Same reference for all the objects in iOS swift - ios

Question

In swift 4.2 I am facing the problem while handling the two array objects, When I am removing objects from another array, the values are removed from the all the objects.
1) Below is my closure
func GetChatBotData(completion: #escaping (_ result: ChatV_1_Model) -> Void) {
var ChatBotData : ChatV_1_Model! = nil
ApiHelper.sharedSession.postLoacl("http://localhost:3000/posts/", postData: NSDictionary(), methodtype: Constant.API.httpGet) { (isError, data, errorDescription) in
DispatchQueue.main.async(execute: {
if isError == false {
ChatBotData = ChatV_1_Model.init(fromDictionary: data!)
completion(ChatBotData)
}
else {
//completion("Error to get result" as AnyObject)
completion(ChatBotData)
}
})
}
}
Now In my controller
var PKComponents = [Chatbot_V_1_DataModel]()
var ChatMessages = [Chatbot_V_1_DataModel]()
override func viewDidLoad() {
super.viewDidLoad()
GetChatBotData() {(result: ChatbotV_1_Model!) in
print("Call Plans: \(result!)")
self.PKComponents = result.data
self.ChatMessages = result.data
self.ChatMessages[0].component.removeAll()
}
In Viewdidload I am removing objects from self.ChatMessages array but it removes from all the objects like, PKComponents and result.data as well.
Note: I have seen the reference of the result is same as PKComponents and Chatmessages.
How to resolve this?

Answer 1

Here's the simplified example, where I can reproduce your problem:
class Component {
}
class SomeData {
var components: [Component]
init(components : [Component]) {
self.components = components
}
}
class Result {
var data: [SomeData]
init(data: [SomeData]) {
self.data = data
}
}
let someData = SomeData(components: [Component()])
let result = Result(data: [someData])
//problem begins here
let pkCompent = result.data
var chatMsgs = result.data
print(pkCompent[0].components.count)
chatMsgs[0].components.removeAll()
print(pkCompent[0].components.count)
Inorder to avoid the reference issue, convert SomeData to struct
struct SomeData {
var components: [Component]
init(components : [Component]) {
self.components = components
}
}

Answer 2

You have 2 suggestions.
1- Deep copy .
2- Use struct instead of class since its value type.
Incase of deep copy this is a simple example,
when you assign something to new instance use this way.
// Deep copy
var foo = Foo()
var otherFoo = Foo(foo)
rather than this.
var fee = foo // shallow copy still the same referance
Note: this is handled by swift you don't have to add any inits to the class.

Answer 3

component is what you are removing it from and not the Array to
be precise.
While arrays implementation in swift is using a Struct which is a
value type and not a Object type, what your array is holding, i.e
Object of Chatbot_V_1_DataModel might as well be a class thus, the
elements held in your array are references to object of type
Chatbot_V_1_DataModel.
the way you can work around this is by having Chatbot_V_1_DataModel
defined as a struct thus, a value type OR by making a deep copy of
you array and then using that copy in you closure as you modify it.
I am talking about something on these lines:
var copie = arr.map{$0.mutableCopy()}
better yet:
var PKComponents = [Chatbot_V_1_DataModel]()
var ChatMessages = [Chatbot_V_1_DataModel]()
override func viewDidLoad() {
super.viewDidLoad()
var copie = arr.map{$0.mutableCopy()} // use this copy now elsewhere!!!
GetChatBotData() {(result: ChatbotV_1_Model!) in
print("Call Plans: \(result!)")
self.PKComponents = result.data
self.ChatMessages = result.data
self.ChatMessages[0].component.removeAll()
}

Answer 4

This is the problem of deep copying. Either you write a complete initializer that copies everything and create a new object and use that instead of just assignment. Or use struct instead of class. But as a quick fix you can explicitly only copy the component array like this:
self.PKCOMPONENTS = results.data
self.PKCOMPONENTS.components = Array(results.data.components)