iOS Tab的转场动画的一个问题

Question

1.如果我是正常速度切换Tab的时候，没有问题，如果我是快速（非常快，不然不会出现问题）的切换tab，就会出现空白页，也就是Tab里面的导航视图都不见，然后打断点，看了半天发现如果快速切换的时候 transitionContext.containerView没有了 也就是==nil了，而transitionContext.containerView是实现动画的容器

2.转场动画一般在- (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext{}方法里面进行

3.关键代码:

fromViewController.view.frame = fromFrame;
toViewController.view.frame = CGRectOffset(toFrame,
                            toFrame.size.width * offset.dx * -1,
                            toFrame.size.height * offset.dy * -1);
 transitionContext.containerView.backgroundColor = [UIColor redColor];
[transitionContext.containerView addSubview:toViewController.view];
NSTimeInterval transitionDuration = [self transitionDuration:transitionContext];
NSLog(@"+++++++++++%@",transitionContext.containerView);

[UIView animateWithDuration:transitionDuration animations:^{

    fromViewController.view.frame = CGRectOffset(fromFrame,
                                  fromFrame.size.width * offset.dx,
                                  fromFrame.size.height * offset.dy);
    toViewController.view.frame = toFrame;
    toViewController.view.backgroundColor = [UIColor blueColor];
} completion:^(BOOL finished)
{

[transitionContext completeTransition:![transitionContext transitionWasCancelled]];

 NSLog(@"===========%@",transitionContext.containerView);
    
}];  

4.如果有大神知道的，指导一二 谢谢