设置UIView图层的锚点

Question

我有一个UIView子类,我希望能够在它的superview中移动.当用户在外面某处触摸UIView self.center但在self.bounds其中"跳跃"时,因为我添加新位置self.center以实现实际移动.为了避免这种行为,我试图设置一个锚点,让用户抓住并拖动视图在其范围内的任何位置.

我的问题是,当我计算新的锚点(如下面的代码所示)没有任何反应时,视图根本不会改变位置.另一方面,如果我将锚点设置为预先计算的点,我可以移动视图(但当然它会"跳转"到预先计算的点).为什么这不能按预期工作？

谢谢.

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event 
{
    // Only support single touches, anyObject retrieves only one touch
    UITouch *touch = [touches anyObject];
    CGPoint locationInView = [touch locationInView:self];

    // New location is somewhere within the superview
    CGPoint locationInSuperview = [touch locationInView:self.superview];

    // Set an anchorpoint that acts as starting point for the move
    // Doesn't work!
    self.layer.anchorPoint = CGPointMake(locationInView.x / self.bounds.size.width, locationInView.y / self.bounds.size.height);
    // Does work!
    self.layer.anchorPoint = CGPointMake(0.01, 0.0181818);

    // Move to new location
    self.center = locationInSuperview;
}

Answer 1

正如Kris Van Bael指出的那样,你需要在touchsBegan:withEvent:方法中进行锚点计算,以免否定运动.此外,由于更改图层anchorPoint将移动视图的初始位置,因此您必须向视图的center点添加偏移以避免在第一次触摸后"跳转".

您可以通过根据center初始和最终anchorPoints之间的差异(乘以视图的宽度/高度)计算(并添加到视图的点)偏移量,或者可以将视图设置center为初始触摸点.

也许这样的东西:

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {

    UITouch *touch = [touches anyObject];
    CGPoint locationInView = [touch locationInView:self];
    CGPoint locationInSuperview = [touch locationInView:self.superview];

    self.layer.anchorPoint = CGPointMake(locationInView.x / self.frame.size.width, locationInView.y / self.frame.size.height);
    self.center = locationInSuperview;
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {

    UITouch *touch = [touches anyObject];
    CGPoint locationInSuperview = [touch locationInView:self.superview];

    self.center = locationInSuperview;
}

关于更多信息anchorPoint从苹果的文档的位置和相似,所以怀疑我引用在这里.