先看看摩拜貼紙的動畫：

知識點(diǎn)歸納：

• 使用重力行為
• 使用碰撞行為
• 使用彈力行為
• 使用屏幕旋轉(zhuǎn)的傳感器

代碼實(shí)現(xiàn)：

1. 創(chuàng)建若干個小球(UIImageView)

    NSMutableArray *ballViewArr = [NSMutableArray array];
    for(int i=0;i<imageArr.count;i++)
    {
        UIImageView * imgView = [[UIImageView alloc]initWithFrame:CGRectMake(arc4random()%((int)(self.view.bounds.size.width-diameter)), 0, diameter, diameter)];
        imgView.image = [UIImage imageNamed:imageArr[i]];
        imgView.layer.masksToBounds = YES;
        imgView.layer.cornerRadius = diameter/2;
        [self.view addSubview:imgView];
        
        [ballViewArr addObject:imgView];
    }

2.創(chuàng)建動畫的播放者

    //_animator為全局定義的，否則不會生效，self.view為力學(xué)參考系，動力效果才能生效
    _animator = [[UIDynamicAnimator alloc]initWithReferenceView:self.view];

3.創(chuàng)建動力行為，并賦給小球

    //添加重力
    _gravity = [[UIGravityBehavior alloc]initWithItems:ballViewArr];
    [_animator addBehavior:_gravity];
    
    //添加碰撞
    UICollisionBehavior *collision = [[UICollisionBehavior alloc]initWithItems:ballViewArr];
    collision.translatesReferenceBoundsIntoBoundary = YES;
    [_animator addBehavior:collision];
    
    //添加彈性
    UIDynamicItemBehavior *dyItem = [[UIDynamicItemBehavior alloc]initWithItems:ballViewArr];
    dyItem.allowsRotation = YES;
    dyItem.elasticity = 0.8;        //彈性系數(shù)
    [_animator addBehavior:dyItem];
    
    //還有很多behavior:UIAttachmentBehavior(附著行為)、UISnapBehavior(捕捉行為)、UIPushBehavior(推動行為)、UIDynamicItemBehavior(動力元素行為)

4.創(chuàng)建檢測屏幕旋轉(zhuǎn)的傳感器，并計(jì)算新的弧度給重力行為屬性賦值

-(void)initGyroManager
{
    self.motionManager = [[CMMotionManager alloc]init];
    self.motionManager.deviceMotionUpdateInterval = 0.01;
    
    [self.motionManager startDeviceMotionUpdatesToQueue:[NSOperationQueue mainQueue] withHandler:^(CMDeviceMotion * _Nullable motion, NSError * _Nullable error) {
        //返回至原點(diǎn)的方位角
        double rotation = atan2(motion.attitude.pitch, motion.attitude.roll);
        NSLog(@"rotation:%f",motion.attitude.pitch);
        self.gravity.angle = rotation;
    }];
}
-(void)dealloc
{
    [self.motionManager stopDeviceMotionUpdates];
}

這樣，代碼就搞定咯。另外可以參考：iOS進(jìn)階 - UIDynamic以及iOS的一些傳感器。

此篇博客的Demo地址