ios - 使用 POPDecayAnimation 时动画不工作

Question

我为改变 View 制作下拉动画。当我使用 POPSpringAnimation 时，一切正常。但是当我将 POPSpringAnimation 更改为 POPDecayAnimation 时，什么也没有发生，在调试输出中我看到了这条消息:

ignoring to value on decay animation <POPDecayAnimation:0x7f9f2b5c8700; from = null; to = null; deceleration = 0.998000>

代码:

func switchViewController(from: UIViewController?, toViewController to: UIViewController?, animated: Bool) {

    if animated {
        to!.view.frame = self.view.frame
        // Not working when call trulySwitchViewController
        self.addChildViewController(to!)
        self.view.insertSubview(to!.view, belowSubview: from!.view)
        to!.didMoveToParentViewController(self)
        // Calculate new x coord
        var frame = from!.view.frame
        frame.origin.y += frame.size.height

        // POPDecayAnimation not working here
        var animation = POPDecayAnimation()
        animation.property = POPAnimatableProperty.propertyWithName(kPOPViewFrame) as POPAnimatableProperty
        animation.toValue = NSValue(CGRect:frame)
        animation.completionBlock = {
            (_, _) in
            self.trulySwitchViewController(from, toViewController: nil)
        }

        from!.view.pop_addAnimation(animation, forKey: "dropDown")
    } else {
        to?.view.frame = self.view.frame
        self.trulySwitchViewController(from, toViewController: to)
    }
}

Answer 1

对于衰减动画，您需要设置 velocity 属性，然后根据 deceleration 属性衰减到零。因此，不需要 to 属性，结束状态是根据起始位置、速度和减速度确定的。

您还需要为图层位置而不是 View 框架设置动画。所以像这样的东西应该工作......

var animation = POPDecayAnimation()
animation.property = POPAnimatableProperty.propertyWithName(kPOPLayerPosition) as POPAnimatableProperty

from!.view.layer.pop_addAnimation(animation, forKey: "dropDown")