UIDynamic物理仿真器

1、首先创建物理仿真器UIDynamicAnimator，并添加仿真范围ReferenceView

//使用懒加载创建仿真器，并使用当前view作为仿真区域
-(UIDynamicAnimator *)animator
{
    if (_animator == nil) {
        _animator = [[UIDynamicAnimator alloc] initWithReferenceView:self.view];
    }
    return _animator;
}

2、添加物理行为UIDynamicBehavior

物理行为有：

UIGravityBehavior：重力行为

UICollisionBehavior:碰撞行为

UISnapBehavior:捕捉行为

UIPushBehavior:推动行为

UIAttachmentBehavior:附着行为

UIDynamicItemBehavior:动力元素行为

//添加重力行为
UIGravityBehavior *gravity = [[UIGravityBehavior alloc] initWithItems:@[self.view1]];
[self.animator addBehavior:gravity];

//添加碰撞检测行为
UICollisionBehavior *collision = [[UICollisionBehavior alloc] initWithItems:@[self.view1,self.view2]];
    //将当前ReferenceView边界转换为碰撞检测边界
    //    collision.translatesReferenceBoundsIntoBoundary = YES;
    //手动画线作为碰撞检测边界
    //        [collision addBoundaryWithIdentifier:@"line" fromPoint:CGPointMake(0, 200) toPoint:CGPointMake(320, 400)];

   //通过贝塞尔曲线绘制碰撞边界    
    UIBezierPath *path = [UIBezierPath bezierPathWithOvalInRect:CGRectMake(0, 0, 320, 500)];
    [collision addBoundaryWithIdentifier:@"circle" forPath:path];
    [self.animator addBehavior:collision];    

//捕捉行为    
-(void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
    UITouch *touch = [touches anyObject];
    CGPoint point = [touch locationInView:touch.view];
    UISnapBehavior *snap = [[UISnapBehavior alloc] initWithItem:self.view1 snapToPoint:point];
    UICollisionBehavior *collision = [[UICollisionBehavior alloc] initWithItems:@[self.view1,self.view2]];
    collision.translatesReferenceBoundsIntoBoundary = YES;
    
    //能够多次调用捕捉行为
    [self.animator removeAllBehaviors];
    [self.animator addBehavior:collision];
    [self.animator addBehavior:snap];
}