ios – 在视图控制器转换中获取子视图的最终帧 - iOS

我希望在从视图控制器A到视图控制器B的过渡中,来自A的按钮向上移动,使其在视图控制器B中的最终位置结束.

这是我的animateTransition：方法：

- (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext{    UIViewController *fromViewController = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];    UIViewController *toViewController = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];    UIView *containerView = [transitionContext containerView];    [containerView insertSubview:toViewController.view belowSubview:fromViewController.view];    UIButton *fromButton = (UIButton *)[containerView viewWithTag:1];    UIButton *toButton = (UIButton *)[containerView viewWithTag:2];    toButton.hidden = YES;    [UIView animateWithDuration:[self transitionDuration:transitionContext] animations:^{        fromButton.center = toButton.center;    } completion:^(BOOL finished) {        toButton.hidden = NO;        [transitionContext completeTransition:![transitionContext transitionWasCancelled]];    }];}

我看到的问题是toButton.center不是正确的位置.就像AutoLayout约束还没有被应用(我得到与IB中相同的框架矩形).这导致在转换完成后按钮不会在正确的位置结束.

哪里出错？如何从呈现的视图控制器中获取正确的子视图最终帧？如果由于视图控制器B尚未出现而无法实现,那么我如何设置子视图动画才能实现此效果？