[Tabs] Allow setting ripple color. (#7784)

Adds a property that customizes the ripple color.

## Example View Controller

|Before|After|
|---|---|
|![Simulator Screen Shot - iPhone X - 2019-07-03 at 00 14 24](https://user-images.githubusercontent.com/1753199/60562949-a809a300-9d27-11e9-963d-830356ed845c.png)|![Simulator Screen Shot - iPhone X - 2019-07-03 at 00 12 49](https://user-images.githubusercontent.com/1753199/60562952-ad66ed80-9d27-11e9-8013-db5dba602bf3.png)|

Closes #7657

components/Tabs/examples/MDCTabBarViewTypicalExampleViewController.m

@@ -130,6 +130,8 @@ - (void)viewDidLoad {
                    forState:UIControlStateNormal];
   [self.tabBar setTitleFont:[UIFont systemFontOfSize:16] forState:UIControlStateSelected];
   self.tabBar.selectionIndicatorStrokeColor = self.containerScheme.colorScheme.onSecondaryColor;
+  self.tabBar.rippleColor =
+      [self.containerScheme.colorScheme.primaryColor colorWithAlphaComponent:(CGFloat)0.1];
   self.tabBar.selectedItem = item4;
   self.tabBar.translatesAutoresizingMaskIntoConstraints = NO;
   [self.view addSubview:self.tabBar];

components/Tabs/src/TabBarView/MDCTabBarView.h

@@ -34,6 +34,11 @@ __attribute__((objc_subclassing_restricted)) @interface MDCTabBarView : UIScroll
 /** The color of the Tab bar's background. */
 @property(nullable, nonatomic, copy) UIColor *barTintColor;
 
+/**
+ The color for the Ripple effect for touch feedback.
+ */
+@property(nonnull, nonatomic, copy) UIColor *rippleColor;
+
 /** The tab bar view delegate. */
 @property(nullable, nonatomic, weak) id<MDCTabBarViewDelegate> tabBarDelegate;
 

components/Tabs/src/TabBarView/MDCTabBarView.m

@@ -70,6 +70,7 @@ @interface MDCTabBarView ()
 
 /** The title font for bar items. */
 @property(nonnull, nonatomic, strong) NSMutableDictionary<NSNumber *, UIFont *> *stateToTitleFont;
+
 @end
 
 @implementation MDCTabBarView
@@ -82,6 +83,7 @@ @implementation MDCTabBarView
 - (instancetype)init {
   self = [super init];
   if (self) {
+    _rippleColor = [[UIColor alloc] initWithWhite:0 alpha:(CGFloat)0.16];
     _needsScrollToSelectedItem = YES;
     _items = @[];
     _stateToImageTintColor = [NSMutableDictionary dictionary];
@@ -122,6 +124,21 @@ - (UIColor *)barTintColor {
   return self.backgroundColor;
 }
 
+- (void)updateRippleColorForAllViews {
+  for (UIView *subview in self.itemViews) {
+    if (![subview isKindOfClass:[MDCTabBarViewItemView class]]) {
+      continue;
+    }
+    MDCTabBarViewItemView *itemView = (MDCTabBarViewItemView *)subview;
+    itemView.rippleTouchController.rippleView.rippleColor = self.rippleColor;
+  }
+}
+
+- (void)setRippleColor:(UIColor *)rippleColor {
+  _rippleColor = [rippleColor copy];
+  [self updateRippleColorForAllViews];
+}
+
 - (void)setSelectionIndicatorStrokeColor:(UIColor *)selectionIndicatorStrokeColor {
   _selectionIndicatorStrokeColor = selectionIndicatorStrokeColor ?: UIColor.blackColor;
   self.selectionIndicatorView.tintColor = self.selectionIndicatorStrokeColor;
@@ -162,6 +179,7 @@ - (void)setItems:(NSArray<UITabBarItem *> *)items {
                                             : item.accessibilityTraits;
       mdcItemView.titleLabel.textColor = [self titleColorForState:UIControlStateNormal];
       mdcItemView.iconImageView.image = item.image;
+      mdcItemView.rippleTouchController.rippleView.rippleColor = self.rippleColor;
       itemView = mdcItemView;
     }
     UITapGestureRecognizer *tapGesture =

