UIViewPropertyAnimator问题与Autolayout

Question

这里是我试图重复的代码，根据Apple WWDC，但使用自动收费：

    extension AugmentedReallityViewController {
    @objc func handlePan(recognizer: UIPanGestureRecognizer) {
//        // hide languages and units anyway
//        moveUnitView(show: false)
//        moveLanguageView(show: false)
//
//        let isNowExpanded = settingsPanelState == SettingsPanelState.expanded
//        let newState = isNowExpanded ? SettingsPanelState.collapsed : SettingsPanelState.expanded
//
//        switch recognizer.state {
//        case .began:
//            startInteractiveTransition(state: newState, duration: 1)
//            isLastPanelUpdateToReachTheNewState = true // just in case, but we should change this property later
//        case .changed:
//            let translation = recognizer.translation(in: viewSettings)
//            let fractionComplete = translation.y / viewSettings.frame.size.height
//
//            // we will use this property when interaction ends
//            if fractionComplete != 0 { // if it's == 0 , we need to use prev data
//                isLastPanelUpdateToReachTheNewState = (newState == SettingsPanelState.expanded && fractionComplete < 0) || (newState == SettingsPanelState.collapsed && fractionComplete > 0)
//            }
//
//            updateInteractiveTransition(fractionComplete: fractionComplete)
//        case .ended:
//            continueInteractiveTransition(cancel: !isLastPanelUpdateToReachTheNewState)
//        default:
//            break
//        }
    }

    @objc func handleSettingsTap() {
        // hide languages and units anyway
        moveUnitView(show: false)
        moveLanguageView(show: false)

        let isNowExpanded = settingsPanelState == SettingsPanelState.expanded
        let newState = isNowExpanded ? SettingsPanelState.collapsed : SettingsPanelState.expanded

        animateOrReverseRunningTransition(state: newState, duration: 10)
    }

    // perform all animations with animators if not already running
    private func animateTransitionIfNeeded(state: SettingsPanelState, duration: TimeInterval) {

        if runningAnimators.isEmpty {

//            // define constraint for frame animation
//            // update constraints
//            switch state {
//            case .expanded:
//                constraint_settingsView_bottom.constant = 0
//            case .collapsed:
//                constraint_settingsView_bottom.constant = -constraint_height_settingViewWhitePart.constant
//            }
            // animate that
            let frameAnimator = UIViewPropertyAnimator(duration: duration, curve: .linear, animations: { [weak self] in
                if let strongSelf = self {
                    // define constraint for frame animation
                    // update constraints
                    switch state {
                    case .expanded:
                        strongSelf.constraint_settingsView_bottom.constant = 0
                    case .collapsed:
                        strongSelf.constraint_settingsView_bottom.constant = -(strongSelf.constraint_height_settingViewWhitePart.constant)
                    }
                }

                self?.view.layoutIfNeeded()
            })
            frameAnimator.startAnimation()
            runningAnimators.append(frameAnimator)
            frameAnimator.addCompletion({ [weak self] (position) in
                if position == UIViewAnimatingPosition.end { // need to remove this animator from array
                    if let index = self?.runningAnimators.index(of: frameAnimator) {
                        print("removed animator because of completion")
                        self?.runningAnimators.remove(at: index)
                        // we can change state to a new one
                        self?.settingsPanelState = state
                    }
                    else {
                        print("animator completion with state = \(position)")
                    }
                }
            })
        }
    }

    // starts transition if neccessary or reverses it on tap
    private func animateOrReverseRunningTransition(state: SettingsPanelState, duration: TimeInterval) {
        if runningAnimators.isEmpty { // start transition from start to end
            animateTransitionIfNeeded(state: state, duration: duration)
        }
        else { // reverse all animators
            for animator in runningAnimators {
                animator.stopAnimation(true)
                animator.isReversed = !animator.isReversed
                // test
                print("tried to reverse")
            }
        }
    }

    // called only on pan .begin
    // starts transition if neccessary and pauses (on pan .begin)
    private func startInteractiveTransition(state: SettingsPanelState, duration: TimeInterval) {
        animateTransitionIfNeeded(state: state, duration: duration)
        for animator in runningAnimators {
            animator.pauseAnimation()

            // save progress of any item
            progressWhenInterrupted = animator.fractionComplete
        }
    }

