@Published property inside an NSManagedObject doesn't trigger view updates

Question

I have a Core Data data model that I use in my app, and would like to add a property to that data model that I don't necessarily want to store, so instead of @NSManaged I made that property @Published.

 @Published var currentTime = "00:00"

And in the view instances I, of course, use an @ObservedObject

 @ObservedObject var timeItem: TimeItem

And in that view, I use a timer to update that value

.onReceive(Timer.publish(every: 0.015, on: .main, in: .common).autoconnect()) { time in
     timeItem.currentTime = timeItem.timeFinished.timeIntervalSince(Date()).editableStringMilliseconds()
 }

However, that doesn't trigger the view updates. I'm not sure if NSManagedObject is to blame, but if I replace that timeItem.currentTime value with a local @State one, everything works.

@State private var currentTime: String = "00:00"

Any ideas fellas?

Does your Object implement ObservableObject ?

JIE WANG
– JIE WANG

2020-12-23 16:49:54 +00:00
Commented Dec 23, 2020 at 16:49 — JIE WANG
– JIE WANG, Commented Dec 23, 2020 at 16:49

Alexander · Accepted Answer · 2021-02-28 14:35:14Z

2

It's seems that there is a bug here or whatever it is. I had the same problem. To solve this issue you must trigger publisher manually:

 @Published var currentTime = "00:00" {
     willSet {
         objectWillChange.send()
     }
 }

At this moment you even don't need @Published wrapper.

To trigger update of @NSManaged properties you can override willChangeValue method.

override public func willChangeValue(forKey key: String) {  
    super.willChangeValue(forKey: key)  
    self.objectWillChange.send()  
}

I hope Apple will fix this strange behaviour as soon as possible.

answered Feb 28, 2021 at 14:35

Alexander

831 silver badge7 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Kaunteya Over a year ago

It is strongly discouraged to override willChangeValue method here. developer.apple.com/documentation/coredata/…

Collectives™ on Stack Overflow

@Published property inside an NSManagedObject doesn't trigger view updates

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related