[Tabs] Add titleColorForState: API. (#7712)

Adds a new API to affect the items' title color for `.selected` and `.normal` states.

Part of #7657

components/Tabs/src/TabBarView/MDCTabBarView.h

@@ -28,4 +28,20 @@ __attribute__((objc_subclassing_restricted)) @interface MDCTabBarView : UIScroll
 /** The color of the Tab bar's background. */
 @property(nullable, nonatomic, copy) UIColor *barTintColor;
 
+/**
+ Sets the color 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)setTitleColor:(nullable UIColor *)titleColor forState:(UIControlState)state;
+
+/**
+ Returns the color 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 UIColor *)titleColorForState:(UIControlState)state;
+
 @end

components/Tabs/src/TabBarView/MDCTabBarView.m

@@ -21,7 +21,10 @@
 @interface MDCTabBarView ()
 
 /** The views representing the items of this tab bar. */
-@property(nonatomic, strong) NSArray<UIView *> *itemViews;
+@property(nonnull, nonatomic, strong) NSArray<UIView *> *itemViews;
+
+/** The title colors for bar items. */
+@property(nonnull, nonatomic, strong) NSMutableDictionary<NSNumber *, UIColor *> *stateToTitleColor;
 
 @end
 
@@ -34,6 +37,7 @@ - (instancetype)init {
   if (self) {
     _items = @[];
     _itemViews = @[];
+    _stateToTitleColor = [NSMutableDictionary dictionary];
   }
   return self;
 }
@@ -67,6 +71,7 @@ - (void)setItems:(NSArray<UITabBarItem *> *)items {
     // TODO(#7645): Remove this if autoresizing masks are used.
     itemView.translatesAutoresizingMaskIntoConstraints = NO;
     itemView.titleLabel.text = item.title;
+    itemView.titleLabel.textColor = [self titleColorForState:UIControlStateNormal];
     itemView.iconImageView.image = item.image;
     [itemViews addObject:itemView];
     [self addSubview:itemView];
@@ -97,6 +102,42 @@ - (void)setSelectedItem:(UITabBarItem *)selectedItem {
   }
 
   _selectedItem = selectedItem;
+  [self updateTitleColorForAllViews];
+}
+
+- (void)updateTitleColorForAllViews {
+  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.itemViews.count) {
+      NSAssert(NO, @"Unable to find associated item view for (%@)", item);
+      continue;
+    }
+    UIView *itemView = self.itemViews[indexOfItem];
+    // Skip custom views
+    if (![itemView isKindOfClass:[MDCTabBarViewItemView class]]) {
+      continue;
+    }
+    MDCTabBarViewItemView *tabBarViewItemView = (MDCTabBarViewItemView *)itemView;
+    if (item == self.selectedItem) {
+      tabBarViewItemView.titleLabel.textColor = [self titleColorForState:UIControlStateSelected];
+    } else {
+      tabBarViewItemView.titleLabel.textColor = [self titleColorForState:UIControlStateNormal];
+    }
+  }
+}
+
+- (void)setTitleColor:(UIColor *)titleColor forState:(UIControlState)state {
+  self.stateToTitleColor[@(state)] = titleColor;
+  [self updateTitleColorForAllViews];
+}
+
+- (UIColor *)titleColorForState:(UIControlState)state {
+  UIColor *titleColor = self.stateToTitleColor[@(state)];
+  if (!titleColor) {
+    titleColor = self.stateToTitleColor[@(UIControlStateNormal)];
+  }
+  return titleColor;
 }
 
