/*

 Copyright (C) 2018 Apple Inc. All Rights Reserved.

 See LICENSE.txt for this sample’s licensing information

 Abstract:

 Animator between the two view controllers by performing a simple cross-fade.

 */

#import "CrossfadeAnimationController.h"

@implementation CrossfadeAnimationController

- (id)init

{

    if (self = [super init])

    {

        _duration = 1.0f;   // Default duration.

    }

    return self;

}

- (NSTimeInterval)transitionDuration:(id<UIViewControllerContextTransitioning>)transitionContext

{

    return self.duration;

}

- (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext

{

    UIViewController *fromVC = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];

    UIViewController *toVC = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];

    UIView *toView = toVC.view;

    UIView *fromView = fromVC.view;

    [self animateTransition:transitionContext fromVC:fromVC toVC:toVC fromView:fromView toView:toView];

}

- (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext fromVC:(UIViewController *)fromVC toVC:(UIViewController *)toVC fromView:(UIView *)fromView toView:(UIView *)toView

{

    // Add the toView to the container.

    UIView *containerView = [transitionContext containerView];

    [containerView addSubview:toView];

    [containerView sendSubviewToBack:toView];

    // Do the cross-fade transition.

    NSTimeInterval duration = [self transitionDuration:transitionContext];

    [UIView animateWithDuration:duration animations:^{

        fromView.alpha = 0.0;

    } completion:^(BOOL finished) {

        if ([transitionContext transitionWasCancelled])

        {

            fromView.alpha = 1.0;

        }

        else

        {

            // Reset from- view to its original state.

            [fromView removeFromSuperview];

            fromView.alpha = 1.0;

        }

        [transitionContext completeTransition:![transitionContext transitionWasCancelled]];

    }];

}

@end