Custom Transitions Between VCs

BouncyTransition.h

#import <Foundation/Foundation.h>

@interface BouncyTransition : NSObject <UIViewControllerAnimatedTransitioning>

@end

BouncyTransition.m

@implementation BouncyTransition

- (NSTimeInterval)transitionDuration:(id<UIViewContollerContextTransitioning>)transitionContext
{
  return 1.0f;
}

- (void)animateTransition:(id<UIViewContollerContextTransitioning>)transitionContext
{
  // 1. Insert modal view into transition view hierarchy
  // First get the to and from VCs
  UIViewController *toVC = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
  UIViewController *fromVC = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
  
  [[transitionContext containerView] addSubview:toVC.view];
  
  // 2. Set starting position of modal view
  // get initial frame of fromVC:
  CGRect fullFrame = [transitionContext initialFrameForViewController:fromVC];
  CGFloat height = CGRectGetHeight(fullFrame);
  toView.view.frame = CGRectMake(
        fullFrame.origin.x + 20,
        height + 16 + 20,
        CGRectGetWidth(fullFrame) - 40,
        height -40
      );
  
  // 3. Animate modal into position using UIView animations
  
  [UIView animateWithDuration:[self transitionDuration:transitionContext];
      delay:0.0f
      usingSpringWithDamping:0.5f
      initialSpringVelocity:0.6f
      options:UIViewAnimationOptionCurveEaseInOut
      animations:^{
          toVC.view.frame = CGRectMake(
                20,
                20,
                CGRectGetWidth(fullFrame) -40,
                height-40);
      }
  // 4. Complete the transition or else the UI will be frozen
      completion:^(BOOL finished) {
        [transitionContext completeTransition:YES];
      }
  ];
  
  
  
}

RootVC.h

@interface RootVC : UIViewController <UIViewControllerTransitioningDelegate>
// That'll make it so you can implement the - (id <UIViewControllerAnimatedTransitioning>)animationControllerForPresentedController... method.

RootVC.m

import "BouncyTransition.h"

- (void)loginButtonTapped:(id)sender
{
  LoginVC *loginVC = [[LoginVC alloc] init];
  
  loginVC.modalPresentationStyle = UIModalPresentationCustom;
 
  loginVC.transitioningDelegate = self;
  
  [self presentViewController:loginVC
    animated:YES
    completion:NIL];
}

- (id <UIViewControllerAnimatedTransitioning>)animationControllerForPresentedController:(UIViewController *)presented
        presentingViewController:(UIViewController*)presenting
        sourceController:(UIViewController *)source
{
  BouncyTransition *transition = [[BouncyTransition alloc] init];
  return transition;
}