MacOS开发笔记-NSTrackingArea

区域跟踪有一个注意点，示例代码如下：

let track : NSTrackingArea = NSTrackingArea.init(rect: self.middleView.leftView.bounds, options: [.mouseMoved,.activeAlways,.inVisibleRect], owner: self, userInfo: nil)
       self.middleView.leftView.addTrackingArea(track)

其中options需要有这个三个参数，eg：[.mouseMoved,.activeAlways,.inVisibleRect]
三个参数必需取之于[mouseEnteredAndExited、mouseMoved、cursorUpdate]、[activeWhenFirstResponder、activeInKeyWindow、activeInActiveApp、activeAlways]和[assumeInside、inVisibleRect、enabledDuringMouseDrag]