components/AppBar/src/MDCAppBarViewController.m - external/github.com/material-components/material-components-ios.git - Git at Google

 // 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 "MDCAppBarViewController.h"

 #import "MDCAppBarContainerViewController.h"

 #import "private/MaterialAppBarStrings.h"
 #import "private/MaterialAppBarStrings_table.h"
 #import "MDCAppBarViewControllerAccessibilityPerformEscapeDelegate.h"
 #import "MaterialFlexibleHeader.h"
 #import "MaterialHeaderStackView.h"
 #import "MaterialNavigationBar.h"
 #import "MaterialShadowElevations.h"
 #import "MaterialShadowLayer.h"
 #import "MaterialIcons+ic_arrow_back.h"
 #import "MaterialUIMetrics.h"
 #import <MDFInternationalization/MDFInternationalization.h>

 static NSString *const kBarStackKey = @"barStack";

 // The Bundle for string resources.
 static NSString *const kMaterialAppBarBundle = @"MaterialAppBar.bundle";

 @implementation MDCAppBarViewController {
   NSLayoutConstraint *_verticalConstraint;
   NSLayoutConstraint *_topSafeAreaConstraint;
 }

 - (instancetype)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil {
   self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
   if (self) {
     [self MDCAppBarViewController_commonInit];
   }
   return self;
 }

 - (instancetype)initWithCoder:(NSCoder *)aDecoder {
   self = [super initWithCoder:aDecoder];
   if (self) {
     [self MDCAppBarViewController_commonInit];
   }
   return self;
 }

 - (void)MDCAppBarViewController_commonInit {
   // Shadow layer
   __weak MDCAppBarViewController *weakSelf = self;
   MDCFlexibleHeaderShadowIntensityChangeBlock intensityBlock =
       ^(CALayer *_Nonnull shadowLayer, CGFloat intensity) {
         CGFloat elevation = MDCShadowElevationAppBar * intensity;
         weakSelf.headerView.elevation = elevation;
         [(MDCShadowLayer *)shadowLayer setElevation:elevation];
       };
   [self.headerView setShadowLayer:[MDCShadowLayer layer] intensityDidChangeBlock:intensityBlock];

   [self.headerView forwardTouchEventsForView:self.headerStackView];
   [self.headerView forwardTouchEventsForView:self.navigationBar];

   self.headerStackView.translatesAutoresizingMaskIntoConstraints = NO;
   self.headerStackView.topBar = self.navigationBar;
 }

 #pragma mark - Properties

 - (MDCHeaderStackView *)headerStackView {
   // Removed call to loadView here as we should never be calling it manually.
   // It previously replaced loadViewIfNeeded call that is only iOS 9.0+ to
   // make backwards compatible.
   // Underlying issue is you need view loaded before accessing. Below change will accomplish that
   // by calling for view.bounds initializing the stack view
   if (!_headerStackView) {
     _headerStackView = [[MDCHeaderStackView alloc] initWithFrame:CGRectZero];
   }
   return _headerStackView;
 }

 - (MDCNavigationBar *)navigationBar {
   if (!_navigationBar) {
     _navigationBar = [[MDCNavigationBar alloc] init];
   }
   return _navigationBar;
 }

 - (UIBarButtonItem *)backButtonItem {
   UIViewController *parent = self.parentViewController;
   UINavigationController *navigationController = parent.navigationController;

   NSArray<UIViewController *> *viewControllerStack = navigationController.viewControllers;

   // This will be zero if there is no navigation controller, so a view controller which is not
   // inside a navigation controller will be treated the same as a view controller at the root of a
   // navigation controller
   NSUInteger index = [viewControllerStack indexOfObject:parent];

   UIViewController *iterator = parent;

