material-components_material-components-ios/components/AppBar/examples/supplemental/AppBarSampleViewController.m

// Copyright 2020-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 "AppBarSampleViewController.h"

#import "MaterialAppBar+Theming.h"

@implementation AppBarSampleViewController

- (void)dealloc {
  // Required for pre-iOS 11 devices because we've enabled observesTrackingScrollViewScrollEvents.
  self.appBarViewController.headerView.trackingScrollView = nil;
}

- (id)init {
  UICollectionViewFlowLayout *layout = [[UICollectionViewFlowLayout alloc] init];
  layout.minimumInteritemSpacing = 10;

  self = [super initWithCollectionViewLayout:layout];

  if (self) {
    self.title = @"Presented App Bar";

    _appBarViewController = [[MDCAppBarViewController alloc] init];

    // Behavioral flags.
    _appBarViewController.inferTopSafeAreaInsetFromViewController = YES;
    _appBarViewController.headerView.minMaxHeightIncludesSafeArea = NO;

    [self addChildViewController:_appBarViewController];
  }
  return self;
}

- (void)viewDidLoad {
  [super viewDidLoad];

  // Allows us to avoid forwarding events, but means we can't enable shift behaviors.
  self.appBarViewController.headerView.observesTrackingScrollViewScrollEvents = YES;
  [_appBarViewController applyPrimaryThemeWithScheme:self.containerScheme];

  // Need to update the status bar style after applying the theme.
  [self setNeedsStatusBarAppearanceUpdate];

  _appBarViewController.headerView.trackingScrollView = self.collectionView;

  [self.view addSubview:_appBarViewController.view];
  [_appBarViewController didMoveToParentViewController:self];

  [self.collectionView registerClass:[UICollectionViewCell class]
          forCellWithReuseIdentifier:@"Cell"];

  self.navigationItem.leftBarButtonItem =
      [[UIBarButtonItem alloc] initWithTitle:@"Dismiss"
                                       style:UIBarButtonItemStyleDone
                                      target:self
                                      action:@selector(dismiss)];
}

- (UIStatusBarStyle)preferredStatusBarStyle {
  return UIStatusBarStyleLightContent;
}

- (void)dismiss {
  [self.presentingViewController dismissViewControllerAnimated:YES completion:nil];
}

- (NSInteger)collectionView:(UICollectionView *)collectionView
     numberOfItemsInSection:(NSInteger)section {
  return 100;
}

- (CGSize)preferredContentSize {
  return CGSizeMake(300, 300);
}

- (__kindof UICollectionViewCell *)collectionView:(UICollectionView *)collectionView
                           cellForItemAtIndexPath:(NSIndexPath *)indexPath {
  UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"Cell"
                                                                         forIndexPath:indexPath];
  switch (indexPath.row % 3) {
    case 0:
      cell.backgroundColor = [UIColor colorWithWhite:(CGFloat)0.2 alpha:1];
      break;
    case 1:
      cell.backgroundColor = [UIColor colorWithWhite:(CGFloat)0.5 alpha:1];
      break;
    case 2:
      cell.backgroundColor = [UIColor colorWithWhite:(CGFloat)0.7 alpha:1];
      break;
    default:
      break;
  }

  return cell;
}

- (CGSize)collectionView:(UICollectionView *)collectionView
                    layout:(UICollectionViewLayout *)collectionViewLayout
    sizeForItemAtIndexPath:(NSIndexPath *)indexPath {
  CGRect collectionViewFrame = collectionView.frame;
  return CGSizeMake(collectionViewFrame.size.width / 2 - 14, 40);
}

@end