更改我的CALayer的anchorPoint会移动视图

Question

我想改变anchorPoint，但保持视图在同一个地方。我试过NSLog-ing分词self.layer.position和self.center他们都保持不变，无论更改anchorPoint的。然而我的观点却在变化关于如何做到这一点的任何提示？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);输出是：2009-12-27 20:43:24.161 Type[11289:207] center point: 272.500000 242.5000002009-12-27 20:43:24.162 Type[11289:207] center point: 272.500000 242.500000

Answer 1

Core Animation Programming Guide 的Layer Geometry and Transforms部分解释了CALayer的position和anchorPoint属性之间的关系。基本上，层的位置是根据图层的anchorPoint的位置指定的。默认情况下，图层的anchorPoint为（0.5,0.5），位于图层的中心。设置图层的位置时，您将在其超层图层的坐标系中设置图层中心的位置。

因为位置是相对于图层的anchorPoint，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考虑新的anchorPoint。我这样做的一种方法是抓取图层的边界，将边界的宽度和高度乘以旧的和新的anchorPoint的标准化值，取两个anchorPoints的差值，并将该差值应用于图层的位置。

您甚至可以通过使用CGPointApplyAffineTransform()UIView的CGAffineTransform以这种方式考虑轮换。

Answer 2

我有同样的问题。Brad Larson的解决方案即使在视图旋转时也能很好地工作。这是他的解决方案翻译成代码。

-(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;

}

而快速的等价物：

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

}