   // In complex cases it might actually be a parent of @c fhvParent which is on the nav stack.
   while (index == NSNotFound && iterator && ![iterator isEqual:navigationController]) {
     iterator = iterator.parentViewController;
     index = [viewControllerStack indexOfObject:iterator];
   }

   if (index == NSNotFound) {
     NSCAssert(NO, @"View controller not present in its own navigation controller.");
     // This is not something which should ever happen, but just in case.
     return nil;
   }
   if (index == 0) {
     // The view controller is at the root of a navigation stack (or not in one).
     return nil;
   }
   UIViewController *previousViewControler = navigationController.viewControllers[index - 1];
   if ([previousViewControler isKindOfClass:[MDCAppBarContainerViewController class]]) {
     // Special case: if the previous view controller is a container controller, use its content
     // view controller.
     MDCAppBarContainerViewController *chvc =
         (MDCAppBarContainerViewController *)previousViewControler;
     previousViewControler = chvc.contentViewController;
   }
   UIBarButtonItem *backBarButtonItem = previousViewControler.navigationItem.backBarButtonItem;
   if (!backBarButtonItem) {
     UIImage *backButtonImage = [MDCIcons imageFor_ic_arrow_back];
     backButtonImage = [backButtonImage imageWithRenderingMode:UIImageRenderingModeAlwaysTemplate];
     if (self.navigationBar.mdf_effectiveUserInterfaceLayoutDirection ==
         UIUserInterfaceLayoutDirectionRightToLeft) {
       backButtonImage = [backButtonImage mdf_imageWithHorizontallyFlippedOrientation];
     }
     backBarButtonItem = [[UIBarButtonItem alloc] initWithImage:backButtonImage
                                                          style:UIBarButtonItemStyleDone
                                                         target:self
                                                         action:@selector(didTapBackButton:)];
   }
   backBarButtonItem.accessibilityIdentifier = @"back_bar_button";
   NSString *key = kMaterialAppBarStringTable[kStr_MaterialAppBarBackButtonAccessibilityLabel];
   backBarButtonItem.accessibilityLabel = NSLocalizedStringFromTableInBundle(
       key, kMaterialAppBarStringsTableName, [[self class] bundle], @"Back");
   return backBarButtonItem;
 }

 - (void)setShouldAdjustHeightBasedOnHeaderStackView:(BOOL)shouldAdjustHeightBasedOnHeaderStackView {
   _shouldAdjustHeightBasedOnHeaderStackView = shouldAdjustHeightBasedOnHeaderStackView;
   if (shouldAdjustHeightBasedOnHeaderStackView) {
     self.headerView.minMaxHeightIncludesSafeArea = NO;
     [self adjustHeightBasedOnHeaderStackView];
   }
 }

 - (void)setInferTopSafeAreaInsetFromViewController:(BOOL)inferTopSafeAreaInsetFromViewController {
   [super setInferTopSafeAreaInsetFromViewController:inferTopSafeAreaInsetFromViewController];

   if (inferTopSafeAreaInsetFromViewController) {
     self.topLayoutGuideAdjustmentEnabled = YES;
   }

   _verticalConstraint.active = !self.inferTopSafeAreaInsetFromViewController;
   _topSafeAreaConstraint.active = self.inferTopSafeAreaInsetFromViewController;
 }

 - (void)setHeaderStackViewOffset:(CGFloat)headerStackViewOffset {
   _headerStackViewOffset = headerStackViewOffset;
   _verticalConstraint.constant = [self verticalContraintLength];
   _topSafeAreaConstraint.constant = [self topSafeAreaContraintLength];
 }

 #pragma mark - Resource bundle

 + (NSBundle *)bundle {
   static NSBundle *bundle = nil;
   static dispatch_once_t onceToken;
   dispatch_once(&onceToken, ^{
     bundle = [NSBundle bundleWithPath:[self bundlePathWithName:kMaterialAppBarBundle]];
   });

   return bundle;
 }

 + (NSString *)bundlePathWithName:(NSString *)bundleName {
   // In iOS 8+, we could be included by way of a dynamic framework, and our resource bundles may
   // not be in the main .app bundle, but rather in a nested framework, so figure out where we live
   // and use that as the search location.
   NSBundle *bundle = [NSBundle bundleForClass:[MDCAppBar class]];
   NSString *resourcePath = [(nil == bundle ? [NSBundle mainBundle] : bundle) resourcePath];
   return [resourcePath stringByAppendingPathComponent:bundleName];
 }

 #pragma mark - UIViewController Overrides

 - (void)viewDidLoad {
   [super viewDidLoad];

