UserDefaultsObserver.swift

import Foundation

public final class UserDefaultsObserver: NSObject {
    public var onChange: (() -> Void)?
    private weak var object: NSObject?
    private let keyPaths: [String]

    public init(
        object: NSObject,
        forKeyPaths keyPaths: [String],
        context: UnsafeMutableRawPointer?
    ) {
        self.object = object
        self.keyPaths = keyPaths
        super.init()
        for keyPath in keyPaths {
            object.addObserver(self, forKeyPath: keyPath, options: .new, context: context)
        }
    }

    deinit {
        for keyPath in keyPaths {
            object?.removeObserver(self, forKeyPath: keyPath)
        }
    }

    public override func observeValue(
        forKeyPath keyPath: String?,
        of object: Any?,
        change: [NSKeyValueChangeKey: Any]?,
        context: UnsafeMutableRawPointer?
    ) {
        onChange?()
    }
}