ios开发之Swift在UIView上绘制图形阴影

import UIKit
 
class ViewController: UIViewController {
 
    override func viewDidLoad() {
        super.viewDidLoad()
         
        let viewRect = CGRect(x: 50, y: 50, width: 100, height: 100)
        let view1 = MyCanvas(frame: viewRect)
        self.view.addSubview(view1)
    }
 
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }
}
 
class MyCanvas: UIView {
    override init(frame: CGRect) {
        super.init(frame: frame)
        //把背景色设为透明
        self.backgroundColor = UIColor.clearColor()
    }
 
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
     
    override func drawRect(rect: CGRect) {
        //获取绘制上下文
        let context = UIGraphicsGetCurrentContext()
         
        //计算要在其中绘制的矩形
        let 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
        let rectanglePath = UIBezierPath(roundedRect: pathRect, cornerRadius: 20)
         
        //保存绘制设置
        CGContextSaveGState(context)
         
        //准备阴影
        let shadowColor = UIColor.blackColor().CGColor
        let shadowOffet = CGSize(width: 3, height: 3)
        let shadowBlurRadius:CGFloat = 5.0
         
        //创建和应用阴影
        CGContextSetShadowWithColor(context, shadowOffet, shadowBlurRadius, shadowColor)
         
        //绘制带有阴影的路径
        UIColor.blueColor().setFill()
        rectanglePath.fill()
         
        //还原绘制设置
        CGContextRestoreGState(context)
         
        //绘制另一个矩形（不带阴影）
        let pathRect2 = CGRectInset(self.bounds,
            self.bounds.size.width * 0.3,
            self.bounds.size.height * 0.3)
        let rectanglePath2 = UIBezierPath(rect: pathRect2)
        UIColor.yellowColor().setFill()
        rectanglePath2.fill()
    }
}