绘制渐变色背景

为满足设计需求，按钮背景颜色为渐变色，iOS 提供了CAGradientLayer 类来进行渐变色的设计

//layer进行渐变色设置
    func nextBtnCagradientLayer() {
        let btnLayer = CAGradientLayer.drawNextBtnGraduateColor(fromColor: "F73E46", toColor: "FBB13E")
        btnLayer.frame = nextBtnEnabel.bounds
        nextBtnEnabel.layer.insertSublayer(cagradientLayer,at: 1)
    }
class func drawNextBtnGraduateColor(fromColor:String,toColor:String)->CAGradientLayer{
        let gradentLayer = CAGradientLayer()
        //创建渐变色数组，转换为CGColor
        gradentLayer.colors = [UIColor.hexStringToColor(hexString:fromColor).cgColor,UIColor.hexStringToColor(hexString: toColor).cgColor]
        gradentLayer.startPoint = CGPoint.init(x: 0, y: 0)
        gradentLayer.endPoint = CGPoint.init(x: 1, y: 0)
        //设置颜色变化点,取值范围 0.0～1.0
        gradentLayer.locations = [0,1]
        return gradentLayer
}

注意:使用SnpKit约束控件进行渐变色设置无效，设置控件的frame才能绘制出渐变色