代码在playground中实现

//: Playground - noun: a place where people can playimport UIKitclass MyView : UIView{    override func drawRect(rect: CGRect) {        //获取绘制上下文        var context = UIGraphicsGetCurrentContext()                //计算要在其中绘制的矩形        var pathRect = CGRectInset(self.bounds, self.bounds.size.width*0.1, self.bounds.size.height*0.1)                //创建一个圆角矩形路径        var rectanglePath = UIBezierPath(roundedRect: pathRect, cornerRadius: 20)                //等价于保存上下文        CGContextSaveGState(context)                //准备阴影        var shadow = UIColor.blackColor().CGColor        var shadowOffset = CGSize(width: 3, height: 3)        var shadowBlurRadius : CGFloat = 5.0                //此函数创建和应用阴影        CGContextSetShadowWithColor(context, shadowOffset, shadowBlurRadius, shadow)                //绘制路径；它将带有一个阴影        UIColor.redColor().setFill()        rectanglePath.fill()                //等价于重载上下文        CGContextRestoreGState(context)    }}let viewRect = CGRect(x: 0, y: 0, width: 100, height: 100)let myEmptyView = MyView(frame:viewRect)myEmptyView.backgroundColor = UIColor.clearColor()

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