   [self.view addSubview:self.headerStackView];

   // Bar stack expands vertically, but has a margin above it for the status bar.
   NSArray<NSLayoutConstraint *> *horizontalConstraints = [NSLayoutConstraint
       constraintsWithVisualFormat:[NSString stringWithFormat:@"H:|[%@]|", kBarStackKey]
                           options:0
                           metrics:nil
                             views:@{kBarStackKey : self.headerStackView}];
   [self.view addConstraints:horizontalConstraints];

   CGFloat topMargin = [self verticalContraintLength];
   _verticalConstraint = [NSLayoutConstraint constraintWithItem:self.headerStackView
                                                      attribute:NSLayoutAttributeTop
                                                      relatedBy:NSLayoutRelationEqual
                                                         toItem:self.view
                                                      attribute:NSLayoutAttributeTop
                                                     multiplier:1
                                                       constant:topMargin];
   _verticalConstraint.active = !self.inferTopSafeAreaInsetFromViewController;

   _topSafeAreaConstraint =
       [NSLayoutConstraint constraintWithItem:self.headerStackView
                                    attribute:NSLayoutAttributeTop
                                    relatedBy:NSLayoutRelationEqual
                                       toItem:self.headerView.topSafeAreaGuide
                                    attribute:NSLayoutAttributeBottom
                                   multiplier:1
                                     constant:[self topSafeAreaContraintLength]];
   _topSafeAreaConstraint.active = self.inferTopSafeAreaInsetFromViewController;

   [NSLayoutConstraint constraintWithItem:self.headerStackView
                                attribute:NSLayoutAttributeBottom
                                relatedBy:NSLayoutRelationEqual
                                   toItem:self.view
                                attribute:NSLayoutAttributeBottom
                               multiplier:1
                                 constant:0]
       .active = YES;
 }

 - (void)viewWillAppear:(BOOL)animated {
   [super viewWillAppear:animated];

   UIBarButtonItem *backBarButtonItem = [self backButtonItem];
   if (backBarButtonItem && !self.navigationBar.backItem) {
     self.navigationBar.backItem = backBarButtonItem;
   }
 }

 - (void)viewWillLayoutSubviews {
   [super viewWillLayoutSubviews];

   if (@available(iOS 11.0, *)) {
     // We only update the top inset on iOS 11 because previously we were not adjusting the header
     // height to make it smaller when the status bar is hidden.
     _verticalConstraint.constant = [self verticalContraintLength];
   }

   if (self.shouldAdjustHeightBasedOnHeaderStackView) {
     [self adjustHeightBasedOnHeaderStackView];
   }
 }

 - (void)didMoveToParentViewController:(UIViewController *)parent {
   [super didMoveToParentViewController:parent];

   [self.navigationBar observeNavigationItem:parent.navigationItem];

   CGRect frame = self.view.frame;
   frame.size.width = CGRectGetWidth(parent.view.bounds);
   self.view.frame = frame;
 }

 #pragma mark - UIAccessibility

 - (BOOL)accessibilityPerformEscape {
   if (self.accessibilityPerformEscapeDelegate) {
     return [self.accessibilityPerformEscapeDelegate
         appBarViewControllerAccessibilityPerformEscape:self];
   }

   // Fall-back behavior.
   [self dismissSelf];
   return YES;
 }

 #pragma mark User actions

 - (void)didTapBackButton:(__unused id)sender {
   [self dismissSelf];
 }

 - (void)dismissSelf {
   UIViewController *pvc = self.parentViewController;
   if (pvc.navigationController && pvc.navigationController.viewControllers.count > 1) {
     [pvc.navigationController popViewControllerAnimated:YES];
   } else {
     [pvc dismissViewControllerAnimated:YES completion:nil];
   }
 }

 #pragma mark - Private

 - (CGFloat)verticalContraintLength {
   return MDCDeviceTopSafeAreaInset() + _headerStackViewOffset;
 }

