Trying to replace old fashioned objective-c way of observation to modern swift way of observation. However I cannot figure out the keypath.

//doesn't work
progress.observe(.userInfo[ProgressUserInfoKey.fileCompletedCountKey], changeHandler: {_,_ in
        
})

PS: You cannot observe fileCompletedCount because is a computed property.

Old code:

import Cocoa
private var viewControllerObservationContext = 0

class ViewController: NSViewController {

    private var progress: Progress = {
        let progress = Progress()
        progress.kind = .file
        progress.fileTotalCount = 20
        return progress
    }()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        let filesCompletedKeyPath = "userInfo.NSProgressFileCompletedCountKey"
        progress.addObserver(self, forKeyPath: filesCompletedKeyPath, options: .new, context: &viewControllerObservationContext)
        DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
            self.progress.fileCompletedCount = 10
        }
    }

    override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey: Any]?, context: UnsafeMutableRawPointer?) {
        guard context == &viewControllerObservationContext else {
            super.observeValue(forKeyPath: keyPath, of: object, change: change, context: context)
            return
        }
        print(object)
        print(keyPath)
    }
}