修改layer的anchorPoint需要注意的问题

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    当我们需要做旋转动画时，默认情况都是以视图的中点作为轴进行旋转的，但有时我们需要改变旋转的轴，这个时候需要通过改变视图layer的anchorPoint属性来满足需求。

    anchorPoint是一个CGPoint类型，取值范围为(0, 0)~(1, 1)，默认值为(0.5, 0.5)。但直接改变anchorPoint会意外的发现视图的位置改变了。看下面这个例子：

self.aView = UIView(frame: CGRect(x: 0, y: 0, width: 120, height: 120))
self.aView.backgroundColor = UIColor.blackColor()
self.view.addSubview(aView)

println("view‘s bounds: \(self.aView.bounds)")
println("view‘s frame: \(self.aView.frame)")
println("view‘s center: \(self.aView.center)")

println("layer‘s bounds: \(self.aView.layer.bounds)")
println("layer‘s frame: \(self.aView.layer.frame)")
println("layer‘s position: \(self.aView.layer.position)")
println("layer‘s anchorPoint: \(self.aView.layer.anchorPoint)")

self.aView.layer.anchorPoint = CGPoint(x: 0, y: 0)

println()
println("view‘s bounds: \(self.aView.bounds)")
println("view‘s frame: \(self.aView.frame)")
println("view‘s center: \(self.aView.center)")

println("layer‘s bounds: \(self.aView.layer.bounds)")
println("layer‘s frame: \(self.aView.layer.frame)")
println("layer‘s position: \(self.aView.layer.position)")
println("layer‘s anchorPoint: \(self.aView.layer.anchorPoint)")

为了解决这个问题有两种方法：

1. 定义一个私有方法传入改变后的anchorPoint，和需要改变anchorPoint的view

private func setAnchorPoint(anchoPoint: CGPoint, forView view: UIView) {
    var newPoint: CGPoint = CGPoint(x: view.bounds.width * anchoPoint.x, y: view.bounds.height * anchoPoint.y)
    var oldPoint: CGPoint = CGPoint(x: view.bounds.width * view.layer.anchorPoint.y, y: view.bounds.height * view.layer.anchorPoint.y)
    
    newPoint = CGPointApplyAffineTransform(newPoint, view.transform)
    oldPoint = CGPointApplyAffineTransform(oldPoint, view.transform)
    
    var position = view.layer.position
    position.x -= oldPoint.x
    position.x += newPoint.x
    
    position.y -= oldPoint.y
    position.y += newPoint.y
    
    view.layer.position = position
    view.layer.anchorPoint = anchoPoint
}

var originRect = self.aView.frame
self.aView.layer.anchorPoint = CGPoint(x: 0, y: 0)
self.aView.frame = originRect

经过测试，两种方式的结果是相同的。

修改layer的anchorPoint需要注意的问题

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原文地址：http://my.oschina.net/u/1032381/blog/483901