我的问题是关于是否可以在Swift上的Singleton属性上使用KVC。我在课堂上测试KVC可以使它起作用,但决定查看它是否在Singleton课程上起作用。
我遇到了一个错误,说明我的单例的"共享"属性不符合KVC。
class KVOObject: NSObject {
@objc static let shared = KVOObject()
private override init(){}
@objc dynamic var fontSize = 18
}
override func viewDidLoad() {
super.viewDidLoad()
addObserver(self, forKeyPath: #keyPath(KVOObject.shared.fontSize), options: [.old, .new], context: nil)
}
override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
if keyPath == #keyPath(KVOObject.shared.fontSize) {
// do something
}
}
我目前正在遇到以下错误:
NetworkCollectionTest [9714:452848] ***由于未知的例外'NSunknowneKeyException'终止应用程序'不适合"共享"属性的KVC。'
关键路径不正确。是KVOObject.fontSize
。而且您需要将观察者添加到那个单身人士:
KVOObject.shared.addObserver(self, forKeyPath: #keyPath(KVOObject.fontSize), options: [.old, .new], context: nil)
顺便说一句,(a)您可能应该使用上下文来确定您是否正在处理此问题,或者超级类是否可以使用它;(b)如果不是您的,则应致电super
实现;(c)确保在deinit
上删除观察者:
class ViewController: UICollectionViewController {
private var observerContext = 0
override func viewDidLoad() {
super.viewDidLoad()
KVOObject.shared.addObserver(self, forKeyPath: #keyPath(KVOObject.fontSize), options: [.new, .old], context: &observerContext)
}
override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
if context == &observerContext {
// do something
} else {
super.observeValue(forKeyPath: keyPath, of: object, change: change, context: context)
}
}
deinit {
KVOObject.shared.removeObserver(self, forKeyPath: #keyPath(KVOObject.fontSize))
}
...
}
或者,如果在Swift 4中,它现在要容易得多,因为它是基于封闭的(避免需要上下文),并且当NSKeyValueObservation
脱离范围时会自动删除:
class ViewController: UICollectionViewController {
private var token: NSKeyValueObservation?
override func viewDidLoad() {
super.viewDidLoad()
token = KVOObject.shared.observe(.fontSize, options: [.new, .old]) { [weak self] object, change in
// do something
}
}
...
}
顺便说一句,对单人的一些观察:
shared
属性不需要@objc
预选赛;只有被观察到的财产需要;和init
方法确实应该调用super
;和我可能还将其声明为
final
因此:
final class KVOObject: NSObject {
static let shared = KVOObject()
override private init() { super.init() }
@objc dynamic var fontSize: Int = 18
}