 - (CGFloat)topSafeAreaContraintLength {
   return _headerStackViewOffset;
 }

 - (void)adjustHeightBasedOnHeaderStackView {
   CGFloat heightSum = 0;
   heightSum += [self.headerStackView.topBar sizeThatFits:self.view.bounds.size].height;
   heightSum += [self.headerStackView.bottomBar sizeThatFits:self.view.bounds.size].height;
   heightSum += _headerStackViewOffset;
   self.headerView.minimumHeight = heightSum;
   self.headerView.maximumHeight = heightSum;
 }

 @end

 #pragma mark - To be deprecated

 @implementation MDCAppBar

 - (instancetype)init {
   self = [super init];
   if (self) {
     _appBarViewController = [[MDCAppBarViewController alloc] init];
   }
   return self;
 }

 - (MDCFlexibleHeaderViewController *)headerViewController {
   return self.appBarViewController;
 }

 - (MDCHeaderStackView *)headerStackView {
   return self.appBarViewController.headerStackView;
 }

 - (MDCNavigationBar *)navigationBar {
   return self.appBarViewController.navigationBar;
 }

 - (void)addSubviewsToParent {
   MDCAppBarViewController *abvc = self.appBarViewController;
   NSAssert(abvc.parentViewController,
            @"appBarViewController does not have a parentViewController. "
            @"Use [self addChildViewController:appBar.appBarViewController]. "
            @"This warning only appears in DEBUG builds");
   if (abvc.view.superview == abvc.parentViewController.view) {
     return;
   }

   // Enforce the header's desire to fully cover the width of its parent view.
   CGRect frame = abvc.view.frame;
   frame.origin.x = 0;
   frame.size.width = abvc.parentViewController.view.bounds.size.width;
   abvc.view.frame = frame;

   [abvc.parentViewController.view addSubview:abvc.view];
   [abvc didMoveToParentViewController:abvc.parentViewController];
 }

 - (void)setInferTopSafeAreaInsetFromViewController:(BOOL)inferTopSafeAreaInsetFromViewController {
   self.appBarViewController.inferTopSafeAreaInsetFromViewController =
       inferTopSafeAreaInsetFromViewController;
 }

 - (BOOL)inferTopSafeAreaInsetFromViewController {
   return self.appBarViewController.inferTopSafeAreaInsetFromViewController;
 }

 @end
	// 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 "MDCAppBarViewController.h"

	#import "MDCAppBarContainerViewController.h"

	#import "private/MaterialAppBarStrings.h"
	#import "private/MaterialAppBarStrings_table.h"
	#import "MDCAppBarViewControllerAccessibilityPerformEscapeDelegate.h"
	#import "MaterialFlexibleHeader.h"
	#import "MaterialHeaderStackView.h"
	#import "MaterialNavigationBar.h"
	#import "MaterialShadowElevations.h"
	#import "MaterialShadowLayer.h"
	#import "MaterialIcons+ic_arrow_back.h"
	#import "MaterialUIMetrics.h"
	#import <MDFInternationalization/MDFInternationalization.h>

	static NSString *const kBarStackKey = @"barStack";

	// The Bundle for string resources.
	static NSString *const kMaterialAppBarBundle = @"MaterialAppBar.bundle";

	@implementation MDCAppBarViewController {
	NSLayoutConstraint *_verticalConstraint;
	NSLayoutConstraint *_topSafeAreaConstraint;
	}

	- (instancetype)initWithNibName:(NSString )nibNameOrNil bundle:(NSBundle )nibBundleOrNil {
	self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
	if (self) {
	[self MDCAppBarViewController_commonInit];
	}
	return self;
	}

	- (instancetype)initWithCoder:(NSCoder *)aDecoder {
	self = [super initWithCoder:aDecoder];
	if (self) {
	[self MDCAppBarViewController_commonInit];
	}
	return self;
	}

	- (void)MDCAppBarViewController_commonInit {
	// Shadow layer
	__weak MDCAppBarViewController *weakSelf = self;
	MDCFlexibleHeaderShadowIntensityChangeBlock intensityBlock =
	^(CALayer *_Nonnull shadowLayer, CGFloat intensity) {
	CGFloat elevation = MDCShadowElevationAppBar * intensity;
	weakSelf.headerView.elevation = elevation;
	[(MDCShadowLayer *)shadowLayer setElevation:elevation];
	};
	[self.headerView setShadowLayer:[MDCShadowLayer layer] intensityDidChangeBlock:intensityBlock];

