实现UIKitDynamics以将视图拖离屏幕

Question

我正在尝试找出与Jelly的应用程序类似的工具UIKit Dynamics(特别是向下滑动以在屏幕外拖动视图).

看动画:http://vimeo.com/83478484(@ 1:17)

我理解UIKit Dynamics是如何工作的,但是没有很好的物理背景,因此无法梳理不同的行为以获得理想的结果!

Answer 1

这种拖动可以通过UIAttachmentBehavior创建附件行为的位置来完成UIGestureRecognizerStateBegan,更改锚点UIGestureRecognizerStateChanged.当用户进行平移手势时,这实现了旋转拖动.

一旦UIGestureRecognizerStateEnded你可以删除UIAttachmentBehavior,但随后应用一个UIDynamicItemBehavior让动画无缝继续使用相同的线性和角速度,用户在放开它时拖动它(不要忘记使用一个action块来确定何时视图不再与superview相交,因此你可以删除动态行为,也可以删除视图.或者,如果您的逻辑确定要将其返回到原始位置,则可以使用a UISnapBehavior来执行此操作.

坦率地说,在这个短片的基础上,确切地确定他们正在做什么有点困难,但这些是基本的构建块.

例如,假设您创建了一些想要拖离屏幕的视图:

UIView *viewToDrag = [[UIView alloc] initWithFrame:...];
viewToDrag.backgroundColor = [UIColor lightGrayColor];
[self.view addSubview:viewToDrag];

UIGestureRecognizer *pan = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handlePan:)];
[viewToDrag addGestureRecognizer:pan];

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

然后,您可以创建一个手势识别器将其拖离屏幕:

- (void)handlePan:(UIPanGestureRecognizer *)gesture {
    static UIAttachmentBehavior *attachment;
    static CGPoint               startCenter;

    // variables for calculating angular velocity

    static CFAbsoluteTime        lastTime;
    static CGFloat               lastAngle;
    static CGFloat               angularVelocity;

    if (gesture.state == UIGestureRecognizerStateBegan) {
        [self.animator removeAllBehaviors];

        startCenter = gesture.view.center;

        // calculate the center offset and anchor point

        CGPoint pointWithinAnimatedView = [gesture locationInView:gesture.view];

        UIOffset offset = UIOffsetMake(pointWithinAnimatedView.x - gesture.view.bounds.size.width / 2.0,
                                       pointWithinAnimatedView.y - gesture.view.bounds.size.height / 2.0);

        CGPoint anchor = [gesture locationInView:gesture.view.superview];

        // create attachment behavior

        attachment = [[UIAttachmentBehavior alloc] initWithItem:gesture.view
                                               offsetFromCenter:offset
                                               attachedToAnchor:anchor];

        // code to calculate angular velocity (seems curious that I have to calculate this myself, but I can if I have to)

        lastTime = CFAbsoluteTimeGetCurrent();
        lastAngle = [self angleOfView:gesture.view];

        typeof(self) __weak weakSelf = self;

        attachment.action = ^{
            CFAbsoluteTime time = CFAbsoluteTimeGetCurrent();
            CGFloat angle = [weakSelf angleOfView:gesture.view];
            if (time > lastTime) {
                angularVelocity = (angle - lastAngle) / (time - lastTime);
                lastTime = time;
                lastAngle = angle;
            }
        };

        // add attachment behavior

        [self.animator addBehavior:attachment];
    } else if (gesture.state == UIGestureRecognizerStateChanged) {
        // as user makes gesture, update attachment behavior's anchor point, achieving drag 'n' rotate

        CGPoint anchor = [gesture locationInView:gesture.view.superview];
        attachment.anchorPoint = anchor;
    } else if (gesture.state == UIGestureRecognizerStateEnded) {
        [self.animator removeAllBehaviors];

        CGPoint velocity = [gesture velocityInView:gesture.view.superview];

        // if we aren't dragging it down, just snap it back and quit

        if (fabs(atan2(velocity.y, velocity.x) - M_PI_2) > M_PI_4) {
            UISnapBehavior *snap = [[UISnapBehavior alloc] initWithItem:gesture.view snapToPoint:startCenter];
            [self.animator addBehavior:snap];

            return;
        }

        // otherwise, create UIDynamicItemBehavior that carries on animation from where the gesture left off (notably linear and angular velocity)

        UIDynamicItemBehavior *dynamic = [[UIDynamicItemBehavior alloc] initWithItems:@[gesture.view]];
        [dynamic addLinearVelocity:velocity forItem:gesture.view];
        [dynamic addAngularVelocity:angularVelocity forItem:gesture.view];
        [dynamic setAngularResistance:1.25];

        // when the view no longer intersects with its superview, go ahead and remove it

        typeof(self) __weak weakSelf = self;

        dynamic.action = ^{
            if (!CGRectIntersectsRect(gesture.view.superview.bounds, gesture.view.frame)) {
                [weakSelf.animator removeAllBehaviors];
                [gesture.view removeFromSuperview];

                [[[UIAlertView alloc] initWithTitle:nil message:@"View is gone!" delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil] show];
            }
        };
        [self.animator addBehavior:dynamic];

        // add a little gravity so it accelerates off the screen (in case user gesture was slow)

