Swift中的外观代理/ UI_APPEARANCE_SELECTOR？

苹果文档说明：

To participate in the appearance proxy API,tag your appearance
property selectors in your header with UI_APPEaraNCE_SELECTOR.

在Objective-C中，可以使用UI_APPEaraNCE_SELECTOR注释属性，如下所示：

@property (nonatomic,strong) UIColor *foregroundColor UI_APPEaraNCE_SELECTOR;

我怎么能在Swift中做同样的事情？

将自定义视图属性标记为动态。

例如：

class YourCustomView: UIView {
    dynamic var subviewColor: UIColor? {
        get { return self.yourSubview.backgroundColor }
        set { self.yourSubview.backgroundColor = newValue }
    }
    ...
}

然后：

YourCustomView.appearance().subviewColor = UIColor.greenColor()