    // scrubs transition on pan .changed
    private func updateInteractiveTransition(fractionComplete: CGFloat) {
        for animator in runningAnimators {
            animator.fractionComplete = fractionComplete + progressWhenInterrupted
        }
    }

    // continue or reverse transition on pan .ended
    private func continueInteractiveTransition(cancel: Bool) {
        for animator in runningAnimators {
            // need to continue or reverse
            if !cancel {
                let timing = UICubicTimingParameters(animationCurve: .easeOut)
                animator.continueAnimation(withTimingParameters: timing, durationFactor: 0)
            }
            else {
                animator.isReversed = true
            }
        }
    }

    private func addPanGustureRecognizerToSettings() {
        let panGestureRecognizer = UIPanGestureRecognizer(target: self, action: #selector(AugmentedReallityViewController.handlePan(recognizer:)))
//        panGestureRecognizer.cancelsTouchesInView = false
        viewSettings.addGestureRecognizer(panGestureRecognizer)
    }

    private func addTapGestureRecognizerToSettings() {
        let tapGestureRecognizer = UITapGestureRecognizer(target: self, action: #selector(AugmentedReallityViewController.handleSettingsTap))
        tapGestureRecognizer.cancelsTouchesInView = false
        viewSettingsTopTriangle.addGestureRecognizer(tapGestureRecognizer)
    }
}

现在我只是在测试踢踏舞姿势。有两个主要问题：

1) Tap识别器在动画过程中不能正常工作。但是在苹果WWDC中，他们改变了帧(而不是像我这样的约束)，并且点击识别器工作得很好。

2)如果我改变了反向属性，那么约束就会改变得非常糟糕。我有多余的条子等等

( 3)在动画块和动画内部都尝试了改变约束的方法。这真的不重要，工作一样

，有什么帮助，如何用自动收费？或者至少如何使用框架，但是我的视图控制器是基于自动收费的，所以无论如何，我对这个底层视图都有限制。

Answer 1

当您在动画中使用autolayout时，如下所示：

1. 确保自动收费表已完成： self.view.layoutIfNeeded()
2. 然后更改动画块之前的约束。例如： someConstraint.constant =0
3. 然后，在更改约束后，告诉自动收费输出约束已经更改： self.view.setNeedsLayout()
4. 然后添加一个动画块，只需调用layoutIfNeeded()： UIView.animate(withDuration: 1，动画：{ self.view.layoutIfNeeded() })

在使用UIViewPropertyAnimator时也是如此--更改动画块中的约束。例如：

self.view.layoutIfNeeded()
someConstraint.constant = 0
self.view.setNeedsLayout()
let animator = UIViewPropertyAnimator(duration: 1, curve: .easeInOut) {            
    self.view.layoutIfNeeded()
}
animator.startAnimation()

这是因为layoutIfNeeded()执行实际的布局-它计算受影响视图的帧。因此，如果直接设置框架，则在动画块中设置它们。但是，Autolayout为您设置框架-因此，您需要的是告诉autolayout在动画块中设置它们(就像您要做的那样，如果您要直接设置它们)。layoutIfNeeded()调用正是这样做的-它告诉自动收费引擎计算和设置新的帧。

关于反转的：

虽然我没有足够的经验来100%确定，但我希望简单地设置动画师逆转是不够的。因为您在启动动画之前应用了这些约束，然后告诉autolayout根据这些约束更新框架--我假设当您反转动画器时，还需要反转驱动动画的约束。

动画师只是将视图动画到新的框架中。但是，无论反转与否，新的约束仍然有效，不管您是否反转了动画师。因此，在动画师完成之后，如果以后自动输出再次显示视图，我将期望视图进入当前活动约束设置的位置。简单地说：动画师动画帧的变化，但不是约束自己。这意味着逆转动画师反转帧，但它不会逆转约束--一旦自动输出完成另一个布局周期，它们将再次被应用。

Answer 2

设置self.view.layoutIfNeeded()动画发生的重要事项

private func animateCard(with topOffset: CGFloat) {
        let animator = UIViewPropertyAnimator(duration: 1, curve: .easeOut)

        animator.addAnimations {
            self.topCardConstraint?.constant = topOffset
            self.view.layoutIfNeeded()
        }

        animator.startAnimation()
    }