UIDynamic－iOS中的物理引擎

1. 创建一个物理仿真器 设置仿真范围
2. 创建相应的物理仿真行为 添加物理仿真元素
3. 将物理仿真行为添加到仿真器中开始仿真

懒加载方式 创建物理仿真器

-  (UIDynamicAnimator *) animator
{
if(!_animator) {
_animator = [[UIDynamicAnimator alloc] initWithReferenceView:self.view];
}
return _animator;
}

创建相应的物理仿真行为

1. 模拟重力行为 UIGravityBehavior
   // 创建重力行为
   UIGravityBehavior *gravity = [[UIGravityBehavior alloc] init];
   // magnitude越大，速度增长越快
   gravity.magnitude = 100;
   // 添加元素 告诉仿真器哪些元素添加重力行为
   [gravity addItem:self.sxView];

   // 添加到仿真器中开始仿真
   [self.animator addBehavior:gravity];

2. 模拟碰撞行为 UICollisionBehavior
   // 1.创建重力行为
   UIGravityBehavior *gravity = [[UIGravityBehavior alloc] init];
   // magnitude越大，速度增长越快
   gravity.magnitude = 2;
   [gravity addItem:self.sxView];

   // 2.创建碰撞行为
   UICollisionBehavior *collision = [[UICollisionBehavior alloc] init];
   [collision addItem:self.sxView];
   [collision addItem:self.bigBlock];
   [collision addItem:self.smallBlock];
   // 设置碰撞的边界
   collision.translatesReferenceBoundsIntoBoundary = YES;
   // 如果觉得屏幕作为边界不好，可以自己设置一条边可以是普通的边
   // [collision addBoundaryWithIdentifier:@"line2" fromPoint:
   CGPointMake(self.view.frame.size.width, 0) toPoint:
   CGPointMake(self.view.frame.size.width, 400)];
   //也可以是个贝塞尔路径
   UIBezierPath *path = [UIBezierPath bezierPathWithOvalInRect:
   CGRectMake(0,150, self.view.frame.size.width, self.view.frame.size.width)];
   [collision addBoundaryWithIdentifier:@"circle" forPath:path];
   // 3.开始仿真
   [self.animator addBehavior:gravity];
   [self.animator addBehavior:collision];

3. 模拟捕捉行为 UISnapBehavior

   • (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
     {
     // 1.获得手指对应的触摸对象
     UITouch *touch = [touches anyObject];

     // 2.获得触摸点
     CGPoint point = [touch locationInView:self.view];

     // 3.创建捕捉行为
     UISnapBehavior *snap = [[UISnapBehavior alloc] initWithItem:self.sxView snapToPoint:point];
     // 防震系数，damping越大，振幅越小
     snap.damping = 1;

     // 4.清空之前的并再次开始
     [self.animator removeAllBehaviors];
     [self.animator addBehavior:snap];
     }