title: AFHTTPSessionManager block is not called when app is on background
body: <p>My app get a silent push, then do some http request in background using AFNetworking,but it didn't enter the complete block, code is:</p>
  
  <pre><code>AFHTTPSessionManager *manager = [[AFHTTPSessionManager alloc] init];
  [manager GET:urlString
    parameters:nil
       success:^(NSURLSessionDataTask *task, id responseObject) {
           NSLog(@"response objece:%@", responseObject);
       }
       failure:^(NSURLSessionDataTask *task, NSError *error) {
           NSLog(@"error:%@", error);
       }];
  </code></pre>
  
  <p>then I found maybe I could use NSURLSessionConfiguration to config the session:</p>
  
  <pre><code>NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration backgroundSessionConfiguration:@"com.company.backgroundDownloadSession"];
  AFHTTPSessionManager *manager = [[AFHTTPSessionManager alloc] initWithSessionConfiguration:configuration];
  [manager GET:urlString
    parameters:nil
       success:^(NSURLSessionDataTask *task, id responseObject) {
           NSLog(@"response objece:%@", responseObject);
       }
       failure:^(NSURLSessionDataTask *task, NSError *error) {
           NSLog(@"error:%@", error);
       }];
  </code></pre>
  
  <p>but AFNetworking crash says:'Terminating app due to uncaught exception 'NSGenericException', reason: 'Data tasks are not supported in background sessions.'
  What should I do? And I appreciate your help!</p>