 #pragma mark - UIView

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

@@ -139,6 +139,74 @@ - (void)testItemsWithMixedTitlesAndImages {
 
 #pragma mark - MDCTabBarView Properties
 
+- (void)testSetTitleColorForExplicitItemStates {
+  // Given
+  self.tabBarView.bounds = CGRectMake(0, 0, 360, kExpectedHeightTitlesAndIcons);
+  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.selectedItem = item2;
+
+  // When
+  [self.tabBarView setTitleColor:UIColor.brownColor forState:UIControlStateSelected];
+  [self.tabBarView setTitleColor:UIColor.purpleColor forState:UIControlStateNormal];
+
+  // Then
+  [self generateSnapshotAndVerifyForView:self.tabBarView];
+}
+
+- (void)testSetTitleColorForNormalStateAppliesToSelectedItem {
+  // Given
+  self.tabBarView.bounds = CGRectMake(0, 0, 360, kExpectedHeightTitlesAndIcons);
+  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.selectedItem = item2;
+
+  // When
+  [self.tabBarView setTitleColor:UIColor.purpleColor forState:UIControlStateNormal];
+
+  // Then
+  [self generateSnapshotAndVerifyForView:self.tabBarView];
+}
+
+- (void)testSetTitleColorExplicitlyToNilRendersSomeDefault {
+  // Given
+  self.tabBarView.bounds = CGRectMake(0, 0, 360, kExpectedHeightTitlesAndIcons);
+  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.selectedItem = item2;
+
+  // When
+  [self.tabBarView setTitleColor:nil forState:UIControlStateNormal];
+  [self.tabBarView setTitleColor:nil forState:UIControlStateSelected];
+
+  // Then
+  [self generateSnapshotAndVerifyForView:self.tabBarView];
+}
+
+- (void)testChangingSelectionUpdatesItemStyle {
+  // Given
+  self.tabBarView.bounds = CGRectMake(0, 0, 360, kExpectedHeightTitlesAndIcons);
+  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.selectedItem = item2;
+  [self.tabBarView setTitleColor:UIColor.purpleColor forState:UIControlStateNormal];
+  [self.tabBarView setTitleColor:UIColor.brownColor forState:UIControlStateSelected];
+
+  // When
+  self.tabBarView.selectedItem = item3;
+
+  // Then
+  [self generateSnapshotAndVerifyForView:self.tabBarView];
+}
+
 - (void)testBarTintColor {
   // When
   self.tabBarView.barTintColor = UIColor.purpleColor;

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

@@ -163,4 +163,59 @@ - (void)testSettingBackgroundColorUpdatesBarTintColor {
   XCTAssertEqual(self.tabBarView.barTintColor, self.tabBarView.backgroundColor);
 }
 
+- (void)testTitleColorForStateFallsBackToNormalState {
+  // Given
+  [self.tabBarView setTitleColor:nil forState:UIControlStateNormal];
+  [self.tabBarView setTitleColor:nil forState:UIControlStateSelected];
+
+  // When
+  [self.tabBarView setTitleColor:UIColor.purpleColor forState:UIControlStateNormal];
+
+  // Then
+  XCTAssertEqualObjects([self.tabBarView titleColorForState:UIControlStateSelected],
+                        UIColor.purpleColor);
+}
+
+- (void)testTitleColorForStateReturnsExpectedValue {
+  // Given
+  [self.tabBarView setTitleColor:nil forState:UIControlStateNormal];
+  [self.tabBarView setTitleColor:nil forState:UIControlStateSelected];
+
+  // When
+  [self.tabBarView setTitleColor:UIColor.purpleColor forState:UIControlStateNormal];
+  [self.tabBarView setTitleColor:UIColor.orangeColor forState:UIControlStateSelected];
+
+  // Then
+  XCTAssertEqualObjects([self.tabBarView titleColorForState:UIControlStateNormal],
+                        UIColor.purpleColor);
+  XCTAssertEqualObjects([self.tabBarView titleColorForState:UIControlStateSelected],
+                        UIColor.orangeColor);
+}
+
+- (void)testTitleColorForStateSetToNilFallsBackToNormal {
+  // Given
+  [self.tabBarView setTitleColor:nil forState:UIControlStateNormal];
+  [self.tabBarView setTitleColor:UIColor.cyanColor forState:UIControlStateSelected];
+
+  // When
+  [self.tabBarView setTitleColor:UIColor.purpleColor forState:UIControlStateNormal];
+  [self.tabBarView setTitleColor:nil forState:UIControlStateSelected];
+
+  // Then
+  XCTAssertEqualObjects([self.tabBarView titleColorForState:UIControlStateNormal],
+                        UIColor.purpleColor);
+  XCTAssertEqualObjects([self.tabBarView titleColorForState:UIControlStateSelected],
+                        UIColor.purpleColor);
+}
+
+- (void)testTitleColorForStateWithNoValuesReturnsNil {
+  // When
+  [self.tabBarView setTitleColor:nil forState:UIControlStateNormal];
+  [self.tabBarView setTitleColor:nil forState:UIControlStateSelected];
+
+  // Then
+  XCTAssertNil([self.tabBarView titleColorForState:UIControlStateNormal]);
+  XCTAssertNil([self.tabBarView titleColorForState:UIControlStateSelected]);
+}
+
 @end