New stored property always returns nil | iOS Swift

Question

A new stored property created for exisiting class using extension. While getting value its always returning nil value. The below code is what i tried to add new stored property.

var IdentifiableIdKey   = "kIdentifiableIdKey"
extension EKEvent {
    
    public var customId: Int {
        get {
            return (objc_getAssociatedObject(self, &IdentifiableIdKey) as? Int) ?? 0
        }
        set {
            print("\(newValue)")
            objc_setAssociatedObject(self, &IdentifiableIdKey, newValue, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
        }
    }
    
}

Utilisation

let eventStore = EKEventStore()
let calendars = eventStore.calendars(for: .event)

for calendar in calendars {
    
       if calendar.title == "Events" {
                                    
         let oneMonthAgo = NSDate(timeIntervalSinceNow: -30*24*3600)

         let oneMonthAfter = NSDate(timeIntervalSinceNow: +30*24*3600)
                            
         let predicate = eventStore.predicateForEvents(withStart: oneMonthAgo as Date, end: oneMonthAfter as Date, calendars: [calendar])
                            
         let events = eventStore.events(matching: predicate)
                                    
           for event in events {                                        
                print("evnet id \(event.customId)")

                }
             }
          }

Somebody help me to find the mistake I did. Thanks in advance.

How are you getting its value? Are you sure you are accessing the same `EKEvent`? — Sweeper, Sep 15 '20 at 07:02
I can do `let a = EKEvent(eventStore: EKEventStore());a.customId = 1;print(a.customId)` and it will print 1 as expected. What code did you use? — Sweeper, Sep 15 '20 at 07:04
I'm not familiar with EventKit enough to tell you whether that's possible or not. I've only used it once. But why do you need a `customId` when `EKEvent` already has `eventIdentifier`? — Sweeper, Sep 15 '20 at 07:19
[This](https://stackoverflow.com/questions/4440420/store-a-custom-value-in-a-ekevent-iphone-calendar) seems like a duplicate, but I'm not familiar with event kit enough to be sure... — Sweeper, Sep 15 '20 at 07:20
Well, it is a read-only property because it is set automatically by EventKit. You don't need to set it. You are not supposed to set the ID of an event. EventKit _is_. See the possible duplicate for more details. — Sweeper, Sep 15 '20 at 07:22

score 2 · Accepted Answer · answered Sep 15 '20 at 10:11

2

The fact is that objc_getAssociatedObject/objc_setAssociatedObject assign a value to an object instance so it can be alive with this instance only. Since your custom property is not serialised by EventKit it's naturally that new obtained instances of events after the request have no associated objects.

answered Sep 15 '20 at 10:11

iUrii

11,742
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so what is the solution? – Code cracker Sep 15 '20 at 10:15
You can look at this answer - https://stackoverflow.com/questions/32550287/how-to-add-some-additional-fields-to-ekevent. Or also you can try to make your second store e.g. dictionary that maps `eventIdentifier` to your custom data but in this way you should synchronise all changes each time programatically. – iUrii Sep 15 '20 at 10:27

score -2 · Answer 2 · answered Sep 15 '20 at 06:59

-2

Extensions in Swift can add computed instance properties and computed type properties only https://docs.swift.org/swift-book/LanguageGuide/Extensions.html

answered Sep 15 '20 at 06:59

Roman Ryzhiy

1,540
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He added a computed instance property. – gnasher729 Sep 15 '20 at 07:11

score -2 · Answer 3 · answered Sep 15 '20 at 07:13

-2

It's called objc_setAssociatedObject. See the "Object" at the end? An Int is not an object. Turn your newValue into an NSNumber so you have an object. So that is definitely not going to work.

If your class is not an @objc class that might be a problem.

answered Sep 15 '20 at 07:13

gnasher729

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An `Int` is *automatically* wrapped into an `NSNumber` when passed to an Objective-C function taking an object parameter. This *does* work. – Martin R Sep 15 '20 at 07:26
No luck with NSNumber :( – Code cracker Sep 15 '20 at 07:29

New stored property always returns nil | iOS Swift

3 Answers3