	[self.headerView forwardTouchEventsForView:self.headerStackView];
	[self.headerView forwardTouchEventsForView:self.navigationBar];

	self.headerStackView.translatesAutoresizingMaskIntoConstraints = NO;
	self.headerStackView.topBar = self.navigationBar;
	}

	#pragma mark - Properties

	- (MDCHeaderStackView *)headerStackView {
	// Removed call to loadView here as we should never be calling it manually.
	// It previously replaced loadViewIfNeeded call that is only iOS 9.0+ to
	// make backwards compatible.
	// Underlying issue is you need view loaded before accessing. Below change will accomplish that
	// by calling for view.bounds initializing the stack view
	if (!_headerStackView) {
	_headerStackView = [[MDCHeaderStackView alloc] initWithFrame:CGRectZero];
	}
	return _headerStackView;
	}

	- (MDCNavigationBar *)navigationBar {
	if (!_navigationBar) {
	_navigationBar = [[MDCNavigationBar alloc] init];
	}
	return _navigationBar;
	}

	- (UIBarButtonItem *)backButtonItem {
	UIViewController *parent = self.parentViewController;
	UINavigationController *navigationController = parent.navigationController;

	NSArray<UIViewController > viewControllerStack = navigationController.viewControllers;

	// This will be zero if there is no navigation controller, so a view controller which is not
	// inside a navigation controller will be treated the same as a view controller at the root of a
	// navigation controller
	NSUInteger index = [viewControllerStack indexOfObject:parent];

	UIViewController *iterator = parent;

	// In complex cases it might actually be a parent of @c fhvParent which is on the nav stack.
	while (index == NSNotFound && iterator && ![iterator isEqual:navigationController]) {
	iterator = iterator.parentViewController;
	index = [viewControllerStack indexOfObject:iterator];
	}

	if (index == NSNotFound) {
	NSCAssert(NO, @"View controller not present in its own navigation controller.");
	// This is not something which should ever happen, but just in case.
	return nil;
	}
	if (index == 0) {
	// The view controller is at the root of a navigation stack (or not in one).
	return nil;
	}
	UIViewController *previousViewControler = navigationController.viewControllers[index - 1];
	if ([previousViewControler isKindOfClass:[MDCAppBarContainerViewController class]]) {
	// Special case: if the previous view controller is a container controller, use its content
	// view controller.
	MDCAppBarContainerViewController *chvc =
	(MDCAppBarContainerViewController *)previousViewControler;
	previousViewControler = chvc.contentViewController;
	}
	UIBarButtonItem *backBarButtonItem = previousViewControler.navigationItem.backBarButtonItem;
	if (!backBarButtonItem) {
	UIImage *backButtonImage = [MDCIcons imageFor_ic_arrow_back];
	backButtonImage = [backButtonImage imageWithRenderingMode:UIImageRenderingModeAlwaysTemplate];
	if (self.navigationBar.mdf_effectiveUserInterfaceLayoutDirection ==
	UIUserInterfaceLayoutDirectionRightToLeft) {
	backButtonImage = [backButtonImage mdf_imageWithHorizontallyFlippedOrientation];
	}
	backBarButtonItem = [[UIBarButtonItem alloc] initWithImage:backButtonImage
	style:UIBarButtonItemStyleDone
	target:self
	action:@selector(didTapBackButton:)];
	}
	backBarButtonItem.accessibilityIdentifier = @"back_bar_button";
	NSString *key = kMaterialAppBarStringTable[kStr_MaterialAppBarBackButtonAccessibilityLabel];
	backBarButtonItem.accessibilityLabel = NSLocalizedStringFromTableInBundle(
	key, kMaterialAppBarStringsTableName, [[self class] bundle], @"Back");
	return backBarButtonItem;
	}

