[TabBarView] Add titleFontForState APIs (#7757)

Adds `titleFont:forState:` APIs to customize the font of selected and unselected items generally. A future change may enable support for `-[UIBarItem titleTextAttributesForState:]`.

## Dragons Example View Controller

|Before|After|
|---|---|
|![Simulator Screen Shot - iPhone 7 - 2019-06-30 at 22 38 45](https://user-images.githubusercontent.com/1753199/60407218-e9634c80-9b87-11e9-9bef-10c2449002a7.png)|![Simulator Screen Shot - iPhone 7 - 2019-06-30 at 22 39 36](https://user-images.githubusercontent.com/1753199/60407236-f718d200-9b87-11e9-8380-195235c9494e.png)|


Part of #7657

MaterialComponentsBeta.podspec

@@ -117,6 +117,7 @@ Pod::Spec.new do |mdc|
       unit_tests.source_files = [
         "components/#{extension.base_name.split('+')[0]}/tests/unit/#{extension.base_name.split('+')[1]}/*.{h,m,swift}",
       ]
+      unit_tests.dependency "MaterialComponents/Typography"
     end
   end
 

components/Tabs/BUILD

@@ -201,6 +201,7 @@ mdc_objc_library(
     deps = [
         ":TabBarView",
         ":privateTabBarView",
+        "//components/Typography",
     ],
 )
 

components/Tabs/examples/MDCTabBarViewTypicalExampleViewController.m

@@ -83,6 +83,8 @@ - (void)viewDidLoad {
                         forState:UIControlStateNormal];
   [self.tabBar setImageTintColor:self.containerScheme.colorScheme.primaryColor
                         forState:UIControlStateSelected];
+  [self.tabBar setTitleFont:self.containerScheme.typographyScheme.button
+                   forState:UIControlStateNormal];
   self.tabBar.selectedItem = item4;
   self.tabBar.translatesAutoresizingMaskIntoConstraints = NO;
   [self.view addSubview:self.tabBar];

components/Tabs/src/TabBarView/MDCTabBarView.h

@@ -68,4 +68,20 @@ __attribute__((objc_subclassing_restricted)) @interface MDCTabBarView : UIScroll
  */
 - (nullable UIColor *)titleColorForState:(UIControlState)state;
 
+/**
+ Sets the font of the bar items' title for the given control state.  Supports
+ @c UIControlStateNormal and @c UIControlStateSelected.
+
+ If no value for a control state is set, the value for @c UIControlStateNormal is used. If no value
+ for @c UIControlStateNormal is set, then a default value is used.
+ */
+- (void)setTitleFont:(nullable UIFont *)titleFont forState:(UIControlState)state;
+
+/**
+ Returns the font of the bar items' title for the given control state.
+
+ If no value for a control state is set, the value for @c UIControlStateNormal is returned.
+ */
+- (nullable UIFont *)titleFontForState:(UIControlState)state;
+
 @end

components/Tabs/src/TabBarView/MDCTabBarView.m

@@ -48,6 +48,9 @@ @interface MDCTabBarView ()
 /** The image tint colors for bar items. */
 @property(nonnull, nonatomic, strong)
     NSMutableDictionary<NSNumber *, UIColor *> *stateToImageTintColor;
+
+/** The title font for bar items. */
+@property(nonnull, nonatomic, strong) NSMutableDictionary<NSNumber *, UIFont *> *stateToTitleFont;
 @end
 
 @implementation MDCTabBarView
@@ -63,6 +66,7 @@ - (instancetype)init {
     _items = @[];
     _stateToImageTintColor = [NSMutableDictionary dictionary];
     _stateToTitleColor = [NSMutableDictionary dictionary];
+    _stateToTitleFont = [NSMutableDictionary dictionary];
     self.backgroundColor = UIColor.whiteColor;
     self.showsHorizontalScrollIndicator = NO;
 
@@ -252,6 +256,41 @@ - (UIColor *)titleColorForState:(UIControlState)state {
   return titleColor;
 }
 
