[Tabs] Expand configuration in MDCTabBarView example. (#8498)

Adds configuration options for `preferredLayoutStyle` and toggling
`contentInset`.

|Fewer Tabs (Portrait)|More Tabs (Landscape)|
|---|---|
|![Simulator Screen Shot - iPhone 7 - 2019-09-25 at 09 12 25](https://user-images.githubusercontent.com/1753199/65605352-f3260180-df76-11e9-8fcd-2cd68ec30fa3.png)|![Simulator Screen Shot - iPhone 7 - 2019-09-25 at 09 15 47](https://user-images.githubusercontent.com/1753199/65605434-181a7480-df77-11e9-993d-1a9c4e7a68e0.png)|


Helps exercise #8236

components/Tabs/BUILD

@@ -100,13 +100,21 @@ mdc_extension_objc_library(
     ],
 )
 
+filegroup(
+    name = "TabsExamplesAssets",
+    srcs = glob(["examples/resources/TabBarDemoAssets.xcassets/**"]),
+)
+
 mdc_examples_objc_library(
     name = "ObjcExamples",
+    data = [":TabsExamplesAssets"],
     deps = [
         ":ColorThemer",
         ":TabBarView",
         ":Tabs",
         ":TypographyThemer",
+        "//components/ActionSheet",
+        "//components/ActionSheet:Theming",
         "//components/AppBar",
         "//components/AppBar:ColorThemer",
         "//components/AppBar:TypographyThemer",
@@ -115,6 +123,7 @@ mdc_examples_objc_library(
         "//components/Collections",
         "//components/Palettes",
         "//components/Slider",
+        "//components/private/Icons/icons/ic_settings",
         "//components/private/Math",
         "//components/schemes/Color",
         "//components/schemes/Container",

components/Tabs/examples/MDCTabBarViewTypicalExampleViewController.m

@@ -14,13 +14,23 @@
 
 #import <UIKit/UIKit.h>
 
+#import <MaterialComponents/MaterialActionSheet+Theming.h>
+#import <MaterialComponents/MaterialActionSheet.h>
 #import <MaterialComponents/MaterialAnimationTiming.h>
 #import <MaterialComponents/MaterialContainerScheme.h>
+#import <MaterialComponents/MaterialIcons+ic_check.h>
+#import <MaterialComponents/MaterialIcons+ic_settings.h>
 #import <MaterialComponents/MaterialMath.h>
 #import "MaterialTabs+TabBarView.h"
 
 static NSString *const kExampleTitle = @"TabBarView";
 
+/** Accessibility label for the content insets toggle button. */
+static NSString *const kToggleContentInsetsAccessibilityLabel = @"Toggle content insets";
+
+/** Accessibility label for the preferred layout menu button. */
+static NSString *const kPreferredLayoutMenuAccessibilityLabel = @"Change preferred alignment";
+
 /** A custom view to place in an MDCTabBarView. */
 @interface MDCTabBarViewTypicalExampleViewControllerCustomView
     : UIView <MDCTabBarViewCustomViewable>
@@ -112,13 +122,28 @@ @interface MDCTabBarViewTypicalExampleViewController
 /** Tracks the UITabBarItem views that are currently on-screen. */
 @property(nonatomic, copy) NSSet<UITabBarItem *> *visibleItems;
 
+/** Image for toggle button when contentInset is non-zero. */
+@property(nonatomic, strong) UIImage *contentInsetToggleEnabledImage;
+
+/** Image for toggle button when contentInset is zero. */
+@property(nonatomic, strong) UIImage *contentInsetToggleDisabledImage;
+
 @end
 
 @implementation MDCTabBarViewTypicalExampleViewController
 
 - (void)viewDidLoad {
   [super viewDidLoad];
   self.title = kExampleTitle;
+  NSBundle *selfBundle = [NSBundle bundleForClass:[self class]];
+  self.contentInsetToggleEnabledImage = [[UIImage imageNamed:@"contentInset_enabled"
+                                                    inBundle:selfBundle
+                               compatibleWithTraitCollection:nil]
+      imageWithRenderingMode:UIImageRenderingModeAlwaysTemplate];
+  self.contentInsetToggleDisabledImage = [[UIImage imageNamed:@"contentInset_disabled"
+                                                     inBundle:selfBundle
+                                compatibleWithTraitCollection:nil]
+      imageWithRenderingMode:UIImageRenderingModeAlwaysTemplate];
 
   [self applyFixForInjectedAppBar];
 
@@ -185,6 +210,23 @@ - (void)viewDidLoad {
 
   [self applyThemingToTabBarView];
   [self addSegmentedControl];
+
+  UIBarButtonItem *alignmentButton = [[UIBarButtonItem alloc]
+      initWithImage:[MDCIcons.imageFor_ic_settings
+                        imageWithRenderingMode:UIImageRenderingModeAlwaysTemplate]
+              style:UIBarButtonItemStylePlain
+             target:self
+             action:@selector(didTapAlignmentButton)];
+  alignmentButton.accessibilityLabel = kPreferredLayoutMenuAccessibilityLabel;
+
+  UIBarButtonItem *insetsButton =
+      [[UIBarButtonItem alloc] initWithImage:self.contentInsetToggleDisabledImage
+                                       style:UIBarButtonItemStylePlain
+                                      target:self
+                                      action:@selector(didToggleInsets:)];
+  insetsButton.accessibilityLabel = kToggleContentInsetsAccessibilityLabel;
+
+  self.navigationItem.rightBarButtonItems = @[ alignmentButton, insetsButton ];
 }
 
 - (void)applyThemingToTabBarView {
@@ -272,6 +314,65 @@ - (void)applyFixForInjectedAppBar {
 