	- (void)setShouldAdjustHeightBasedOnHeaderStackView:(BOOL)shouldAdjustHeightBasedOnHeaderStackView {
	_shouldAdjustHeightBasedOnHeaderStackView = shouldAdjustHeightBasedOnHeaderStackView;
	if (shouldAdjustHeightBasedOnHeaderStackView) {
	self.headerView.minMaxHeightIncludesSafeArea = NO;
	[self adjustHeightBasedOnHeaderStackView];
	}
	}

	- (void)setInferTopSafeAreaInsetFromViewController:(BOOL)inferTopSafeAreaInsetFromViewController {
	[super setInferTopSafeAreaInsetFromViewController:inferTopSafeAreaInsetFromViewController];

	if (inferTopSafeAreaInsetFromViewController) {
	self.topLayoutGuideAdjustmentEnabled = YES;
	}

	_verticalConstraint.active = !self.inferTopSafeAreaInsetFromViewController;
	_topSafeAreaConstraint.active = self.inferTopSafeAreaInsetFromViewController;
	}

	- (void)setHeaderStackViewOffset:(CGFloat)headerStackViewOffset {
	_headerStackViewOffset = headerStackViewOffset;
	_verticalConstraint.constant = [self verticalContraintLength];
	_topSafeAreaConstraint.constant = [self topSafeAreaContraintLength];
	}

	#pragma mark - Resource bundle

	+ (NSBundle *)bundle {
	static NSBundle *bundle = nil;
	static dispatch_once_t onceToken;
	dispatch_once(&onceToken, ^{
	bundle = [NSBundle bundleWithPath:[self bundlePathWithName:kMaterialAppBarBundle]];
	});

	return bundle;
	}

	+ (NSString )bundlePathWithName:(NSString )bundleName {
	// In iOS 8+, we could be included by way of a dynamic framework, and our resource bundles may
	// not be in the main .app bundle, but rather in a nested framework, so figure out where we live
	// and use that as the search location.
	NSBundle *bundle = [NSBundle bundleForClass:[MDCAppBar class]];
	NSString *resourcePath = [(nil == bundle ? [NSBundle mainBundle] : bundle) resourcePath];
	return [resourcePath stringByAppendingPathComponent:bundleName];
	}

	#pragma mark - UIViewController Overrides

	- (void)viewDidLoad {
	[super viewDidLoad];

	[self.view addSubview:self.headerStackView];

	// Bar stack expands vertically, but has a margin above it for the status bar.
	NSArray<NSLayoutConstraint > horizontalConstraints = [NSLayoutConstraint
	constraintsWithVisualFormat:[NSString stringWithFormat:@"H:\|[%@]\|", kBarStackKey]
	options:0
	metrics:nil
	views:@{kBarStackKey : self.headerStackView}];
	[self.view addConstraints:horizontalConstraints];

	CGFloat topMargin = [self verticalContraintLength];
	_verticalConstraint = [NSLayoutConstraint constraintWithItem:self.headerStackView
	attribute:NSLayoutAttributeTop
	relatedBy:NSLayoutRelationEqual
	toItem:self.view
	attribute:NSLayoutAttributeTop
	multiplier:1
	constant:topMargin];
	_verticalConstraint.active = !self.inferTopSafeAreaInsetFromViewController;

	_topSafeAreaConstraint =
	[NSLayoutConstraint constraintWithItem:self.headerStackView
	attribute:NSLayoutAttributeTop
	relatedBy:NSLayoutRelationEqual
	toItem:self.headerView.topSafeAreaGuide
	attribute:NSLayoutAttributeBottom
	multiplier:1
	constant:[self topSafeAreaContraintLength]];
	_topSafeAreaConstraint.active = self.inferTopSafeAreaInsetFromViewController;

	[NSLayoutConstraint constraintWithItem:self.headerStackView
	attribute:NSLayoutAttributeBottom
	relatedBy:NSLayoutRelationEqual
	toItem:self.view
	attribute:NSLayoutAttributeBottom
	multiplier:1
	constant:0]
	.active = YES;
	}

	- (void)viewWillAppear:(BOOL)animated {
	[super viewWillAppear:animated];

	UIBarButtonItem *backBarButtonItem = [self backButtonItem];
	if (backBarButtonItem && !self.navigationBar.backItem) {
	self.navigationBar.backItem = backBarButtonItem;
	}
	}

