我正在尝试在用户选择一个切片时旋转饼图轮，并让该切片停在轮的顶部//startfromthemiddleofthesliceangleletstartAngle=self.slicesArray[index].angle/2//endattopofchartletendAngle=//?letangleDifference=//?UIView.animateWithDuration(0.4,animations:{self.transform=CGAffineTransformRotate(self.transform,-angleDifference)})