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

@@ -17,6 +17,7 @@
 #import "MDCTabBarItem.h"
 #import "MDCTabBarView.h"
 #import "MDCTabBarViewIndicatorSupporting.h"
+#import "MDCTabBarViewItemView.h"
 
 /** The typical size of an image in a Tab bar. */
 static const CGSize kTypicalImageSize = (CGSize){24, 24};
@@ -88,6 +89,11 @@ - (CGSize)sizeThatFits:(CGSize)size {
     @"وتم عل والقرى إتفاقية, عن هذا وباءت الغالي وفرنسا.";
 static NSString *const kItemTitleLong3Arabic = @"تحت أي قدما وإقامة. ودول بشرية اليابانية لان ما.";
 
+/** Exposing some internal properties to aid in testing. */
+@interface MDCTabBarView (SnapshotTesting)
+@property(nonnull, nonatomic, copy) NSArray<UIView *> *itemViews;
+@end
+
 /** A test class that allows setting safe area insets. */
 @interface MDCTabBarViewSnapshotTestsSuperview : UIView
 /** Allows overriding the safe area insets. */
@@ -182,6 +188,24 @@ - (void)tearDown {
 
 #pragma mark - Helpers
 
+- (void)activateRippleInView:(MDCTabBarView *)tabBarView forItem:(UITabBarItem *)item {
+  NSUInteger indexOfItem = [tabBarView.items indexOfObject:item];
+  if (indexOfItem == NSNotFound || indexOfItem >= tabBarView.itemViews.count) {
+    NSAssert(NO, @"(%@) has no associated item view.", item);
+    return;
+  }
+  UIView *itemView = tabBarView.itemViews[indexOfItem];
+  if (![itemView isKindOfClass:[MDCTabBarViewItemView class]]) {
+    return;
+  }
+  MDCTabBarViewItemView *mdcItemView = (MDCTabBarViewItemView *)itemView;
+  [mdcItemView.rippleTouchController.rippleView
+      beginRippleTouchDownAtPoint:CGPointMake(CGRectGetMidX(mdcItemView.bounds),
+                                              CGRectGetMidY(mdcItemView.bounds))
+                         animated:NO
+                       completion:nil];
+}
+
 - (void)changeToLatinStringsWithLongTitles:(BOOL)useLongTitles {
   if (useLongTitles) {
     self.item1.title = kItemTitleLong1Latin;
@@ -952,6 +976,23 @@ - (void)testBarTintColor {
   [self generateSnapshotAndVerifyForView:self.tabBarView];
 }
 
+- (void)testRippleColor {
+  // 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 sizeToFit];
+
+  // When
+  self.tabBarView.rippleColor = [UIColor.orangeColor colorWithAlphaComponent:(CGFloat)0.25];
+  [self activateRippleInView:self.tabBarView forItem:item1];
+
+  // Then
+  [self generateSnapshotAndVerifyForView:self.tabBarView];
+}
+
 - (void)testCustomSelectionIndicatorStrokeColor {
   // Given
   UITabBarItem *item1 = [[UITabBarItem alloc] initWithTitle:@"One" image:self.typicalIcon1 tag:0];

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

@@ -273,6 +273,12 @@ - (void)testSettingBackgroundColorUpdatesBarTintColor {
   XCTAssertEqual(self.tabBarView.barTintColor, self.tabBarView.backgroundColor);
 }
 
+- (void)testDefaultRippleColor {
+  // Then
+  XCTAssertEqualObjects(self.tabBarView.rippleColor, [[UIColor alloc] initWithWhite:0
+                                                                              alpha:(CGFloat)0.16]);
+}
+
 - (void)testImageTintColorForStateFallsBackToNormalState {
   // Given
   [self.tabBarView setImageTintColor:nil forState:UIControlStateNormal];