在iOS上绘制阴影

//: Playground - noun: a place where people can play

import UIKit

class 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()