一、简单介绍
1.什么是UIDynamic
UIDynamic是从iOS 7开始引入的一种新技术，隶属于UIKit框架可以认为是一种物理引擎，能模拟和仿真现实生活中的物理现象如：重力、弹性碰撞等现象
2.物理引擎的价值
广泛用于游戏开发，经典成功案例是“愤怒的小鸟”,让开发人员可以在远离物理学公式的情况下，实现炫酷的物理仿真效果提高了游戏开发效率，产生更多优秀好玩的物理仿真游戏
3.知名的2D物理引擎
Box2d
Chipmunk
二、使用步骤
要想使用UIDynamic来实现物理仿真效果，大致的步骤如下:
1.创建一个物理仿真器（顺便设置仿真范围）
2.创建相应的物理仿真行为（顺便添加物理仿真元素）
3.将物理仿真行为添加到物理仿真器中开始仿真
三、相关说明
1.三个概念
- 谁要进行物理仿真？
物理仿真元素（Dynamic Item） - 执行怎样的物理仿真效果？怎样的动画效果？
物理仿真行为（Dynamic Behavior） - 让物理仿真元素执行具体的物理仿真行为
物理仿真器（Dynamic Animator）
2.物理仿真元素
注意：
不是任何对象都能做物理仿真元素
不是任何对象都能进行物理仿真
物理仿真元素要素：
任何遵守了UIDynamicItem协议的对象
UIView默认已经遵守了UIDynamicItem协议，因此任何UI控件都能做物理仿真
UICollectionViewLayoutAttributes类默认也遵守UIDynamicItem协议
3.物理仿真行为
（1）UIDynamic提供了以下几种物理仿真行为
- UIGravityBehavior：重力行为
UICollisionBehavior：碰撞行为
UISnapBehavior：捕捉行为
UIPushBehavior：推动行为
UIAttachmentBehavior：附着行为
UIDynamicItemBehavior：动力元素行为
（2）物理仿真行为须知
上述所有物理仿真行为都继承自UIDynamicBehavior，所有的UIDynamicBehavior都可以独立进行组合使用多种行为时，可以实现一些比较复杂的效果
4.物理仿真器
（1）物理仿真器须知
它可以让物理仿真元素执行物理仿真行为
它是UIDynamicAnimator类型的对象
（2）UIDynamicAnimator的初始化
- (instancetype)initWithReferenceView:(UIView *)view;
`</pre>
view参数：是一个参照视图，表示物理仿真的范围
5.物理仿真器的说明
（1）UIDynamicAnimator的常见方法
<pre>`//移除之前添加过的所有物理仿真行为
- (void)addBehavior:(UIDynamicBehavior *)behavior;
//移除之前添加过的所有物理仿真行为
- (void)removeBehavior:(UIDynamicBehavior *)behavior;
//添加1个物理仿真行为
- (void)removeAllBehaviors;
`</pre>
（2）UIDynamicAnimator的常见属性
<pre>` //参照视图
@property (nonatomic, readonly) UIView* referenceView;
//添加到物理仿真器中的所有物理仿真行为
@property (nonatomic, readonly, copy) NSArray* behaviors;
//是否正在进行物理仿真
@property (nonatomic, readonly, getter = isRunning) BOOL running;
//代理对象（能监听物理仿真器的仿真过程，比如开始和结束）
@property (nonatomic, assign) id
`</pre>
### 四、案例介绍
**先看效果吧**
- UIGravityBehavior：重力行为
UICollisionBehavior：碰撞行为
UISnapBehavior：捕捉行为
UIPushBehavior：推动行为
复合效果
最后是代码
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144<pre>`@interface SecondViewController : UIViewController@property (weak, nonatomic) IBOutlet UIView *blueView;@property (weak, nonatomic) IBOutlet UIView *orangeView;@property (weak, nonatomic) IBOutlet UISegmentedControl *segmented;@property (weak, nonatomic) IBOutlet UIView *redView;@property (nonatomic,strong) UIDynamicAnimator *animator;@end@interface SecondViewController ()@property (nonatomic,strong)UISnapBehavior *snapBehavior;@property (nonatomic,strong)UIPushBehavior *pushBehavior;@property (nonatomic,strong)UIAttachmentBehavior *attachmentBehavior;@end@implementation SecondViewController- (void)viewDidLoad {[super viewDidLoad];self.blueView.transform = CGAffineTransformMakeRotation(M_PI_4);self.segmented.transform = CGAffineTransformMakeRotation(-M_PI / 8);if (!_pushBehavior) {_pushBehavior = [[UIPushBehavior alloc]initWithItems:@[_blueView] mode:UIPushBehaviorModeContinuous];}_pushBehavior.active = YES;_pushBehavior.pushDirection = CGVectorMake(10.0f, 10.0f);_pushBehavior.magnitude = 1.0f;[self.animator addBehavior:_pushBehavior];}- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent: (UIEvent *)event {_pushBehavior.active = NO;//创建重力行为UIGravityBehavior *gravityBehavior = [[UIGravityBehavior alloc]init];[gravityBehavior addItem:self.blueView];[gravityBehavior addItem:self.orangeView];[gravityBehavior addItem:self.segmented];gravityBehavior.gravityDirection = CGVectorMake(-0.3f, 1.0f);//加速度gravityBehavior.magnitude = 3;//创建碰撞行为UICollisionBehavior *collisionBehavior = [[UICollisionBehavior alloc]init];//碰撞类型为元素和边界collisionBehavior.collisionMode = UICollisionBehaviorModeEverything;CGFloat Y = self.view.frame.size.height - CGRectGetHeight(self.redView.frame);CGFloat X = self.view.frame.size.width;CGFloat height = self.view.frame.size.height;//设置红色的View为底边界,左边框跟右边框作为边界[collisionBehavior addBoundaryWithIdentifier:@"collision1" fromPoint:CGPointMake(0,Y) toPoint:CGPointMake(X, Y)];[collisionBehavior addBoundaryWithIdentifier:@"collision2" fromPoint:CGPointMake(0, 0) toPoint:CGPointMake(0, height)];[collisionBehavior addBoundaryWithIdentifier:@"collision3" fromPoint:CGPointMake(X,0) toPoint:CGPointMake(X, height)];[collisionBehavior addItem:self.blueView];[collisionBehavior addItem:self.segmented];[collisionBehavior addItem:self.orangeView];[self.animator addBehavior:collisionBehavior];[self.animator addBehavior:gravityBehavior];UIDynamicItemBehavior *itemBehavior = [[UIDynamicItemBehavior alloc] initWithItems:@[self.blueView]];[itemBehavior setElasticity:0.5];[self.animator addBehavior:itemBehavior];UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc]initWithTarget:self action:@selector(tapGesture:)];[self.view addGestureRecognizer:tap];}- (void)tapGesture:(UITapGestureRecognizer *)gesture{CGPoint tapPoint = [gesture locationInView:self.view];if (_snapBehavior) {[self.animator removeBehavior:_snapBehavior];_snapBehavior = nil;}_snapBehavior = [[UISnapBehavior alloc]initWithItem:self.blueView snapToPoint:tapPoint];_snapBehavior.action = ^(){NSLog(@"UISnapBehavior 在执行");};_snapBehavior.damping = 0.9;[self.animator addBehavior:_snapBehavior];}- (UIDynamicAnimator *)animator{if (_animator == nil) {_animator = [[UIDynamicAnimator alloc]init];}return _animator;}- (void)panGestureRecognizer:(UIPanGestureRecognizer *)gesture{CGPoint location = [gesture locationInView:self.view];CGPoint imageLocation = [gesture locationInView:self.orangeView];switch (gesture.state) {case UIGestureRecognizerStateBegan:{NSLog(@"touch position %@",NSStringFromCGPoint(location));NSLog(@"loction in image %@",NSStringFromCGPoint(imageLocation));[self.animator removeAllBehaviors];UIOffset centerOffset = UIOffsetMake(imageLocation.x - CGRectGetMidX(self.orangeView.bounds), imageLocation.y - CGRectGetMidY(self.orangeView.bounds));_attachmentBehavior = [[UIAttachmentBehavior alloc]initWithItem:self.orangeView offsetFromCenter:centerOffset attachedToAnchor:location];_attachmentBehavior.damping = 0.5;_attachmentBehavior.frequency = 0.8;[self.animator addBehavior:_attachmentBehavior];}break;case UIGestureRecognizerStateEnded:{[self.animator removeBehavior:_attachmentBehavior];}break;default:{[_attachmentBehavior setAnchorPoint:[gesture locationInView:self.view]];}break;}}- (void)didReceiveMemoryWarning {[super didReceiveMemoryWarning];// Dispose of any resources that can be recreated.}/*#pragma mark - Navigation// In a storyboard-based application, you will often want to do a little preparation before navigation- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {// Get the new view controller using [segue destinationViewController].// Pass the selected object to the new view controller.}*/@end
UIKit动力学的部分介绍完了.
最开始项目中只是用到了重力跟碰撞行为,参考学习了:UIDynamic 详细用法 中的案例.然后自己又展开了解了下UIKit动力学的知识,把捕捉行为,推动行为加了进去,做个完善.整理了一下.就是这样.