ios - Swift:在 init/deinit 中添加/删除观察者会在 Interface Builder 中引发错误

Question

我有一个可检查的简单 swift UI 组件 ( https://github.com/mbigatti/BMXCircularButton )。在 init/deinit 方法中，我调用了启动和停止对突出显示状态的观察。

init(frame: CGRect) {
    super.init(frame: frame)
    self.addObserver(self, forKeyPath: "highlighted", options: .New, context: nil)
}

init(coder aDecoder: NSCoder!) {
    super.init(coder: aDecoder)
    self.addObserver(self, forKeyPath: "highlighted", options: .New, context: nil)
}

deinit {
    self.removeObserver(self, forKeyPath: "highlighted")
}

这样做会导致 Interface Builder 出现以下错误:

file:///Users/max/Progetti/StatusApp/CircularButton/CircularButton/View.xib: error: 
Live Views: Failed to update auto layout status: Interface Builder Cocoa Touch Tool raised a "NSRangeException" 
exception: Cannot remove an observer <_TtC17BMXCircularButton14CircularButton 0x10ba98e00> 
for the key path "highlighted" from <_TtC17BMXCircularButton14CircularButton 0x10ba98e00> because it is not registered as an observer.

file:///Users/max/Progetti/StatusApp/CircularButton/CircularButton/View.xib: error: 
Live Views: Failed to render instance of _TtC17BMXCircularButton14CircularButton: Interface Builder Cocoa Touch Tool raised a "NSRangeException" 
exception: Cannot remove an observer <_TtC17BMXCircularButton14CircularButton 0x10bd055d0> 
for the key path "highlighted" from <_TtC17BMXCircularButton14CircularButton 0x10bd055d0> because it is not registered as an observer.

这可能是一个错误或我遗漏了什么？

Answer 1

正如 Kevin 所指出的，这里最好的答案实际上是在您的类重写中使用 didSet 和/或 willSet，因为您正在向 self 添加一个观察者。

override var highlighted:Bool {
    didSet {
        // Put your observerValue like code here
    }
}