NSURLSession delegate vs. completionHandler

If you want to add a custom delegate class, you need to implement the NSURLSessionDataDelegate and NSURLSessionTaskDelegate protocols at the minimum.

With the methods:

NSURLSessionDataDelegate - get continuous status of your request

 - (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveResponse:(NSURLResponse *)response completionHandler:(void (^)(NSURLSessionResponseDisposition disposition))completionHandler {    receivedData=nil; receivedData=[[NSMutableData alloc] init];    [receivedData setLength:0];    completionHandler(NSURLSessionResponseAllow);}

NSURLSessionDataDelegate

-(void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask   didReceiveData:(NSData *)data {    [receivedData appendData:data];}

NSURLSessionTaskDelegate

 - (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)taskdidCompleteWithError:(NSError *)error { if (error) {  // Handle error }else {   NSDictionary* response=(NSDictionary*)[NSJSONSerialization JSONObjectWithData:receivedData options:kNilOptions error:&tempError];    // perform operations for the  NSDictionary response}

If you want to separate the delegate code (middle layer) from your calling class (generally its good practice to have separate class/layer for network calls), the delegate of NSURLSession has to be :-

NSURLSession *session=[NSURLSession sessionWithConfiguration:sessionConfig delegate:myCustomDelegateClass delegateQueue:nil];

Ref Links:

1. NSURLSession Class Reference
2. iOS NSURLSession Example (HTTP GET, POST, Background Downlads )
3. From NSURLConnection to NSURLSession