components/FlexibleHeader/src/MDCFlexibleHeaderContainerViewController.m

// Copyright 2015-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 "MDCFlexibleHeaderContainerViewController.h"

#import "MDCFlexibleHeaderView.h"
#import "MDCFlexibleHeaderViewController.h"

@implementation MDCFlexibleHeaderContainerViewController

- (instancetype)initWithContentViewController:(UIViewController *)contentViewController {
  self = [super initWithNibName:nil bundle:nil];
  if (self) {
    _headerViewController = [[MDCFlexibleHeaderViewController alloc] init];
    _headerViewController.inferTopSafeAreaInsetFromViewController = YES;
    [self addChildViewController:_headerViewController];

    self.contentViewController = contentViewController;
  }
  return self;
}

- (instancetype)initWithNibName:(__unused NSString *)nibNameOrNil
                         bundle:(__unused NSBundle *)nibBundleOrNil {
  return [self initWithContentViewController:nil];
}

- (instancetype)initWithCoder:(__unused NSCoder *)aDecoder {
  return [self initWithContentViewController:nil];
}

- (void)viewDidLoad {
  [super viewDidLoad];

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

  // Enforce the header's desire to fully cover the width of its parent view.
  CGRect frame = self.view.frame;
  frame.origin.x = 0;
  frame.size.width = self.view.bounds.size.width;
  self.headerViewController.view.frame = self.view.bounds;
  [self.view addSubview:self.headerViewController.view];
  [self.headerViewController didMoveToParentViewController:self];

  [self updateTopLayoutGuideBehavior];
}

- (void)viewWillLayoutSubviews {
  [super viewWillLayoutSubviews];

  if (!self.topLayoutGuideAdjustmentEnabled) {
    [self.headerViewController updateTopLayoutGuide];
  }
}

- (BOOL)prefersStatusBarHidden {
  return _headerViewController.prefersStatusBarHidden;
}

- (UIStatusBarStyle)preferredStatusBarStyle {
  return _headerViewController.preferredStatusBarStyle;
}

#pragma mark TraitCollection

- (void)traitCollectionDidChange:(UITraitCollection *)previousTraitCollection {
  [super traitCollectionDidChange:previousTraitCollection];

  if (self.traitCollectionDidChangeBlock) {
    self.traitCollectionDidChangeBlock(self, previousTraitCollection);
  }
}

#pragma mark - Public

- (void)setContentViewController:(UIViewController *)contentViewController {
  if (_contentViewController == contentViewController) {
    return;
  }

  // Teardown of the old controller

  [_contentViewController willMoveToParentViewController:nil];
  if ([_contentViewController isViewLoaded]) {
    [_contentViewController.view removeFromSuperview];
  }
  [_contentViewController removeFromParentViewController];

  // Setup of the new controller

  _contentViewController = contentViewController;

  if (contentViewController != nil) {
    [self addChildViewController:contentViewController];
    if ([self isViewLoaded]) {
      [self.view insertSubview:contentViewController.view
                  belowSubview:self.headerViewController.headerView];
      [contentViewController didMoveToParentViewController:self];
    }
  }

  [self updateTopLayoutGuideBehavior];
}

#pragma mark - Enabling top layout guide adjustment behavior

- (void)updateTopLayoutGuideBehavior {
  if (self.topLayoutGuideAdjustmentEnabled) {
    if ([self isViewLoaded]) {
      self.contentViewController.view.translatesAutoresizingMaskIntoConstraints = YES;
      self.contentViewController.view.autoresizingMask =
          (UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight);
      self.contentViewController.view.frame = self.view.bounds;
    }

    // The flexible header view controller, by default, will assume that it is a child view
    // controller of the content view controller and modify its parent view controller's
    // topLayoutGuide. With an App Bar container view controller, however, our flexible header's
    // parent is the app bar container view controller instead. There does not appear to be a way to
    // make two top layout guides constrain to one other
    // (e.g. self.topLayoutGuide == self.contentViewController.topLayoutGuide) so instead we must
    // tell the flexible header controller which view controller it should modify.
    self.headerViewController.topLayoutGuideViewController = self.contentViewController;

  } else {
    self.headerViewController.topLayoutGuideViewController = nil;
  }
}

- (void)setTopLayoutGuideAdjustmentEnabled:(BOOL)topLayoutGuideAdjustmentEnabled {
  if (_topLayoutGuideAdjustmentEnabled == topLayoutGuideAdjustmentEnabled) {
    return;
  }
  _topLayoutGuideAdjustmentEnabled = topLayoutGuideAdjustmentEnabled;

  [self updateTopLayoutGuideBehavior];
}

@end