components/BottomSheet/src/MDCBottomSheetTransitionController.m

/*
 Copyright 2017-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 "MDCBottomSheetTransitionController.h"

#import "MDCBottomSheetPresentationController.h"

static const NSTimeInterval MDCBottomSheetTransitionDuration = 0.25;

@implementation MDCBottomSheetTransitionController

#pragma mark - UIViewControllerTransitioningDelegate

- (UIPresentationController *)
    presentationControllerForPresentedViewController:(UIViewController *)presented
                            presentingViewController:(UIViewController *)presenting
                                sourceViewController:(__unused UIViewController *)source {
  MDCBottomSheetPresentationController *presentationController =
      [[MDCBottomSheetPresentationController alloc] initWithPresentedViewController:presented
                                                           presentingViewController:presenting];
  presentationController.trackingScrollView = self.trackingScrollView;
  presentationController.dismissOnBackgroundTap = self.dismissOnBackgroundTap;
  return presentationController;
}

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

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

#pragma mark - UIViewControllerAnimatedTransitioning

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

- (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];
  }

  CGRect onscreenFrame = [self frameOfPresentedViewController:animatingViewController
                                              inContainerView:containerView];
  CGRect offscreenFrame = CGRectOffset(onscreenFrame, 0, containerView.frame.size.height);

  CGRect initialFrame = presenting ? offscreenFrame : onscreenFrame;
  CGRect finalFrame = presenting ? onscreenFrame : offscreenFrame;

  animatingView.frame = initialFrame;

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

  [UIView animateWithDuration:transitionDuration
                        delay:0.0
                      options:options
                   animations:^{
                     animatingView.frame = finalFrame;
                   }
                   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];
                   }];
}

- (CGRect)frameOfPresentedViewController:(UIViewController *)presentedViewController
                         inContainerView:(UIView *)containerView {
  CGSize containerSize = containerView.frame.size;
  CGSize preferredSize = presentedViewController.preferredContentSize;

  if (preferredSize.width > 0 && preferredSize.width < containerSize.width) {
    CGFloat width = preferredSize.width;
    CGFloat leftPad = (containerSize.width - width) / 2;
    return CGRectMake(leftPad, 0, width, containerSize.height);
  } else {
    return containerView.frame;
  }
}

@end