生成线的代码：
self.path = [UIBezierPath bezierPath];

[self.path moveToPoint:from]; [self.path addLineToPoint:to]; self.pathLayer = [CAShapeLayer layer]; self.pathLayer.frame = containerView.bounds; self.pathLayer.path = self.path.CGPath; self.pathLayer.strokeColor = color.CGColor; self.pathLayer.lineWidth = 2.0f; self.pathLayer.lineJoin = kCALineJoinBevel; NSMutableArray *ary = [NSMutableArray arrayWithArray:shapeLayers]; [ary addObject:self.pathLayer]; shapeLayers = [NSMutableArray arrayWithArray:ary]; [containerView.layer addSublayer:self.pathLayer];

如何将上述线删除，在画新线