取消单个操作：

AFHTTPRequestOperation *operation

     = [[AFHTTPRequestOperation alloc] initWithRequest:request];

[operation cancel];

或者

AFHTTPRequestOperation *operation

    = [postManager POST:request.methodUrl

             parameters:parameters

                success:^(AFHTTPRequestOperation *operation,

                          id responseObject) {

                          }failure:^(AFHTTPRequestOperation *operation,

                              NSError *error){

        }];

[operation cancel];

取消全部操作：

AFHTTPRequestOperationManager *httpmanager

    = [AFHTTPRequestOperationManager manager];

[httpManager.operationQueue cancelAllOperations];