Switched over to using in the operation subclass

Author: wibosco

NetworkingInOperations-Example/Data/Abstract/ConcurrentOperation.swift

@@ -62,11 +62,16 @@ class ConcurrentOperation<T>: Operation {
     // MARK: - Control
 
     override func start() {
-        super.start()
+        guard !isCancelled else {
+            finish()
+            return
+        }
 
         if !isExecuting {
             state = .executing
         }
+        
+        main()
     }
 
     func finish() {
@@ -77,8 +82,10 @@ class ConcurrentOperation<T>: Operation {
 
     func complete(result: DataRequestResult<T>) {
         finish()
-        
-        completionHandler?(result)
+    
+        if !isCancelled {
+            completionHandler?(result)
+        }
     }
 
     override func cancel() {

NetworkingInOperations-Example/Data/Managers/Questions/Operations/QuestionsRetrievalOperation.swift

@@ -23,9 +23,9 @@ class QuestionsRetrievalOperation: ConcurrentOperation<QuestionPage> {
         self.urlRequestFactory = urlRequestFactory
     }
 
-    // MARK: - Start
+    // MARK: - Main
 
-    override func start() {
+    override func main() {
         let urlRequest = urlRequestFactory.requestToRetrieveQuestions(pageIndex: pageIndex)
 
         task = session.dataTask(with: urlRequest) { (data, response, error) in

NetworkingInOperations-Example/Data/Managers/User/Operations/AvatarRetrievalOperation.swift

@@ -22,9 +22,9 @@ class AvatarRetrievalOperation: ConcurrentOperation<(User, UIImage)>  {
         self.user = user
     }
 
-    // MARK: - Start
+    // MARK: - Main
 
-    override func start() {
+    override func main() {
         guard let avatarURL = URL(string: user.avatarURL) else {
             cancel()
             return