 #pragma mark - Item style variations
 
+- (void)didTapAlignmentButton {
+  MDCTabBarViewLayoutStyle currentStyle = self.tabBar.preferredLayoutStyle;
+  UIImage *checkIcon =
+      [MDCIcons.imageFor_ic_check imageWithRenderingMode:UIImageRenderingModeAlwaysTemplate];
+  MDCActionSheetController *actionSheet =
+      [MDCActionSheetController actionSheetControllerWithTitle:@"Preferred Layout Style"];
+  MDCActionSheetAction *fixedJustifiedAction = [MDCActionSheetAction
+      actionWithTitle:@"Fixed"
+                image:((currentStyle == MDCTabBarViewLayoutStyleFixed) ? checkIcon : nil)
+              handler:^(MDCActionSheetAction *_Nonnull action) {
+                self.tabBar.preferredLayoutStyle = MDCTabBarViewLayoutStyleFixed;
+              }];
+  MDCActionSheetAction *fixedClusteredLeadingAction = [MDCActionSheetAction
+      actionWithTitle:@"Fixed Clustered Leading"
+                image:((currentStyle == MDCTabBarViewLayoutStyleFixedClusteredLeading) ? checkIcon
+                                                                                       : nil)
+              handler:^(MDCActionSheetAction *_Nonnull action) {
+                self.tabBar.preferredLayoutStyle = MDCTabBarViewLayoutStyleFixedClusteredLeading;
+              }];
+  MDCActionSheetAction *fixedClusteredTrailingAction = [MDCActionSheetAction
+      actionWithTitle:@"Fixed Clustered Trailing"
+                image:((currentStyle == MDCTabBarViewLayoutStyleFixedClusteredTrailing) ? checkIcon
+                                                                                        : nil)
+              handler:^(MDCActionSheetAction *_Nonnull action) {
+                self.tabBar.preferredLayoutStyle = MDCTabBarViewLayoutStyleFixedClusteredTrailing;
+              }];
+  MDCActionSheetAction *fixedClusteredCenteredAction = [MDCActionSheetAction
+      actionWithTitle:@"Fixed Clustered Centered"
+                image:((currentStyle == MDCTabBarViewLayoutStyleFixedClusteredCentered) ? checkIcon
+                                                                                        : nil)
+              handler:^(MDCActionSheetAction *_Nonnull action) {
+                self.tabBar.preferredLayoutStyle = MDCTabBarViewLayoutStyleFixedClusteredCentered;
+              }];
+  MDCActionSheetAction *scrollableAction = [MDCActionSheetAction
+      actionWithTitle:@"Scrollable"
+                image:((currentStyle == MDCTabBarViewLayoutStyleScrollable) ? checkIcon : nil)
+              handler:^(MDCActionSheetAction *_Nonnull action) {
+                self.tabBar.preferredLayoutStyle = MDCTabBarViewLayoutStyleScrollable;
+              }];
+  [actionSheet addAction:fixedJustifiedAction];
+  [actionSheet addAction:fixedClusteredLeadingAction];
+  [actionSheet addAction:fixedClusteredTrailingAction];
+  [actionSheet addAction:fixedClusteredCenteredAction];
+  [actionSheet addAction:scrollableAction];
+  [actionSheet applyThemeWithScheme:self.containerScheme];
+  actionSheet.alwaysAlignTitleLeadingEdges = YES;
+  [self presentViewController:actionSheet animated:YES completion:nil];
+}
+
+- (void)didToggleInsets:(UIBarButtonItem *)sender {
+  if (UIEdgeInsetsEqualToEdgeInsets(self.tabBar.contentInset, UIEdgeInsetsZero)) {
+    self.tabBar.contentInset = UIEdgeInsetsMake(0, 10, 0, 30);
+    sender.image = self.contentInsetToggleEnabledImage;
+  } else {
+    self.tabBar.contentInset = UIEdgeInsetsZero;
+    sender.image = self.contentInsetToggleDisabledImage;
+  }
+}
+
 - (void)segmentedControlChangedValue:(id)sender {
   if ([sender isKindOfClass:[UISegmentedControl class]]) {
     UISegmentedControl *segmentedControl = (UISegmentedControl *)sender;

components/Tabs/examples/resources/TabBarDemoAssets.xcassets/contentInset_disabled.imageset/Contents.json

@@ -0,0 +1,23 @@
+{
+  "images" : [
+    {
+      "idiom" : "universal",
+      "filename" : "outline_crop_din_black_24pt_1x.png",
+      "scale" : "1x"
+    },
+    {
+      "idiom" : "universal",
+      "filename" : "outline_crop_din_black_24pt_2x.png",
+      "scale" : "2x"
+    },
+    {
+      "idiom" : "universal",
+      "filename" : "outline_crop_din_black_24pt_3x.png",
+      "scale" : "3x"
+    }
+  ],
+  "info" : {
+    "version" : 1,
+    "author" : "xcode"
+  }
+}

components/Tabs/examples/resources/TabBarDemoAssets.xcassets/contentInset_enabled.imageset/Contents.json

@@ -0,0 +1,23 @@
+{
+  "images" : [
+    {
+      "idiom" : "universal",
+      "filename" : "outline_view_array_black_24pt_1x.png",
+      "scale" : "1x"
+    },
+    {
+      "idiom" : "universal",
+      "filename" : "outline_view_array_black_24pt_2x.png",
+      "scale" : "2x"
+    },
+    {
+      "idiom" : "universal",
+      "filename" : "outline_view_array_black_24pt_3x.png",
+      "scale" : "3x"
+    }
+  ],
+  "info" : {
+    "version" : 1,
+    "author" : "xcode"
+  }
+}