随机背景颜色

        /// 获取随机颜色
        let color = UIColor(red: CGFloat(randomIn(0, max: 255))/255.0, green: CGFloat(randomIn(0, max: 255))/255.0, blue: CGFloat(randomIn(0, max: 255))/255.0, alpha: 1.0)

        
        self.view.backgroundColor = color
        
        //定义渐变的颜色，多色渐变太魔性了，我们就用两种颜色
        let topColor = UIColor(red: (CGFloat(randomIn(50, max: 205))/255.0), green: (CGFloat(randomIn(50, max: 205))/255.0), blue: (CGFloat(randomIn(50, max: 205))/255.0), alpha: 1)

        //将颜色和颜色的位置定义在数组内
        let gradientColors: [CGColor] = [topColor.CGColor, color.CGColor]
        let gradientLocations: [CGFloat] = [0.0, 1.0]
        
        //创建CAGradientLayer实例并设置参数
        let gradientLayer: CAGradientLayer = CAGradientLayer()
        gradientLayer.colors = gradientColors
        gradientLayer.locations = gradientLocations
        
        //设置其frame以及插入view的layer
        gradientLayer.frame = self.view.frame
        self.view.layer.insertSublayer(gradientLayer, atIndex: 0)

    /**
     获取随机函数
     
     - parameter min: 最小值
     - parameter max: 最大值
     
     - returns: 返回随机数
     */
    func randomIn(min: Int, max: Int) -> Int {
        return Int(arc4random()) % (max - min + 1) + min
    }