components/Dialogs/src/MDCDialogTransitionController.m

// Copyright 2016-present the Material Components for iOS authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#import "MDCDialogTransitionController.h"

#import "MDCDialogPresentationController.h"

@implementation MDCDialogTransitionController

static const NSTimeInterval MDCDialogTransitionDuration = 0.27;

#pragma mark - UIViewControllerAnimatedTransitioning

- (NSTimeInterval)transitionDuration:
    (__unused id<UIViewControllerContextTransitioning>)transitionContext {
  return MDCDialogTransitionDuration;
}

- (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext {
  // If a view in the transitionContext is nil, it likely hasn't been loaded by its ViewController
  // yet.  Ask for it directly to initiate a loadView on the ViewController.
  UIViewController *fromViewController =
      [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
  UIView *fromView = [transitionContext viewForKey:UITransitionContextFromViewKey];
  if (fromView == nil) {
    fromView = fromViewController.view;
  }

  UIViewController *toViewController =
      [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
  UIView *toView = [transitionContext viewForKey:UITransitionContextToViewKey];
  if (toView == nil) {
    toView = toViewController.view;
  }

  UIViewController *toPresentingViewController = toViewController.presentingViewController;
  BOOL presenting = (toPresentingViewController == fromViewController) ? YES : NO;

  UIViewController *animatingViewController = presenting ? toViewController : fromViewController;
  UIView *animatingView = presenting ? toView : fromView;

  UIView *containerView = transitionContext.containerView;

  if (presenting) {
    [containerView addSubview:toView];
  }

  CGFloat startingAlpha = presenting ? 0 : 1;
  CGFloat endingAlpha = presenting ? 1 : 0;

  animatingView.frame = [transitionContext finalFrameForViewController:animatingViewController];
  animatingView.alpha = startingAlpha;

  NSTimeInterval transitionDuration = [self transitionDuration:transitionContext];
  UIViewAnimationOptions options =
      UIViewAnimationOptionAllowUserInteraction | UIViewAnimationOptionBeginFromCurrentState;

  [UIView animateWithDuration:transitionDuration
      delay:0.0
      options:options
      animations:^{
        animatingView.alpha = endingAlpha;
      }
      completion:^(__unused BOOL finished) {
        // If we're dismissing, remove the presented view from the hierarchy
        if (!presenting) {
          [fromView removeFromSuperview];
        }

        // From ADC : UIViewControllerContextTransitioning
        // When you do create transition animations, always call the
        // completeTransition: from an appropriate completion block to let UIKit know
        // when all of your animations have finished.
        [transitionContext completeTransition:YES];
      }];
}

#pragma mark - UIViewControllerTransitioningDelegate

- (UIPresentationController *)
    presentationControllerForPresentedViewController:(UIViewController *)presented
                            presentingViewController:(UIViewController *)presenting
                                sourceViewController:(__unused UIViewController *)source {
  return [[MDCDialogPresentationController alloc] initWithPresentedViewController:presented
                                                         presentingViewController:presenting];
}

- (id<UIViewControllerAnimatedTransitioning>)
    animationControllerForPresentedController:(__unused UIViewController *)presented
                         presentingController:(__unused UIViewController *)presenting
                             sourceController:(__unused UIViewController *)source {
  return self;
}

- (id<UIViewControllerAnimatedTransitioning>)animationControllerForDismissedController:
    (__unused UIViewController *)dismissed {
  return self;
}

@end