我想创建一个渐变的圆形路径，如下图所示:我有以下代码:circularPath=UIBezierPath(arcCenter:.zero,radius:radius,startAngle:0,endAngle:.pi*2,clockwise:true)outerTrackShapeLayer=CAShapeLayer()outerTrackShapeLayer.path=circularPath.cgPathouterTrackShapeLayer.position=positionouterTrackShapeLayer.strokeColor=outerTrackColor.cgC