Mac鼠标样式设置

在开发Mac App 时，经常需要变换鼠标样式。实现鼠标样式的变换需要用到两个类：NSCursor、NSTrackingArea

下面一个最常用的业务场景：鼠标移到一串文字上时，鼠标变成小手指

首先需要定义一个追踪区域：

let area = NSTrackingArea.init(rect: bounds, options: [.activeAlways,.mouseEnteredAndExited], owner: self, userInfo: nil)
self.addTrackingArea(area)

接下来，需要实现追踪的方法：

    override func mouseExited(with event: NSEvent) {
        super.mouseExited(with: event)
        NSCursor.arrow.set()
    }
    
    override func mouseEntered(with event: NSEvent) {
        super.mouseEntered(with: event)
        NSCursor.pointingHand.set()
    }

其中NSCursor.arrow.set()及NSCursor.pointingHand.set()分别将鼠标设置为箭头和小手指。
可以很清楚的看出：当鼠标移入时，设为小手指；鼠标移出时，设为箭头。

demo:https://gitee.com/pengzhiyao/tutoral.git

参照：
https://stackoverflow.com/questions/32447739/changing-nscursor-for-nsview-above-an-nstextview
https://developer.apple.com/documentation/appkit/nscursor?language=objc