+- (void)updateTitleFontForAllViews {
+  for (UITabBarItem *item in self.items) {
+    NSUInteger indexOfItem = [self.items indexOfObject:item];
+    // This is a significant error, but defensive coding is preferred.
+    if (indexOfItem == NSNotFound || indexOfItem >= self.containerView.arrangedSubviews.count) {
+      NSAssert(NO, @"Unable to find associated item view for (%@)", item);
+      continue;
+    }
+    UIView *itemView = self.containerView.arrangedSubviews[indexOfItem];
+    // Skip custom views
+    if (![itemView isKindOfClass:[MDCTabBarViewItemView class]]) {
+      continue;
+    }
+    MDCTabBarViewItemView *tabBarViewItemView = (MDCTabBarViewItemView *)itemView;
+    if (item == self.selectedItem) {
+      tabBarViewItemView.titleLabel.font = [self titleFontForState:UIControlStateSelected];
+    } else {
+      tabBarViewItemView.titleLabel.font = [self titleFontForState:UIControlStateNormal];
+    }
+  }
+}
+
+- (void)setTitleFont:(UIFont *)titleFont forState:(UIControlState)state {
+  self.stateToTitleFont[@(state)] = titleFont;
+  [self updateTitleFontForAllViews];
+}
+
+- (UIFont *)titleFontForState:(UIControlState)state {
+  UIFont *titleFont = self.stateToTitleFont[@(state)];
+  if (!titleFont) {
+    titleFont = self.stateToTitleFont[@(UIControlStateNormal)];
+  }
+  return titleFont;
+}
+
 #pragma mark - Key-Value Observing (KVO)
 
 - (void)addObserversToTabBarItems {

components/Tabs/tests/snapshot/TabBarView/MDCTabBarViewSnapshotTests.m

@@ -267,6 +267,8 @@ - (void)testChangingSelectedImageOfSelectedItemAfterAddingToBarDoesNothing {
   [self generateSnapshotAndVerifyForView:self.tabBarView];
 }
 
+#pragma mark - Layout Sizes
+
 // TODO(https://github.com/material-components/material-components-ios/issues/7717): This golden
 // is incorrect due to a suspected bug in MDCTabBarViewItemView.
 - (void)testSettingBoundsTooNarrowWithItemsLessThanMinimumWidthResultsInScrollableLayout {
@@ -489,6 +491,58 @@ - (void)testSetImageTintColorExplicitlyToNilUsesTintColor {
   [self generateSnapshotAndVerifyForView:self.tabBarView];
 }
 
+- (void)testSetTitleFontForExplicitItemStates {
+  // Given
+  UITabBarItem *item1 = [[UITabBarItem alloc] initWithTitle:@"One" image:self.typicalIcon1 tag:0];
+  UITabBarItem *item2 = [[UITabBarItem alloc] initWithTitle:@"Two" image:self.typicalIcon2 tag:2];
+  UITabBarItem *item3 = [[UITabBarItem alloc] initWithTitle:@"Three" image:self.typicalIcon3 tag:3];
+  self.tabBarView.items = @[ item1, item2, item3 ];
+  [self.tabBarView setSelectedItem:item2 animated:NO];
+
+  // When
+  [self.tabBarView setTitleFont:[UIFont systemFontOfSize:8] forState:UIControlStateNormal];
+  [self.tabBarView setTitleFont:[UIFont systemFontOfSize:24] forState:UIControlStateSelected];
+  [self.tabBarView sizeToFit];
+
+  // Then
+  [self generateSnapshotAndVerifyForView:self.tabBarView];
+}
+
+- (void)testSetTitleFontForNormalStateAppliesToSelectedItem {
+  // Given
+  UITabBarItem *item1 = [[UITabBarItem alloc] initWithTitle:@"One" image:self.typicalIcon1 tag:0];
+  UITabBarItem *item2 = [[UITabBarItem alloc] initWithTitle:@"Two" image:self.typicalIcon2 tag:2];
+  UITabBarItem *item3 = [[UITabBarItem alloc] initWithTitle:@"Three" image:self.typicalIcon3 tag:3];
+  self.tabBarView.items = @[ item1, item2, item3 ];
+  [self.tabBarView setSelectedItem:item2 animated:NO];
+
+  // When
+  [self.tabBarView setTitleFont:[UIFont systemFontOfSize:8] forState:UIControlStateNormal];
+  [self.tabBarView sizeToFit];
+
+  // Then
+  [self generateSnapshotAndVerifyForView:self.tabBarView];
+}
+
+- (void)testSetTitleFontExplicitlyToNilUsesDefaultFont {
+  // Given
+  UITabBarItem *item1 = [[UITabBarItem alloc] initWithTitle:@"One" image:self.typicalIcon1 tag:0];
+  UITabBarItem *item2 = [[UITabBarItem alloc] initWithTitle:@"Two" image:self.typicalIcon2 tag:2];
+  UITabBarItem *item3 = [[UITabBarItem alloc] initWithTitle:@"Three" image:self.typicalIcon3 tag:3];
+  self.tabBarView.items = @[ item1, item2, item3 ];
+  [self.tabBarView setSelectedItem:item2 animated:NO];
+  [self.tabBarView setTitleFont:[UIFont systemFontOfSize:8] forState:UIControlStateNormal];
+  [self.tabBarView setTitleFont:[UIFont systemFontOfSize:24] forState:UIControlStateSelected];
+
+  // When
+  [self.tabBarView setTitleFont:nil forState:UIControlStateNormal];
+  [self.tabBarView setTitleFont:nil forState:UIControlStateSelected];
+  [self.tabBarView sizeToFit];
+
+  // Then
+  [self generateSnapshotAndVerifyForView:self.tabBarView];
+}
+
 - (void)testChangingSelectionUpdatesItemStyle {
   // Given
   self.tabBarView.bounds = CGRectMake(0, 0, 360, kExpectedHeightTitlesAndIcons);

