/*

 Copyright (C) 2016 Apple Inc. All Rights Reserved.

 See LICENSE.txt for this sample’s licensing information

 Abstract:

 A transition animator that performs a cross dissolve transition between

  two view controllers.

 */

#import "AAPLCrossDissolveTransitionAnimator.h"

@implementation AAPLCrossDissolveTransitionAnimator

//| ----------------------------------------------------------------------------

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

{

    return 0.35;

}

//| ----------------------------------------------------------------------------

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

{

    UIViewController *fromViewController = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];

    UIViewController *toViewController = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];

    UIView *containerView = transitionContext.containerView;

    // For a Presentation:

    //      fromView = The presenting view.

    //      toView   = The presented view.

    // For a Dismissal:

    //      fromView = The presented view.

    //      toView   = The presenting view.

    UIView *fromView;

    UIView *toView;

    // In iOS 8, the viewForKey: method was introduced to get views that the

    // animator manipulates.  This method should be preferred over accessing

    // the view of the fromViewController/toViewController directly.

    // It may return nil whenever the animator should not touch the view

    // (based on the presentation style of the incoming view controller).

    // It may also return a different view for the animator to animate.

    //

    // Imagine that you are implementing a presentation similar to form sheet.

    // In this case you would want to add some shadow or decoration around the

    // presented view controller's view. The animator will animate the

    // decoration view instead and the presented view controller's view will

    // be a child of the decoration view.

    if ([transitionContext respondsToSelector:@selector(viewForKey:)]) {

        fromView = [transitionContext viewForKey:UITransitionContextFromViewKey];

        toView = [transitionContext viewForKey:UITransitionContextToViewKey];

    } else {

        fromView = fromViewController.view;

        toView = toViewController.view;

    }

    fromView.frame = [transitionContext initialFrameForViewController:fromViewController];

    toView.frame = [transitionContext finalFrameForViewController:toViewController];

    fromView.alpha = 1.0f;

    toView.alpha = 0.0f;

    // We are responsible for adding the incoming view to the containerView

    // for the presentation/dismissal.

    [containerView addSubview:toView];

    NSTimeInterval transitionDuration = [self transitionDuration:transitionContext];

    [UIView animateWithDuration:transitionDuration animations:^{

        fromView.alpha = 0.0f;

        toView.alpha = 1.0;

    } completion:^(BOOL finished) {

        // When we complete, tell the transition context

        // passing along the BOOL that indicates whether the transition

        // finished or not.

        BOOL wasCancelled = [transitionContext transitionWasCancelled];

        [transitionContext completeTransition:!wasCancelled];

    }];

}

@end