大部分人或许觉得动画用UIView 或是CoreAnimation的动画效果，那为何还需要UIKit 中的UIDynamic？
答：UIDynamic 为使用者提供更符合现实效果的互动行为（比如：自由落体能量消耗的过程）
一、需求：请实现下图所示的动画效果(物理碰撞)
JJ's Animation.gif
二、上面引入过UIDynamic 可以实现碰撞的物理效果动画，how to start ?
- 在工程中导入UIKit，从Headers 找一些UIDynamic，发现了
UIDynamicAnimator.h,UIDynamicBehavior,UIDynamicItemBehavior - 既然是要动画效果 那就应该是
UIDynamicAnimator.h - 到
UIDynamicAnimator.h头文件去查看注释
// When you initialize a dynamic animator with this method, you should only associates views with your behaviors.
// the behaviors (and their dynamic items) that you add to the animator employ the reference view’s coordinate system.
- (instancetype)initWithReferenceView:(UIView *)view NS_DESIGNATED_INITIALIZER;
- 大概意思是使用这个初始化方法的时候，需要为你的试图关联behaviors
- what's the
behaviors? jump into defination 然而还不是很懂，UIDynamicBehavior,那就查看API (注意文档中的如下描述)。 - This parent class, UIDynamicBehavior, is inherited by the primitive dynamic behavior classes UIAttachmentBehavior, UICollisionBehavior, UIGravityBehavior, UIDynamicItemBehavior, UIPushBehavior, and UISnapBehavior.
- 文档中提到UIDynamicBehavior的父类，那么
UIDynamicBehavior父类(Dynamic 行为相关类)描述什么行为呢？- UIAttachmentBehavior：附着行为
- UICollisionBehavior：碰撞行为
- UIGravityBehavior：重力行为
- UIDynamicItemBehavior：动态元素行为
- UIPushBehavior：推行为
- UISnapBehavior：吸附行为
- 上述的各种行为可单独使用，也可以组合使用更复杂的动画效果。
解决方案的思路就引导到这边，也就可以实现上述需求。Dynamic 行为相关类的属性可自行研究。
三、解决方案。
- 上述需求的解决方案（我这边用的是6sP的模拟器奥，因为在设置floor的y坐标是600）
- 既然是球落地效果，必然有两个模拟对象：floor，basketBall
1.创建UIDynamicAnimator 对象
self.animator = [[UIDynamicAnimator alloc] initWithReferenceView:self.view];2.刚刚在API 看到了初始化UIDynamicAnimator需要关联一个或者多个行为
NSArray *animatorObjects = @[self.imageV1];
// 刚刚在API 看到了初始化UIDynamicAnimator需要关联一个或者多个行为
self.gravityBehav = [[UIGravityBehavior alloc] initWithItems:animatorObjects];
self.colision = [[UICollisionBehavior alloc] initWithItems:animatorObjects];
```
- 3.如果你想监听碰撞的状态，可以设置一下代理
```
self.colision.collisionDelegate = self;
```
- 4.设置碰撞边界
```
[self.colision addBoundaryWithIdentifier:@"boundaryLine" fromPoint:CGPointMake(0, 600) toPoint:CGPointMake(SCREENWITH, 600)];
```
- 5.设置动态行为参数
```
// 设置动态行为参数
UIDynamicItemBehavior *itemBehavior = [[UIDynamicItemBehavior alloc] initWithItems:animatorObjects];
// 设置弹性
[itemBehavior setElasticity:0.5];
```
- 6.行为创建了，别忘了给animator添加上
```
[self.animator addBehavior:self.gravityBehav];
[self.animator addBehavior:self.colision];
[self.animator addBehavior:itemBehavior];
```
### 三、下面代码只能说功能实现
- PS：以下代码不符合代码书写规范
```objc
//
// ViewController.m
// DynamicAnimation
//
// Created by JeversonJee on 16/5/27.
// Copyright © 2016年 JeversonJee. All rights reserved.
//
#import "ViewController.h"
#define SCREENWITH [UIScreen mainScreen].bounds.size.width
#define SCREENHEIGHT [UIScreen mainScreen].bounds.size.height
@interface ViewController ()<UICollisionBehaviorDelegate>
@property (nonatomic, strong) UIDynamicAnimator *animator;
@property (nonatomic, strong) UIGravityBehavior *gravityBehav;
@property (nonatomic, strong) UICollisionBehavior *colision;
@property (nonatomic, strong) UIImageView *imageV1;
@property (nonatomic, strong) UIImageView *imageV2;
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
[self jjCollisionBehav];
}
- (void)jjCollisionBehav {
// 创建碰撞需要的对象
[self jjCreateBall];
[self jjCreateFloor];
// 创建UIDynamicAnimator 对象
self.animator = [[UIDynamicAnimator alloc] initWithReferenceView:self.view];
NSArray *animatorObjects = @[self.imageV1];
// 刚刚在API 看到了初始化UIDynamicAnimator需要关联一个或者多个行为
self.gravityBehav = [[UIGravityBehavior alloc] initWithItems:animatorObjects];
self.colision = [[UICollisionBehavior alloc] initWithItems:animatorObjects];
// 这里设置代理是为了监听碰撞状态的，可以去了解一下代理方法
self.colision.collisionDelegate = self;
// 设置碰撞边界
[self.colision addBoundaryWithIdentifier:@"boundaryLine" fromPoint:CGPointMake(0, 600) toPoint:CGPointMake(SCREENWITH, 600)];
// 设置动态行为参数
UIDynamicItemBehavior *itemBehavior = [[UIDynamicItemBehavior alloc] initWithItems:animatorObjects];
// 设置弹性
[itemBehavior setElasticity:0.5];
// 创建了行为需要animator添加
[self.animator addBehavior:self.gravityBehav];
[self.animator addBehavior:self.colision];
[self.animator addBehavior:itemBehavior];
}
-(void)collisionBehavior:(UICollisionBehavior *)behavior endedContactForItem:(id<UIDynamicItem>)item withBoundaryIdentifier:(id<NSCopying>)identifier {
NSLog(@"collisionBehavior=%@", item);
NSString *identifierStr = [NSString stringWithFormat:@"%@", identifier];
NSLog(@"s=%@", identifier);
if ( [identifierStr isEqualToString:@"boundaryLine"] ) {
[self.imageV2 setBackgroundColor:[UIColor grayColor]];
[UIView animateWithDuration:2 animations:^(void){
[self.imageV2 setBackgroundColor:[UIColor grayColor]];
}];
}
}
-(void)jjCreateBall {
_imageV1 = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"basketBall"]];
_imageV1.frame = CGRectMake(100, 100, 60, 60);
[self.view addSubview:_imageV1];
}
- (void)jjCreateFloor {
_imageV2 = [[UIImageView alloc] init];
[_imageV2 setBackgroundColor:[UIColor grayColor]];
_imageV2.frame = CGRectMake(0, 600, SCREENWITH, SCREENHEIGHT - 400);
[self.view addSubview:_imageV2];
}
-(void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
@end
四、UIDynamicDemo：GitHub/jeversonjee点击下载
The last but not least：
1.如果想更好的玩转UIDynamics请查阅fancypixel有关Playing With UIDynamics in iOS 9
PS:1.录屏 Gif （for Mac）软件：GIPHY CAPTURE
2.那个boundary（边界）设置的适合下面的floor是一样高的，我选的图片是有白色背景的方形（Rect），没有把背景改成透明的，会感觉到球的底面没有和floor 重合的感觉。
