新的API优点: Fluid, Responsive, Natural, Smooth

• Timing Functions
  UIView.animate(withDuration:2.0, delay: 0.0,
  options:[.linear]) {
  circle.center.x = 800.0
  }

  
  
  linear.png
  
  
  curve.png

• UIViewPropertyAnimator

  
  
  relationship.png

  let timing   = UICubicTimingParameters(animationCurve: .easeInOut)
  let animator = UIViewPropertyAnimator(duration: 2.0, timingParameters:timing)
  animator.addAnimations {
   // frame, center, alpha, and transform
  self.squareView.center = CGPoint(x: 800.0, y: self.squareView.center,y)
  self.squareView.transform = CGAffineTransform(rotationAngle: CGFloat(M_PI_2))
  }
    animator.addCompletion {_ in
    self.squareView.backgroundColor = UIColor.orange()
  }
  animator.startAnimation()
  

• 标准初始化后

startAnimation()

• 立即开始动画（类方法）

runningPropertyAnimator(withDuration:delay:options:animations:completion:)

• State

  
  
  State transitions for an animator object.png

var state: UIViewAnimatingState { get }
var isRunning: Bool { get }
var isReversed: Bool { get set }

• 动态修改动画

• Start, pause, resume, and stop animations

• Add animation blocks
  addAnimations(:) and addAnimations(:delayFactor:)

• Scrub through a paused animation by modifying the fractionComplete property.

• Change the animation’s direction using the isReversed property.

• Modify the timing and duration of a partially complete animation by pausing the animation and using the continueAnimation(withTimingParameters:durationFactor:) method to finish it.

UIViewAnimating

• Every newly created animator starts off in the inactive state. Similarly, an animator that has finished its animations returns to the inactive state.

• pauseAnimation() method :paused so that you can modify those animations.

• stopAnimation(_:) method: the animator object moves to the stopped or inactive state and must be reconfigured before it can be used again.

Timing providers

A cubic Bézier timing curve.png

// 1
UICubicTimingParameters()

UICubicTimingParameters(animationCurve: .linear)

UICubicTimingParameters(controlPoint1: CGPoint(x:0.0, y:1.0),
                        controlPoint2: CGPoint(x:1.0,y:0.0))

// 2
UISpringTimingParameters()

UISpringTimingParameters(dampingRatio: 0.8,
                      initialVelocity: CGVector(dx:1.0, dy: 0.0))

UISpringTimingParameters(mass: CGFloat, stiffness: CGFloat,
                      damping: CGFloat, initialVelocity velocity: CGVector)