• (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext {
  UIView *containerView = [transitionContext containerView];
  UIViewController *fromController = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
  UIViewController *toController = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
  UIView *toView = toController.view;
  // Enter
  if (toController.isBeingPresented) {
  _isEnter = YES;
  self.isTransitioning = YES;
  if ([self enter_configAnimateImageView]) {
  containerView.backgroundColor = [UIColor clearColor];
  [containerView addSubview:toView];
  [containerView addSubview:self.animateImageView];
  toView.alpha = 0;
  [self.imageBrowser setConnentHidden:YES];
  self.animateImageView.frame = CGRectMake(0, 0, 50, 50);
  self.animateImageView.center = containerView.center;
  [UIView animateWithDuration:[self transitionDuration:transitionContext] animations:^{
  toView.alpha = 1;
  self.animateImageView.frame = [self enterInFrame];
  } completion:^(BOOL finished) {
  [self completeTransition:transitionContext isEnter:YES];
  [self.animateImageView removeFromSuperview];
  }];
  } else {
  [containerView addSubview:toView];
  [self completeTransition:transitionContext isEnter:YES];
  }
  }

  // Out
  if (fromController.isBeingDismissed) {
  _isEnter = NO;
  self.isTransitioning = YES;
  UIView *fromAnimateView = [self.imageBrowser animatedView];
  CGRect toFrame = fromAnimateView.frame;
  if (fromAnimateView) {
  CGRect fromFrame = [fromAnimateView convertRect:fromAnimateView.frame toView:fromController.view];
  if (CGRectGetMidY(fromFrame) > fromController.view.center.y) {
  // 下移
  toFrame.origin.y = CGRectGetMaxY(fromController.view.frame);
  } else if (CGRectGetMidY(fromFrame) < fromController.view.center.y) {
  toFrame.origin.y = -CGRectGetHeight(fromFrame);
  } else {
  //漸變
  toFrame = CGRectZero;
  }
  [UIView animateWithDuration:[self transitionDuration:transitionContext] animations:^{
  if (CGRectEqualToRect(toFrame, CGRectZero)) {
  fromController.view.alpha = 0;
  } else {
  fromAnimateView.frame = toFrame;
  }
  fromController.view.backgroundColor = [fromController.view.backgroundColor colorWithAlphaComponent:0];

        } completion:^(BOOL finished) {
            [self completeTransition:transitionContext isEnter:NO];
        }];
    } else {
        [self completeTransition:transitionContext isEnter:NO];
    }
  

  }
  }

• (void)completeTransition:(nullable id <UIViewControllerContextTransitioning>)transitionContext isEnter:(BOOL)isEnter {
  [transitionContext completeTransition:!transitionContext.transitionWasCancelled];
  self.isTransitioning = NO;
  if (isEnter) {
  [self.imageBrowser setConnentHidden:NO];
  }
  }

pragma mark - private

• (BOOL)enter_configAnimateImageView {
  WKTopicBrowserModel *model= self.imageBrowser.currentModel;
  if (!model) return NO;

  CGSize imagesize;

  FLAnimatedImage *image = [[FLAnimatedImage alloc] initWithAnimatedGIFData:model.posterImageData];
  if (image) {
  self.animateImageView.animatedImage = image;
  imagesize = image.size;
  } else {
  self.animateImageView.image = [UIImage imageWithData:model.posterImageData];
  imagesize = self.animateImageView.image.size;
  }
  self.animateImageView.frame = CGRectZero;

  return YES;
  }

• (CGRect)enterInFrame {
  CGSize imagesize;
  if (self.animateImageView.animatedImage) {
  imagesize = self.animateImageView.animatedImage.size;
  } else {
  imagesize = self.animateImageView.image.size;
  }
  CGSize screenSize = [[UIScreen mainScreen] bounds].size;
  CGFloat maxScale = MIN(screenSize.width/imagesize.width, screenSize.height/imagesize.height);

    imagesize.width = imagesize.width * maxScale;
    imagesize.height = imagesize.height * maxScale;
  

  return CGRectMake((screenSize.width-imagesize.width)/2, (screenSize.height-imagesize.height)/2, imagesize.width, imagesize.height);
  }

pragma mark - getter

• (FLAnimatedImageView *)animateImageView {
  if (!_animateImageView) {
  _animateImageView = [FLAnimatedImageView new];
  _animateImageView.contentMode = UIViewContentModeScaleAspectFit;
  }
  return _animateImageView;
  }