	- (void)viewWillLayoutSubviews {
	[super viewWillLayoutSubviews];

	if (@available(iOS 11.0, *)) {
	// We only update the top inset on iOS 11 because previously we were not adjusting the header
	// height to make it smaller when the status bar is hidden.
	_verticalConstraint.constant = [self verticalContraintLength];
	}

	if (self.shouldAdjustHeightBasedOnHeaderStackView) {
	[self adjustHeightBasedOnHeaderStackView];
	}
	}

	- (void)didMoveToParentViewController:(UIViewController *)parent {
	[super didMoveToParentViewController:parent];

	[self.navigationBar observeNavigationItem:parent.navigationItem];

	CGRect frame = self.view.frame;
	frame.size.width = CGRectGetWidth(parent.view.bounds);
	self.view.frame = frame;
	}

	#pragma mark - UIAccessibility

	- (BOOL)accessibilityPerformEscape {
	if (self.accessibilityPerformEscapeDelegate) {
	return [self.accessibilityPerformEscapeDelegate
	appBarViewControllerAccessibilityPerformEscape:self];
	}

	// Fall-back behavior.
	[self dismissSelf];
	return YES;
	}

	#pragma mark User actions

	- (void)didTapBackButton:(__unused id)sender {
	[self dismissSelf];
	}

	- (void)dismissSelf {
	UIViewController *pvc = self.parentViewController;
	if (pvc.navigationController && pvc.navigationController.viewControllers.count > 1) {
	[pvc.navigationController popViewControllerAnimated:YES];
	} else {
	[pvc dismissViewControllerAnimated:YES completion:nil];
	}
	}

	#pragma mark - Private

	- (CGFloat)verticalContraintLength {
	return MDCDeviceTopSafeAreaInset() + _headerStackViewOffset;
	}

	- (CGFloat)topSafeAreaContraintLength {
	return _headerStackViewOffset;
	}

	- (void)adjustHeightBasedOnHeaderStackView {
	CGFloat heightSum = 0;
	heightSum += [self.headerStackView.topBar sizeThatFits:self.view.bounds.size].height;
	heightSum += [self.headerStackView.bottomBar sizeThatFits:self.view.bounds.size].height;
	heightSum += _headerStackViewOffset;
	self.headerView.minimumHeight = heightSum;
	self.headerView.maximumHeight = heightSum;
	}

	@end

	#pragma mark - To be deprecated

	@implementation MDCAppBar

	- (instancetype)init {
	self = [super init];
	if (self) {
	_appBarViewController = [[MDCAppBarViewController alloc] init];
	}
	return self;
	}

	- (MDCFlexibleHeaderViewController *)headerViewController {
	return self.appBarViewController;
	}

	- (MDCHeaderStackView *)headerStackView {
	return self.appBarViewController.headerStackView;
	}

	- (MDCNavigationBar *)navigationBar {
	return self.appBarViewController.navigationBar;
	}

	- (void)addSubviewsToParent {
	MDCAppBarViewController *abvc = self.appBarViewController;
	NSAssert(abvc.parentViewController,
	@"appBarViewController does not have a parentViewController. "
	@"Use [self addChildViewController:appBar.appBarViewController]. "
	@"This warning only appears in DEBUG builds");
	if (abvc.view.superview == abvc.parentViewController.view) {
	return;
	}

	// Enforce the header's desire to fully cover the width of its parent view.
	CGRect frame = abvc.view.frame;
	frame.origin.x = 0;
	frame.size.width = abvc.parentViewController.view.bounds.size.width;
	abvc.view.frame = frame;

	[abvc.parentViewController.view addSubview:abvc.view];
	[abvc didMoveToParentViewController:abvc.parentViewController];
	}

	- (void)setInferTopSafeAreaInsetFromViewController:(BOOL)inferTopSafeAreaInsetFromViewController {
	self.appBarViewController.inferTopSafeAreaInsetFromViewController =
	inferTopSafeAreaInsetFromViewController;
	}

	- (BOOL)inferTopSafeAreaInsetFromViewController {
	return self.appBarViewController.inferTopSafeAreaInsetFromViewController;
	}

	@end