components/Tabs/tests/unit/TabBarView/MDCTabBarViewTests.m

@@ -17,6 +17,7 @@
 #import "../../../src/TabBarView/private/MDCTabBarViewItemView.h"
 #import "MDCTabBarView.h"
 #import "MDCTabBarViewDelegate.h"
+#import "MaterialTypography.h"
 
 // Minimum height of the MDCTabBar view.
 static const CGFloat kMinHeight = 48;
@@ -382,6 +383,67 @@ - (void)testTitleColorForStateWithNoValuesReturnsNil {
   XCTAssertNil([self.tabBarView titleColorForState:UIControlStateSelected]);
 }
 
+- (void)testTitleFontForStateFallsBackToNormalState {
+  // Given
+  UIFont *fakeFont = [UIFont systemFontOfSize:25];
+  [self.tabBarView setTitleFont:nil forState:UIControlStateNormal];
+  [self.tabBarView setTitleFont:nil forState:UIControlStateSelected];
+
+  // When
+  [self.tabBarView setTitleFont:fakeFont forState:UIControlStateNormal];
+
+  // Then
+  [self assertTitleFontForState:UIControlStateSelected equalsFont:fakeFont];
+}
+
+- (void)testTitleFontForStateReturnsExpectedValue {
+  // Given
+  UIFont *fakeNormalFont = [UIFont systemFontOfSize:25];
+  UIFont *fakeSelectedFont = [UIFont systemFontOfSize:24];
+  [self.tabBarView setTitleFont:nil forState:UIControlStateNormal];
+  [self.tabBarView setTitleFont:nil forState:UIControlStateSelected];
+
+  // When
+  [self.tabBarView setTitleFont:fakeNormalFont forState:UIControlStateNormal];
+  [self.tabBarView setTitleFont:fakeSelectedFont forState:UIControlStateSelected];
+
+  // Then
+  [self assertTitleFontForState:UIControlStateNormal equalsFont:fakeNormalFont];
+  [self assertTitleFontForState:UIControlStateSelected equalsFont:fakeSelectedFont];
+}
+
+- (void)testTitleFontForStateSetToNilFallsBackToNormal {
+  // Given
+  UIFont *fakeNormalFont = [UIFont systemFontOfSize:25];
+  UIFont *fakeSelectedFont = [UIFont systemFontOfSize:24];
+  [self.tabBarView setTitleFont:nil forState:UIControlStateNormal];
+  [self.tabBarView setTitleFont:fakeSelectedFont forState:UIControlStateSelected];
+
+  // When
+  [self.tabBarView setTitleFont:fakeNormalFont forState:UIControlStateNormal];
+  [self.tabBarView setTitleFont:nil forState:UIControlStateSelected];
+
+  // Then
+  [self assertTitleFontForState:UIControlStateNormal equalsFont:fakeNormalFont];
+  [self assertTitleFontForState:UIControlStateSelected equalsFont:fakeNormalFont];
+}
+
+- (void)testTitleFontForStateWithNoValuesReturnsNil {
+  // When
+  [self.tabBarView setTitleFont:nil forState:UIControlStateNormal];
+  [self.tabBarView setTitleFont:nil forState:UIControlStateSelected];
+
+  // Then
+  XCTAssertNil([self.tabBarView titleColorForState:UIControlStateNormal]);
+  XCTAssertNil([self.tabBarView titleColorForState:UIControlStateSelected]);
+}
+
+- (void)assertTitleFontForState:(UIControlState)state equalsFont:(UIFont *)font {
+  UIFont *statefulTitleFont = [self.tabBarView titleFontForState:state];
+  XCTAssertTrue([statefulTitleFont mdc_isSimplyEqual:font], @"(%@) is not equal to (%@)",
+                statefulTitleFont, font);
+}
+
 #pragma mark - Delegate
 
 - (void)testReturnNoForShouldSelectItemPreventsSelection {