alloc] initWithString:[NSString stringWithFormat:@"%@/%@",baseURL, requestURL]];
    NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL:homeURL];
    [request setHTTPMethod:@"POST"];
    [request addValue:@"application/json" forHTTPHeaderField:@"Content-Type"];
    [request addValue:@"application/json" forHTTPHeaderField:@"Accept"];
    [request setCachePolicy:NSURLCacheStorageAllowedInMemoryOnly];

    NSData *sentData = [NSJSONSerialization dataWithJSONObject:sendDict options:0 error:nil];

    NSURLSessionUploadTask *uploadTask = [_session uploadTaskWithRequest:request fromData:sentData completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {

        returnedData = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingAllowFragments error:nil];

        if ([returnedData[@"code"] isEqualToString:@"OK"])
        {
            dispatch_async(dispatch_get_main_queue(), ^{

                return returnedData;

            });
        }


    }];

    [uploadTask resume];

}

So I pass in the URL I want to call, and the NSDictionary which is then sent to the server. The server replies, with a JSON response, which I then turn into returnedData. I simply wish to pass this data back to the call which made it ... something like:

NSDictionary *mydata = @{@"email": userRegisterTextFieldEmailAddress.text};
NSDictionary *passedBackData = [self serverRequest:@"checkUserName" withDictionary:mydata];

When I try this it won't build as the dispatch_async isn't the right format etc, etc. I have tried to read up on this, and can't believe it's a hard problem? Surely others aren't making the same call with the same code each time they want to return some data from a web server?

Thanks in advance for any help you can give in clearing up my misunderstanding.

Answer 1

What you'd generally do is add a completion block parameter to your method, that specifies what you want to do upon receiving the response. So, add a block parameter to your method and add the code that calls that block, something like:

- (void) serverRequest:(NSString *)requestURL withDictionary:(NSDictionary *)sendDict completion:(void (^)(id responseObject, NSError *error))completion
{
    NSURL *homeURL = [[NSURL alloc] initWithString:[NSString stringWithFormat:@"%@/%@", baseURL, requestURL]];
    NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL:homeURL];
    [request setHTTPMethod:@"POST"];
    [request addValue:@"application/json" forHTTPHeaderField:@"Content-Type"];
    [request addValue:@"application/json" forHTTPHeaderField:@"Accept"];
    [request setCachePolicy:NSURLCacheStorageAllowedInMemoryOnly];

    NSData *sentData = [NSJSONSerialization dataWithJSONObject:sendDict options:0 error:nil];

    NSURLSessionUploadTask *uploadTask = [_session uploadTaskWithRequest:request fromData:sentData completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {

        // report any network-related errors

        if (!data) {
            if (completion) {
                dispatch_async(dispatch_get_main_queue(), ^{
                    completion(nil, error);
                });
            }
            return;
        }

        // report any errors parsing the JSON

        NSError *parseError = nil;
        returnedData = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingAllowFragments error:nil];

        if (!returnedData) {
            if (completion) {
                dispatch_async(dispatch_get_main_queue(), ^{
                    completion(nil, parseError);
                });
            }
            return;
        }

        // if everything is ok, then just return the JSON object

        if (completion) {
            dispatch_async(dispatch_get_main_queue(), ^{
                completion(returnedData, nil);
            });
        }
    }];

    [uploadTask resume];
}

You'd then call this serverRequest method, specifying precisely what you want to do with the data you receive:

[self serverRequest:url withDictionary:dictionary completion:^(id responseObject, NSError *error) {
    if (responseObject) {
        // do what you want with the response object here
    } else {
        NSLog(@"%s: serverRequest error: %@", __FUNCTION__, error);
    }
}];

Clearly, you can change this as you see fit, but hopefully this illustrates the idea. If, for example, you knew that responseObject was always going to be a NSDictionary, then I'd change the references to id responseObject with NSDictionary *responseObject.

But the idea is that you should just provide a block that takes the response data and/or the error as parameters. That way, the code that calls this method can specify what should happen when the asynchronous network request completes.