Swift 3.0 CAlayer画渐变色

letstressLayer:CAShapeLayer=CAShapeLayer()

stressLayer.frame= .init(x:0,y: Avglabel.frame.maxY,width:SCREEN_WIDTH,height:40)

gradientLater:CAGradientLayer=CAGradientLayer()

gradientLater.frame= stressLayer.bounds

gradientLater.colors= [stress_greenColor.cgColor,

stress_blueColor.stress_orangeColor.stress_redColor.cgColor]

gradientLater.locations= [ 0.25,216);">0.5,216);">0.75,216);">1.0];

gradientLater.startPoint=CGPoint.0.5)

gradientLater.endPoint=1,216);">0.5)

stressLayer.addSublayer(gradientLater)