根據動畫效果需要分析動畫的實現就兩個重點，一個是下落，一個是彈跳，查看完整代碼和效果請 下載相關DEMO，DEMO對相關代碼進行了一定整理，現將部分關鍵代碼列出：

 一、下落過程－關鍵幀動畫

- (void)pointsAnimaton
{
    for (UIImageView *imageView in _itemsArray) {
        CGRect frontRect = imageView.frame;
        CGRect currentRect = [self realityCurrentRect];
        
        CGFloat cX = 0;
        CGFloat cY = 0;
        
        _useDeviationValue = _deviationValue + arc4random() % 5 * 3;//偏移基礎上添加隨機值
        
        CGFloat distance = (currentRect.origin.x + currentRect.size.width / 2.0 + _useDeviationValue) - (frontRect.origin.x + frontRect.size.width / 2.0);
        cX += frontRect.origin.x + frontRect.size.width / 2.0 + distance * 0.3;
        cY = frontRect.origin.y - 150;
        CAKeyframeAnimation *bounceAnimation = [CAKeyframeAnimation animationWithKeyPath:@"position"];//關鍵幀動畫
        CGMutablePathRef thePath = CGPathCreateMutable();
        bounceAnimation.delegate = self;
        CGPathMoveToPoint(thePath, NULL, frontRect.origin.x + frontRect.size.width / 2.0, imageView.center.y);
        //出界判斷
        CGFloat toX = currentRect.origin.x + currentRect.size.width / 2.0 + _useDeviationValue;
        if (toX > currentRect.origin.x + currentRect.size.width) {
            toX = currentRect.origin.x + currentRect.size.width;
        }
        if (toX < currentRect.origin.x) {
            toX = currentRect.origin.x;
        }
        CGPathAddQuadCurveToPoint(thePath, NULL, cX, cY, toX, currentRect.origin.y);
        bounceAnimation.path = thePath;
        bounceAnimation.duration = .6 + ((arc4random() % 3) * 0.04);//動畫時間（添加隨機性）
        bounceAnimation.fillMode = kCAFillModeForwards;//與removedOnCompletion = NO 共同作用，動畫停留在結束位置
        bounceAnimation.removedOnCompletion = NO;//與fillMode = kCAFillModeForwards 共同作用，動畫停留在結束位置
        [imageView.layer addAnimation:bounceAnimation forKey:@"move"];
    }
}

二、到達落點後的彈跳效果－力學行為

- (void)addBehaviour
{
    if (!_animator) {//力學行為容器
        _animator = [[UIDynamicAnimator alloc] initWithReferenceView:_referenceView];
        _animator.delegate = self;
    }else{
        [_animator removeAllBehaviors];
    }
    //重力行為
    if (!_gravity) {
        _gravity = [[UIGravityBehavior alloc] initWithItems:_itemsArray];
    }
    
    [_animator addBehavior:_gravity];
    
    CGRect currentRect =  [self realityBehaviourCurrentRect];//CGRectFromString(_framesArray[_currentIndex]);
    //碰撞行為
    if (!_collision) {
        _collision = [[UICollisionBehavior alloc]
                      initWithItems:_itemsArray];
        
        _collision.translatesReferenceBoundsIntoBoundary = NO;//是否與referenceView邊界碰撞
        _collision.collisionDelegate = self;
    }
    
    [_collision addBoundaryWithIdentifier:@"barrier" fromPoint:currentRect.origin
                                  toPoint:CGPointMake(currentRect.origin.x + currentRect.size.width, currentRect.origin.y)];
    
    [_animator addBehavior:_collision];
    
    if (!_itemBehaviour) {//行為限制
        _itemBehaviour = [[UIDynamicItemBehavior alloc] initWithItems:_itemsArray];
        _itemBehaviour.allowsRotation = NO;//是否允許旋轉
        _itemBehaviour.elasticity = 0.6;//彈力系數(0.0 ~ 1.0)
        _itemBehaviour.friction = 0.5;//摩擦系數(0.0 ~ 1.0)
    }
    [_animator addBehavior:_itemBehaviour];
    _needPush = YES;
}