更改CALayer的anchorPoint会移动视图

Question

我想改变anchorPoint，但保持视图不变。我尝试过NSLog、-ing、self.layer.position和self.center，不管anchorPoint有什么变化，它们都保持不变。然而，我的观点却在移动！

关于如何做到这一点，有什么建议吗？

self.layer.anchorPoint = CGPointMake(0.5, 0.5);
NSLog(@"center point: %f %f", self.layer.position.x, self.layer.position.y);
self.layer.anchorPoint = CGPointMake(1, 1);
NSLog(@"center point: %f %f", self.layer.position.x, self.layer.position.y);

输出为：

2009-12-27 20:43:24.161 Type[11289:207] center point: 272.500000 242.500000
2009-12-27 20:43:24.162 Type[11289:207] center point: 272.500000 242.500000

Answer 1

核心动画编程指南的Layer Geometry and Transforms部分解释了CALayer的位置和anchorPoint属性之间的关系。基本上，层的位置是根据层的anchorPoint的位置指定的。默认情况下，层的anchorPoint为(0.5，0.5)，它位于层的中心。设置层的位置时，将设置层在其上层的坐标系中的中心位置。

因为该位置是相对于图层的anchorPoint的，所以在保持相同位置的同时更改该anchorPoint会移动图层。为了防止这种移动，您需要调整图层的位置以适应新的anchorPoint。我这样做的一种方法是抓取层的边界，将边界的宽度和高度乘以新旧锚点的归一化值，取两个anchorPoints的差值，并将该差值应用于层的位置。

您甚至可以通过将CGPointApplyAffineTransform()与您的‘s视图的CGAffineTransform一起使用来说明旋转。

Answer 2

我也有同样的问题。Brad Larson的解决方案即使在视图旋转时也能很好地工作。以下是他的解决方案转换为代码。

-(void)setAnchorPoint:(CGPoint)anchorPoint forView:(UIView *)view
{
    CGPoint newPoint = CGPointMake(view.bounds.size.width * anchorPoint.x, 
                                   view.bounds.size.height * anchorPoint.y);
    CGPoint oldPoint = CGPointMake(view.bounds.size.width * view.layer.anchorPoint.x, 
                                   view.bounds.size.height * view.layer.anchorPoint.y);

    newPoint = CGPointApplyAffineTransform(newPoint, view.transform);
    oldPoint = CGPointApplyAffineTransform(oldPoint, view.transform);

    CGPoint 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 = anchorPoint;
}

和迅捷的等价物：

func setAnchorPoint(anchorPoint: CGPoint, forView view: UIView) {
    var newPoint = CGPointMake(view.bounds.size.width * anchorPoint.x, view.bounds.size.height * anchorPoint.y)
    var oldPoint = CGPointMake(view.bounds.size.width * view.layer.anchorPoint.x, view.bounds.size.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 = anchorPoint
}

SWIFT 4.x

func setAnchorPoint(anchorPoint: CGPoint, forView view: UIView) {
    var newPoint = CGPoint(x: view.bounds.size.width * anchorPoint.x,
                           y: view.bounds.size.height * anchorPoint.y)


    var oldPoint = CGPoint(x: view.bounds.size.width * view.layer.anchorPoint.x,
                           y: view.bounds.size.height * view.layer.anchorPoint.y)

    newPoint = newPoint.applying(view.transform)
    oldPoint = oldPoint.applying(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 = anchorPoint
}

Answer 3

解决这个问题的关键是使用frame属性，奇怪的是，它是唯一改变的东西。

Swift 2

let oldFrame = self.frame
self.layer.anchorPoint = CGPointMake(1, 1)
self.frame = oldFrame

Swift 3

let oldFrame = self.frame
self.layer.anchorPoint = CGPoint(x: 1, y: 1)
self.frame = oldFrame

然后我调整大小，它从anchorPoint缩放。然后我必须恢复旧的anchorPoint；

Swift 2

let oldFrame = self.frame
self.layer.anchorPoint = CGPointMake(0.5,0.5)
self.frame = oldFrame

Swift 3

let oldFrame = self.frame
self.layer.anchorPoint = CGPoint(x: 0.5, y: 0.5)
self.frame = oldFrame

编辑:如果旋转视图，则此选项会消失，因为如果应用了CGAffineTransform，则frame属性是未定义的。