title: "From View Controller" disappears using UIViewControllerContextTransitioning
body: <p>I got one problem and i have described it below.</p>
  
  <p>I am using <code>UIViewControllerContextTransitioning</code> for custom transitions.</p>
  
  <p>I have 2 view controllers, first view controller and second view controller.</p>
  
  <p>Now I want to add second view controller on first view controller with an animation. I have achieved it, now the second view controller is transparent, so we can see first view controller below second view controller.</p>
  
  <p>But I am not able to see first view controller, and I can see only black screen below second view controller.</p>
  
  <pre><code>-(void)animateTransition:(id&lt;UIViewControllerContextTransitioning&gt;)transitionContext{
      self.transitionContext = transitionContext;
      if(self.isPresenting){
          [self executePresentationAnimation:transitionContext];
      }
      else{
         [self executeDismissalAnimation:transitionContext];
      }
    }
  
  -(void)executePresentationAnimation:(id&lt;UIViewControllerContextTransitioning&gt;)transitionContext{
       UIView* inView = [transitionContext containerView];
       UIViewController* toViewController = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
  
       UIViewController* fromViewController = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
  
       CGRect offScreenFrame = inView.frame;
       offScreenFrame.origin.y = inView.frame.size.height;
       toViewController.view.frame = offScreenFrame;
  
      toViewController.view.backgroundColor = [UIColor clearColor];
      fromViewController.view.backgroundColor = [UIColor clearColor];
      inView.backgroundColor = [UIColor  clearColor];
      [inView insertSubview:toViewController.view aboveSubview:fromViewController.view];
       // [inView addSubview:toViewController.view];
      CFTimeInterval duration = self.presentationDuration;
      CFTimeInterval halfDuration = duration/2;
  
      CATransform3D t1 = [self firstTransform];
      CATransform3D t2 = [self secondTransformWithView:fromViewController.view];
  
      [UIView animateKeyframesWithDuration:halfDuration delay:0.0 options:UIViewKeyframeAnimationOptionCalculationModeLinear animations:^{
  
      [UIView addKeyframeWithRelativeStartTime:0.0f relativeDuration:0.5f animations:^{
          fromViewController.view.layer.transform = t1;
      }];
  
      [UIView addKeyframeWithRelativeStartTime:0.5f relativeDuration:0.5f animations:^{
          fromViewController.view.layer.transform = t2;
      }];
      } completion:^(BOOL finished) {
      }];
  
  
      [UIView animateWithDuration:duration delay:(halfDuration - (0.3*halfDuration)) usingSpringWithDamping:0.7f initialSpringVelocity:6.0f options:UIViewAnimationOptionCurveEaseIn animations:^{
          toViewController.view.frame = inView.frame;
      } completion:^(BOOL finished) {
          [self.transitionContext completeTransition:YES];
      }];
  }
  </code></pre>
  
  <p>When <code>[self.transitionContext completeTransition:YES];</code> called, suddenly the first view controller disappears and black screen displays below second view controller.</p>
  
  <p>Does any one have idea ?
  Thanks.</p>