UIDynamicAnimator 是iOS7之后引入的一个动态库，用来模拟实现现实世界的物理模型，实现的动画有动感。主要模拟的物理行为有：UIGravityBehavior(重力)，UIAttachmentBehavior(吸附)，UISnapBehavior(震荡)，UIPushBehavior(推动)，UICollisionBehavior(碰撞)，UIDynamicItemBehavior(配置一些公用的属性，与其他的Dynamic Behavior共同配合)。
本文主要介绍一个未完待续的小动画，结合UIGravityBehavior、UISnapBehavior、UICollisionBehavior实现。
一、初始化UI
- (void)initSubViews {- (void)initSubViews {
[self.view addSubview:self.weiImageView];
[self.view addSubview:self.wanImageView];
[self.view addSubview:self.daiImageView];
[self.view addSubview:self.xuImageView];
[self.view addSubview:self.longmaoImageView];
_weiImageView.cy_originY = -100;
_wanImageView.cy_originY = -100;
_daiImageView.cy_originY = -100;
_xuImageView.cy_originY = -100;
}
初始化ImageView的时候，设置ImageView的frame是你想设置的位置，这里又设置各个frame的origin.y为0是为了实现掉落效果。
二、实现动画
- (void)animation {
//实现龙猫的晃动动画，设置龙猫不间断晃动
CAKeyframeAnimation *animation = [CAKeyframeAnimation animation];
animation.keyPath = @"transform.rotation";
animation.values = @[@(-20 / 180.0 * M_PI), @(10 / 180.0 * M_PI), @(-20 /180.0 * M_PI)];
animation.removedOnCompletion = NO;
animation.duration = 0.5;
animation.repeatCount = MAXFLOAT;
[self.longmaoImageView.layer addAnimation:animation forKey:nil];
//设置四个ImageView的吸附动画，由初始位置吸附到各个ImageView的center位置，每个ImageView 的路径不一样
UISnapBehavior *snap = [[UISnapBehavior alloc] initWithItem:_weiImageView snapToPoint:weiInitialPoint];
snap.damping = 1.0;
UISnapBehavior *snap1 = [[UISnapBehavior alloc] initWithItem:_wanImageView snapToPoint:wanInitialPoint];
snap1.damping = 1.0;
UISnapBehavior *snap2 = [[UISnapBehavior alloc] initWithItem:_daiImageView snapToPoint:daiInitialPoint];
snap2.damping = 1.0;
UISnapBehavior *snap3 = [[UISnapBehavior alloc] initWithItem:_xuImageView snapToPoint:xuInitialPoint];
snap3.damping = 1.0;
//重力效果，声明一个对象，可以循环加载
UIGravityBehavior *gravity = [[UIGravityBehavior alloc] init];
[gravity addItem:_weiImageView];
[gravity addItem:_wanImageView];
[gravity addItem:_daiImageView];
[gravity addItem:_xuImageView];
//弹性效果，这里设置碰撞类型collisionMode为碰撞所有
UICollisionBehavior *collision = [[UICollisionBehavior alloc] init];
collision.collisionMode = UICollisionBehaviorModeEverything;
[collision addItem:_weiImageView];
[collision addItem:_wanImageView];
[collision addItem:_daiImageView];
[collision addItem:_xuImageView];
//初始化 self.animator，self.animator的ReferenceView是所有子类View的父View，承载所有动画
//snap吸附动画的发生通过线程设置延时，展现出的效果有节奏
self.animator = [[UIDynamicAnimator alloc] initWithReferenceView:self.view];
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
[self.animator addBehavior:snap];
});
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.4 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
[self.animator addBehavior:snap1];
});
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.8 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
[self.animator addBehavior:snap2];
});
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1.2 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
[self.animator addBehavior:snap3];
});
}
三、细节补充
关于UICollisionBehavior的collisionMode的三种效果，可以参考文章
http://www.jianshu.com/p/2ca3b16026a5
另外附上本文Demo地址，感兴趣的小伙伴可以参考一下，如有不合理的地方欢迎指正！