IOS UIResponder 触碰拖动图像

override func touchesMoved(_ touches：Set, with event：UIEvent？) {
//需要先判断是否触屏区域是否在图像内，省略
if！isTouchInImageView{
return;
}
let touch = touches.first
let touchPoint = touch？.location(in：self.view)
let touchPrePoint = touch？.previousLocation(in：self.view)
let disX = (touchPoint？.x)！- (touchPrePoint？.x)！
let disY = (touchPoint？.y)！- (touchPrePoint？.y)！
var centerPoint = self.imageView.center
centerPoint.x += disX
centerPoint.y += disY
self.imageView.center = centerPoint
}