UIDynamic--动力元素行为:UIDynamicItemBehavior

属性分析:

 @property (nonatomic, readonly, copy) NSArray* items;  

 @property (readwrite, nonatomic) CGFloat elasticity; // Usually between 0 (inelastic) and 1 (collide elastically) 弹性系数 在0~1之间
 @property (readwrite, nonatomic) CGFloat friction; // 0 being no friction between objects slide along each other 摩擦力系数
 @property (readwrite, nonatomic) CGFloat density; // 1 by default 跟size大小相关，计算物体块的质量。
 @property (readwrite, nonatomic) CGFloat resistance; // 0: no velocity damping 阻力系数
 @property (readwrite, nonatomic) CGFloat angularResistance; // 0: no angular velocity damping 旋转阻力
 @property (readwrite, nonatomic) BOOL allowsRotation; // force an item to never rotate  是否能旋转

代码:

 //
 //  YFDynamicItemViewController.m
 //  BigShow1949
 //
 //  Created by apple on 16/8/25.
 //  Copyright © 2016年 BigShowCompany. All rights reserved.
 //

 #import "YFDynamicItemViewController.h"

 @interface YFDynamicItemViewController ()
 @property(nonatomic,strong)UIDynamicAnimator *animator;
 @property (nonatomic, strong) UIView *redView;

 @end

 @implementation YFDynamicItemViewController

 - (void)viewDidLoad {

     [super viewDidLoad];
     self.view.backgroundColor = [UIColor whiteColor];

     UIView *redView = [[UIView alloc] init];
     redView.frame = CGRectMake(, , , );
     redView.backgroundColor = [UIColor redColor];
     self.redView = redView;
     [self.view addSubview:redView];
 }

 - (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {

     [self testGravityAndCollsion];
 }
 /**
  *  重力行为+碰撞检测
  */
 -(void)testGravityAndCollsion
 {
     //1.重力行为
     UIGravityBehavior *gravity=[[UIGravityBehavior alloc]init];
     [gravity addItem:self.redView];

     //2碰撞检测行为
     UICollisionBehavior *collision=[[UICollisionBehavior alloc]init];
     [collision addItem:self.redView];
     //让参照视图的边框成为碰撞检测的边界
     collision.translatesReferenceBoundsIntoBoundary=YES;

     // 动力元素行为
     UIDynamicItemBehavior * itemBehavior = [[UIDynamicItemBehavior alloc] initWithItems:@[self.redView]];
     itemBehavior.elasticity = 1.2;
     itemBehavior.friction = .;
     itemBehavior.density = ;
     itemBehavior.resistance = ; // 阻力系数
     itemBehavior.allowsRotation = NO;
     itemBehavior.angularResistance = ;

     //3.执行仿真
     [self.animator addBehavior:gravity];
     [self.animator addBehavior:collision];
     [self.animator addBehavior:itemBehavior];
 }

 -(UIDynamicAnimator *)animator
 {
     if (_animator==nil) {
         //创建物理仿真器（ReferenceView:参照视图，设置仿真范围）
         self.animator=[[UIDynamicAnimator alloc]initWithReferenceView:self.view];
     }
     return _animator;
 }

 @end