Execute a method synchronously after a NSURLSession - ios

Question

I'm currently trying to execute a method after a NSURLSession completes. The problem is I can't manage in any way the asynchronous nature of its object. I've tried with GCD and NSOperation as suggested in the other questions but nothing changes: after the initialization with dataTaskWithRequest:completionHandeler:, the application starts executing the next method in the program.
Here is the method which realizes the networking:
-(void)sendData{
NSData *JSONdata = [NSJSONSerialization dataWithJSONObject:userInfoToJSON options:0 error:&error];
NSURL *url = [NSURL URLWithString:#"http://mobdev2015.com/register.php"];
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
NSString *postLength = [NSString stringWithFormat:#"%lu", (unsigned long)[JSONdata length]];
[request setHTTPMethod:#"POST"];
[request setValue:#"application/json" forHTTPHeaderField:#"Accept"];
[request setValue:#"application/json" forHTTPHeaderField:#"Content-Type"];
[request setValue:postLength forHTTPHeaderField:#"Content-Length"];
[request setHTTPBody:JSONdata];
[[session dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
requestReply = [[NSString alloc] initWithData:data encoding:NSASCIIStringEncoding];
}]resume];
});
}
Here is the method instead which calls the one above and where I want to implement a synchronous execution:
-(void)MethodWhichNeedsToBeSync{
//Creating a JSON object..
[self sendData:userInfoToJSON];
//MethodB wants to be executed if and only if sendData is completed
[self MethodB];
}
Thank you for the replies.

Answer 1

The way to execute a method after the completion of an asynchronous method is to have that method called in the completion block (or closure) of the asynchronous method.
For your case, it would look something like this:
[[session dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
requestReply = [[NSString alloc] initWithData:data encoding:NSASCIIStringEncoding];
if (!error) {
[self MethodB];
}
}]resume];
});
where the call to be run after successful completion of the asynchronous method is moved into the completion handler.
That would accomplish the execution of MethodB if and only if sendData is completed, as you wanted.

Answer 2

As far as I can tell from the NSURLSession documentation there's no way to use it to make synchronous requests. I assume that's because you really shouldn't be making calls that could block the main queue.
However, if using NSURLSession isn't required you can simply use NSURLConnection instead. You would initialize it with your request and call "sendSynchronousRequest:returningResponse:".