        UIGravityBehavior *gravity = [[UIGravityBehavior alloc] initWithItems:@[gesture.view]];
        gravity.magnitude = 0.7;
        [self.animator addBehavior:gravity];
    }
}

- (CGFloat)angleOfView:(UIView *)view
{
    // http://stackoverflow.com/a/2051861/1271826

    return atan2(view.transform.b, view.transform.a);
}

这会产生(如果不向下拖动则显示快照行为,如果成功将其向下拖动则显示动态行为):

这只是一个演示的外壳,但是它说明了UIAttachmentBehavior在平移手势期间使用a,UISnapBehavior如果你想要反转手势的动画,你可以使用a ,但是用它UIDynamicItemBehavior来完成拖动它的动画,离开屏幕,但UIAttachmentBehavior尽可能顺利地从最终动画转换到最终动画.我还在最后的同时添加了一点引力,UIDynamicItemBehavior以便它平滑地从屏幕加速(所以它不会花太长时间).

根据需要自定义.值得注意的是,该平移手势处理程序非常笨重,我可能会考虑创建一个自定义识别器来清理该代码.但希望这说明了使用UIKit Dynamics将视图拖离屏幕底部的基本概念.

Answer 2

@Rob 的回答很棒（点赞！），但我会删除手动角速度计算，让 UIDynamics 使用UIPushBehavior. 只需设置目标偏移量，UIPushBehaviorUIDynamics 就会为你做旋转计算工作。

从@Rob 的相同设置开始：

UIView *viewToDrag = [[UIView alloc] initWithFrame:...];
viewToDrag.backgroundColor = [UIColor lightGrayColor];
[self.view addSubview:viewToDrag];

UIGestureRecognizer *pan = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handlePan:)];
[viewToDrag addGestureRecognizer:pan];

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

但是调整手势识别器处理程序以使用 UIPushBehavior

- (void)handlePan:(UIPanGestureRecognizer *)gesture {
    static UIAttachmentBehavior *attachment;
    static CGPoint startCenter;

    if (gesture.state == UIGestureRecognizerStateBegan) {
        [self.animator removeAllBehaviors];

        startCenter = gesture.view.center;

        // calculate the center offset and anchor point

        CGPoint pointWithinAnimatedView = [gesture locationInView:gesture.view];

        UIOffset offset = UIOffsetMake(pointWithinAnimatedView.x - gesture.view.bounds.size.width / 2.0,
                                       pointWithinAnimatedView.y - gesture.view.bounds.size.height / 2.0);

        CGPoint anchor = [gesture locationInView:gesture.view.superview];

        // create attachment behavior

        attachment = [[UIAttachmentBehavior alloc] initWithItem:gesture.view
                                               offsetFromCenter:offset
                                               attachedToAnchor:anchor];

        // add attachment behavior

        [self.animator addBehavior:attachment];
    } else if (gesture.state == UIGestureRecognizerStateChanged) {
        // as user makes gesture, update attachment behavior's anchor point, achieving drag 'n' rotate

        CGPoint anchor = [gesture locationInView:gesture.view.superview];
        attachment.anchorPoint = anchor;
    } else if (gesture.state == UIGestureRecognizerStateEnded) {
        [self.animator removeAllBehaviors];

        CGPoint velocity = [gesture velocityInView:gesture.view.superview];

        // if we aren't dragging it down, just snap it back and quit

        if (fabs(atan2(velocity.y, velocity.x) - M_PI_2) > M_PI_4) {
            UISnapBehavior *snap = [[UISnapBehavior alloc] initWithItem:gesture.view snapToPoint:startCenter];
            [self.animator addBehavior:snap];

            return;
        }

        // otherwise, create UIPushBehavior that carries on animation from where the gesture left off

        CGFloat velocityMagnitude = sqrtf((velocity.x * velocity.x) + (velocity.y * velocity.y));
        UIPushBehavior *pushBehavior = [[UIPushBehavior alloc] initWithItems:@[gesture.view] mode:UIPushBehaviorModeInstantaneous];
        pushBehavior.pushDirection = CGVectorMake((velocity.x / 10) , (velocity.y / 10));
        // some constant to limit the speed of the animation
        pushBehavior.magnitude = velocityMagnitude / 35.0;
        CGPoint finalPoint = [gesture locationInView:gesture.view.superview];
        CGPoint center = gesture.view.center;
        [pushBehavior setTargetOffsetFromCenter:UIOffsetMake(finalPoint.x - center.x, finalPoint.y - center.y) forItem:gesture.view];

        // when the view no longer intersects with its superview, go ahead and remove it

        typeof(self) __weak weakSelf = self;

        pushBehavior.action = ^{
            if (!CGRectIntersectsRect(gesture.view.superview.bounds, gesture.view.frame)) {
                [weakSelf.animator removeAllBehaviors];
                [gesture.view removeFromSuperview];

                [[[UIAlertView alloc] initWithTitle:nil message:@"View is gone!" delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil] show];
            }
        };
        [self.animator addBehavior:pushBehavior];

        // add a little gravity so it accelerates off the screen (in case user gesture was slow)

        UIGravityBehavior *gravity = [[UIGravityBehavior alloc] initWithItems:@[gesture.view]];
        gravity.magnitude = 0.7;
        [self.animator addBehavior:gravity];
    }
}