UIkit Dynamics是UIkit的一套基于现实世界物理驱动的一套交互体系，包含了我们常见的物理知识现象，如重力、碰撞、弹力等效果。而UIKit Dynamice提供了一整套逼真的物理动作，在实现一些逼真的物理效果的时事倍功半。
有四个概念我们来稍微描述一下：
- UIDynamicItem 就是物理体系可以影响到的物体，像现实世界的桌子、椅子。在ios我们常见的UI控件像UIButton、UIView等实现了该接口。
- UIDynamicBehavior 一个行为，像重力或者弹性、吸附等效果
- UIDynamicAnimator 一个动画执行者，所有的行为都可以加入这个执行者，重力+碰撞就可以模拟高空坠落拉！
- referenceView 参照体系，就像现实世界的参照物。
一、重力行为UIGravityBehavior
var animator : UIDynamicAnimator!
override func viewDidLoad() {
super.viewDidLoad()
//box
let box : UIView = UIView(frame: CGRectMake(135, 80, 50, 50))
box.backgroundColor = UIColor.grayColor()
self.view.backgroundColor = UIColor.whiteColor()
self.view.addSubview(box)
//参照物为背景view
self.animator = UIDynamicAnimator(referenceView: self.view)
//为box添加重力行为
let gravity = UIGravityBehavior(items: [box])
//执行动画
self.animator.addBehavior(gravity)
}
这里注意把animator声明为类的成员变量，不然animator在viewDidLoad后就释放内存引用，就没有什么重力效果了。
GIF效果图
我们可以设置重力的向量，大小和方向就是坠落的方向和下坠加速度了。
<code>gravity.gravityDirection = CGVector(dx: 0, dy: 5)</code>
二、碰撞行为UICollisionBehavior
就这么无休止的坠落深渊未免也太无聊了吧，我们来让那个它跟屏幕下方进行碰撞。
var animator : UIDynamicAnimator!
override func viewDidLoad() {
super.viewDidLoad()
//box
let box : UIView = UIView(frame: CGRectMake(135, 80, 50, 50))
box.backgroundColor = UIColor.grayColor()
self.view.backgroundColor = UIColor.whiteColor()
self.view.addSubview(box)
//参照物为背景view
self.animator = UIDynamicAnimator(referenceView: self.view)
//为box添加重力行为
let gravity = UIGravityBehavior(items: [box])
//执行动画
self.animator.addBehavior(gravity)
GIF效果图
三、连线行为UIAttachmentBehavior
连线就是两个物体之间进行连接或者一个物体跟一个锚点之间连接。
参数说明：UIAttachmentBehavior(item: offsetFromCenter: attachedToAnchor: )
item:物理体系可以影响到的物体
offsetFromCenter:物体中心偏移
-
attachedToAnchor:跟物体相连的锚点
var animator : UIDynamicAnimator! override func viewDidLoad() { super.viewDidLoad() animator = UIDynamicAnimator(referenceView: self.view) //静止的box let staticBox = UIView(frame: CGRectMake(50, 50, 50, 50)) staticBox.backgroundColor = UIColor.redColor() staticBox.layer.cornerRadius = 5 ; //下坠的box let dynamicBox = UIView(frame: CGRectMake(250, 50, 50, 50)) dynamicBox.backgroundColor = UIColor.grayColor() dynamicBox.layer.cornerRadius = 5 ; //为dynamicBox添加重力行为 let cravity = UIGravityBehavior(items: [dynamicBox]) //为dynamicBox添加连线行为 let attachment = UIAttachmentBehavior(item: dynamicBox, offsetFromCenter: UIOffsetMake(0, 0), attachedToAnchor: CGPointMake(staticBox.center.x, staticBox.center.y)) //为dynamicBox添加碰撞行为 let collision = UICollisionBehavior(items: [dynamicBox]) collision.translatesReferenceBoundsIntoBoundary = true self.view.addSubview(staticBox) self.view.addSubview(dynamicBox) animator.addBehavior(cravity) animator.addBehavior(attachment) animator.addBehavior(collision) }
GIF效果图
想让“绳子”有弹性加上这段：<code>attachment.frequency = 1</code>
四、吸附行为UISnapBehavior
很有趣的“牛皮糖”效果
var animator : UIDynamicAnimator!
let tapGesture = UITapGestureRecognizer()
var box:UIView!
override func viewDidLoad() {
super.viewDidLoad()
//添加手势，轻触self.view，
self.tapGesture.addTarget(self, action: "tappedView")
self.view.userInteractionEnabled = true ;
self.view.addGestureRecognizer(tapGesture)
self.animator = UIDynamicAnimator(referenceView: self.view)
// Do any additional setup after loading the view, typically from a nib.
//物体
self.box = UIView(frame: CGRectMake(110, 50, 100, 100))
box.backgroundColor = UIColor.grayColor()
box.layer.cornerRadius = 5
self.view.addSubview(box)
}
//手势回调方法
func tappedView(){
let point = self.tapGesture.locationInView(self.view)
self.animator.removeAllBehaviors()
let snap = UISnapBehavior(item: self.box, snapToPoint: point)
self.animator.addBehavior(snap)
}
GIF效果图
四、推力UIPushBehavior
为物体施加一个外力，遵循力的合成
var box : UIView!
var animator : UIDynamicAnimator!
var push : UIPushBehavior!
let tapGetsture = UITapGestureRecognizer()
override func viewDidLoad() {
super.viewDidLoad()
self.animator = UIDynamicAnimator(referenceView: self.view)
//self.view加入轻触手势
self.tapGetsture.addTarget(self, action: "tappedView")
self.view.userInteractionEnabled = true
self.view.addGestureRecognizer(tapGetsture)
//box
self.box = UIView(frame: CGRectMake(110, 234, 100, 100))
self.box.layer.cornerRadius = 5 ;
self.box.backgroundColor = UIColor.grayColor()
//加入box
self.view.addSubview(self.box)
//碰撞
let collision = UICollisionBehavior(items: [box])
collision.setTranslatesReferenceBoundsIntoBoundaryWithInsets(UIEdgeInsets(top: self.topLayoutGuide.length, left: 0, bottom: self.bottomLayoutGuide.length, right: 0))
//推力
self.push = UIPushBehavior(items: [self.box], mode: UIPushBehaviorMode.Instantaneous)
self.push.angle = 0
self.push.magnitude = 0 ;
//加入行为
self.animator.addBehavior(self.push)
self.animator.addBehavior(collision)
}
//轻触手势
func tappedView(){
let tapPoint = self.tapGetsture.locationInView(self.view)
let centerPoint = CGPointMake(self.box.center.x, self.box.center.y)
//角度和大小
let angle = atan2(tapPoint.y - centerPoint.y, tapPoint.x - centerPoint.x)
var distance = sqrtf(powf(Float(tapPoint.x - centerPoint.x),2.0) + powf(Float(tapPoint.y - centerPoint.y),2))
distance = min(distance, 100.00)
self.push.setAngle(angle, magnitude: CGFloat(distance/100))
//每次更改push属性时，push都会变为不可活动状态，需要手动更改active为true
self.push.active = true ;
}
GIF效果图
