当两个图像视图与动画一起移动时，如何识别它们的碰撞？

Question

我正在努力在两个视图发生碰撞时发出警报，这里我使用两个图像视图在不同的方向上移动，它们将在一个点发生碰撞。我使用基本的动画代码将这些图像沿各自的方向移动。（注意：-不仅像下图一样，但是如果它们在方面发生碰撞，我们需要显示警报）

Answer 1

如果使用标准视图动画（例如基于块的animateWithDuration），您可以设置一个CADisplayLink（有点像计时器，但每次显示更新时都会调用）然后比较@987654325 @ 两个视图的值，看看它们是否相交。不过，诀窍是，在动画期间，视图的 frame 是“最终目标”帧，因此如果您想要在动画进行时保持原样的 frame，您可以查看它的“表示层”。

- (void)startDisplayLink
{
    self.displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(handleDisplayLink:)];
    [self.displayLink addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSRunLoopCommonModes];
}

- (void)stopDisplayLink
{
    [self.displayLink invalidate];
    self.displayLink = nil;
}

- (void)handleDisplayLink:(CADisplayLink *)displayLink
{
    CALayer *view1PresentationLayer = self.view1.layer.presentationLayer;
    CALayer *view2PresentationLayer = self.view2.layer.presentationLayer;

    if (CGRectIntersectsRect(view1PresentationLayer.frame, view2PresentationLayer.frame)) {

        NSLog(@"collision");                              // report the collision; show alert if you want

        [self.view1.layer removeAllAnimations];           // stop the animation if you want
        [self.view2.layer removeAllAnimations];

        self.view1.frame = view1PresentationLayer.frame;  // but make sure to reset the frame to be the current position
        self.view2.frame = view2PresentationLayer.frame;

        [self stopDisplayLink];                           // stop the display link if we don't need it any more
    }
}

在上述方法中，我假设您想停止动画（这不仅涉及删除动画，还包括重置最终目的地以反映当前视图的位置），但可以做任何您想做的事情。

因此，您可以启动显示链接，启动动画，显示链接选择器方法会告诉我们是否有碰撞：

[self startDisplayLink];

[UIView animateWithDuration:1.0 animations:^{
    self.view1.frame = CGRectMake(...);
    self.view2.frame = CGRectMake(...);
}];

---

注意，在 iOS 7 中，您可能需要查看 UIKit Dynamics，您可以在其中添加行为来驱动视图的移动，还可以定义 UICollisionBehavior 来识别何时发生这种碰撞。使用 UIKit Dynamics 可能超出了这个问题的范围，但您应该参考 Apple 的 WWDC 2013 视频 Getting Started with UIKit Dynamics 和 Advanced Techniques with UIKit Dynamics。

但是，例如，在 iOS 7 中，您可以放弃 animateWithDuration，而是使用 UIKit Dynamics 进行动画处理，您可以在其中告诉两个视图捕捉到屏幕上的特定位置，但在它们发生碰撞时进行检测：

self.animator = [[UIDynamicAnimator alloc] initWithReferenceView:self.view];

UIDynamicItemBehavior *itemBehavior = [[UIDynamicItemBehavior alloc] initWithItems:@[self.view1, self.view2]];
itemBehavior.allowsRotation = NO;
itemBehavior.resistance = 10.0;  // you can change this to affect the speed of the attachment behaviors
[self.animator addBehavior:itemBehavior];

UISnapBehavior *snap1 = [[UISnapBehavior alloc] initWithItem:self.view1 snapToPoint:newPoint1];
[self.animator addBehavior:snap1];

UISnapBehavior *snap2 = [[UISnapBehavior alloc] initWithItem:self.view2 snapToPoint:newPoint2];
[self.animator addBehavior:snap2];

// You can, alternatively use the following attachment behaviors, instead of the above
// snap behaviors, and you can then use resistance to control the speed with which they move
//
// UIAttachmentBehavior *attachment1 = [[UIAttachmentBehavior alloc] initWithItem:self.view1 attachedToAnchor:self.view1.center];
// [self.animator addBehavior:attachment1];
// attachment1.frequency = 1.0;
// attachment1.anchorPoint = newPoint1;
//
// UIAttachmentBehavior *attachment2 = [[UIAttachmentBehavior alloc] initWithItem:self.view2 attachedToAnchor:self.view2.center];
// [self.animator addBehavior:attachment2];
// attachment2.frequency = 1.0;
// attachment2.anchorPoint = newPoint2;

UICollisionBehavior *collision = [[UICollisionBehavior alloc] initWithItems:@[self.view1, self.view2]];
collision.collisionDelegate = self;
[self.animator addBehavior:collision];

并且有一个UICollisionBehaviorDelegate 方法可以在发生碰撞时执行某些操作，例如删除行为，有效地结束动画：

- (void)collisionBehavior:(UICollisionBehavior *)behavior beganContactForItem:(id<UIDynamicItem>)item1 withItem:(id<UIDynamicItem>)item2 atPoint:(CGPoint)p
{
    [self.animator removeAllBehaviors];  // for example, if they collide, you could remove the behaviors so they stop

    // show alert if you want to
}

Answer 2

如果您的目标是 iOS 7 及更高版本，那么您可以查看 UIKit Dynamics

https://developer.apple.com/library/ios/samplecode/DynamicsCatalog/Introduction/Intro.html