Parent variable is not updated for the ChildViewController - ios

Question

I have a class which is inherited from BaseViewController.swift. I have defined a flag for core data changes tracking:
var coreDataUpdated: Bool?
I've also added an observer for core data changes in viewWillAppear of BaseViewController.swift
//Core data update
NotificationCenter.default.addObserver(self,
selector: #selector(self.CoreDataUpadated),
name: .NSManagedObjectContextObjectsDidChange,
object: nil)
Now whenever I notified about changes in core data, I change coreDataUpdated variable to true
#objc func CoreDataUpadated() {
self.coreDataUpdated = true
}
Now in my ChildViewController.swift in viewDidAppear when I check for coreDataUpdated it returns me nil
here is my complete code:
class BaseViewController: UIViewController {
var coreDataUpdated: Bool?
override func viewWillAppear(_ animated: Bool) {
//Core data update
NotificationCenter.default.addObserver(self,
selector: #selector(self.CoreDataUpadated),
name: .NSManagedObjectContextObjectsDidChange,
object: nil)
}
func CoreDataUpadated() {
self.coreDataUpdated = true
}
}
class ChildViewController: BaseViewController {
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
reloadData()
}
func reloadData() {
if super.coreDataUpdated ?? false { //I always get nil for
super.coreDataUpdated
tableView?.reloadData()
}
}
}
Notice: I'm working on Xcode 9 beta 5 and iOS 11 with swift 4. However this code works fine on the Xcode 8 and iOS 10.3 with swift 3.

Answer 1

Class inheritance does not mean that subclass instances inherit the values assigned to properties in superclass instances.
You have an instance of BaseViewController which has a coreDataUpdated property and instance of ChildViewController, which has a coreDataUpdated property since it inherits from BaseViewController, but it's property value is unrelated to the BaseViewController instance property value; they are different objects.
When you say self.coreDataUpdated = true you are setting the property on the BaseViewController instance.
When you say super.coreDataUpdated you are referring to the coreDataUpdated property in the ChildViewController instance that is defined by it's superclass; since this property has never been assigned a value it is nil.
Since ChildViewController does not override coreDataUpdated super.coreDataUpdated is the same as self.coreDataUpdated in an instance of ChildViewController, so you could re-write that if statement as:
func reloadData() {
if self.coreDataUpdated ?? false {
tableView?.reloadData()
}
}
Hopefully this makes it clearer as to why coreDataUpdated is nil
Rather than using your own Bool, it may be simpler to examine the hasChanges property of your NSManagedObjectContext instance.

Answer 2

Thanks to #Paulw11 comments, I found out with inheritance the value won't be shared. So I use KVC pattern as the solution. this is my code after change
enum coreDataState: String {
case inserted = "inserted"
case deleted = "deleted"
case updated = "updated"
var description: String {
switch self {
case .inserted: return "inserted"
case .deleted: return "deleted"
case .updated: return "updated"
}
}
}
class BaseViewController: UIViewController {
override func viewWillAppear(_ animated: Bool) {
//Core data update
NotificationCenter.default.addObserver(self,
selector: #selector(self.CoreDataUpadated),
name: .NSManagedObjectContextObjectsDidChange,
object: nil)
}
func CoreDataUpdated(_ notification: Notification) {
if let userDictionary = notification.userInfo as? Dictionary<String, Any> {
for KV in userDictionary {
if KV.key != "managedObjectContext" {
NSUserDefaultManager.SaveItem(KV.key, key: coreDataUpdateKey)
}
}
}
}
func CoreDataChanged() -> coreDataState? {
if let currentState = NSUserDefaultManager.LoadItem(coreDataUpdateKey) as? String {
NSUserDefaultManager.RemoveItem(coreDataUpdateKey)
return coreDataState(rawValue: currentState)
}
return nil
}
}
class ChildViewController: BaseViewController {
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
reloadData()
}
func reloadData() {
if super.CoreDataChanged() != .deleted {
loadData()
tableView?.reloadData()
}
}
}
Although it is possible to implement it with other patterns such as delegate or override the CoreDataUpdated function in child classes