Sending NSString to Server using the HTTP Post Method - Need Help!

In a nutshell, you have to use NSMutableURLRequest and NSURLSession (The NSURLSession sends the NSMutableURLRequest). First, create a new NSMutableURLRequest:

NSMutableURLRequest *req = [[NSMutableURLRequest alloc] initWithURL:[NSURL URLWithString:@"YOUR URL HERE"]];
[req setHTTPMethod:@"POST"];

Now, we need to attach the POST data (your NSString) to the NSMutableURLRequest. To do that, take your string (let's say it's called str) and convert it to NSData:

NSData *postData = [str dataUsingEncoding:NSASCIIStringEncoding allowLossyConversion:YES];

Then, we need to set the Content-Length header in the POST request (so your server knows how much content it's getting) and attach our post data to the request:

NSString *postLength = [NSString stringWithFormat:@"%d",[postData length]];
[req addValue:postLength forHTTPHeaderField:@"Content-Length"];
[req setHTTPBody:postData];

Now we're done configuring our NSMutableURLRequest! Next, we have to create an NSURLSession:

NSURLSession *session = [NSURLSession sharedSession];

Then, you should use the [-dataTaskWithRequest:completionHandler] method on NSURLSession to send the request and pass in a callback that you want to have executed when the response comes back. The way it works is you get an NSURLSessionDataTask back, and you just call [-resume] on it:

NSURLSessionDataTask *task = [session dataTaskWithRequest:req
                                            completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
                                                // Do something with response data here - convert to JSON, check if error exists, etc....
                                            }];

[task resume];

Now your request is sent, and your completionHandler will be called whenever you get a response!