[BottomAppBar] add support for dynamic color. (#7975)

closes #7883.

components/BottomAppBar/src/MDCBottomAppBarView.m

@@ -83,6 +83,9 @@ - (void)commonMDCBottomAppBarViewInit {
   [self addFloatingButton];
   [self addBottomBarLayer];
   [self addNavBar];
+
+  self.barTintColor = UIColor.whiteColor;
+  self.shadowColor = UIColor.blackColor;
 }
 
 - (void)addFloatingButton {
@@ -251,6 +254,9 @@ - (void)layoutSubviews {
   self.floatingButton.center =
       [self getFloatingButtonCenterPositionForAppBarWidth:CGRectGetWidth(self.bounds)];
   [self renderPathBasedOnFloatingButtonVisibitlityAnimated:NO];
+
+  self.bottomBarLayer.fillColor = self.barTintColor.CGColor;
+  self.bottomBarLayer.shadowColor = self.shadowColor.CGColor;
 }
 
 - (UIEdgeInsets)mdc_safeAreaInsets {
@@ -384,13 +390,10 @@ - (void)setTrailingBarButtonItems:(NSArray<UIBarButtonItem *> *)trailingBarButto
 }
 
 - (void)setBarTintColor:(UIColor *)barTintColor {
+  _barTintColor = barTintColor;
   _bottomBarLayer.fillColor = barTintColor.CGColor;
 }
 
-- (UIColor *)barTintColor {
-  return [UIColor colorWithCGColor:_bottomBarLayer.fillColor];
-}
-
 - (void)setLeadingBarItemsTintColor:(UIColor *)leadingBarItemsTintColor {
   NSParameterAssert(leadingBarItemsTintColor);
   if (!leadingBarItemsTintColor) {
@@ -416,13 +419,10 @@ - (UIColor *)trailingBarItemsTintColor {
 }
 
 - (void)setShadowColor:(UIColor *)shadowColor {
+  _shadowColor = shadowColor;
   _bottomBarLayer.shadowColor = shadowColor.CGColor;
 }
 
-- (UIColor *)shadowColor {
-  return [UIColor colorWithCGColor:_bottomBarLayer.shadowColor];
-}
-
 #pragma mark TraitCollection
 
 - (void)traitCollectionDidChange:(UITraitCollection *)previousTraitCollection {

components/BottomAppBar/tests/snapshot/MDCBottomAppBarSnapshotTests.m

@@ -163,4 +163,41 @@ - (void)testFloatingButtonElevationSecondaryRTL {
   [self generateSnapshotAndVerifyForView:self.appBar];
 }
 
+- (void)testDynamicColorSupportOniOS13AndAbove {
+#if defined(__IPHONE_13_0) && (__IPHONE_OS_VERSION_MAX_ALLOWED >= __IPHONE_13_0)
+  if (@available(iOS 13.0, *)) {
+    // Given
+    UIColor *barTintDynamicColor =
+        [UIColor colorWithDynamicProvider:^(UITraitCollection *traitCollection) {
+          if (traitCollection.userInterfaceStyle == UIUserInterfaceStyleLight) {
+            return UIColor.blackColor;
+          } else {
+            return UIColor.purpleColor;
+          }
+        }];
+    UIColor *shadowDynamicColor =
+        [UIColor colorWithDynamicProvider:^(UITraitCollection *traitCollection) {
+          if (traitCollection.userInterfaceStyle == UIUserInterfaceStyleLight) {
+            return UIColor.blackColor;
+          } else {
+            return UIColor.blueColor;
+          }
+        }];
+    self.appBar.barTintColor = barTintDynamicColor;
+    self.appBar.shadowColor = shadowDynamicColor;
+
+    // When
+    self.appBar.overrideUserInterfaceStyle = UIUserInterfaceStyleDark;
+
+    // Then
+    CGSize aSize = [self.appBar sizeThatFits:CGSizeMake(360, INFINITY)];
+    self.appBar.bounds = CGRectMake(0, 0, aSize.width, aSize.height);
+    [self.appBar layoutIfNeeded];
+    UIView *snapshotView =
+        [self.appBar mdc_addToBackgroundViewWithInsets:UIEdgeInsetsMake(50, 50, 50, 50)];
+    [self snapshotVerifyViewForIOS13:snapshotView];
+  }
+#endif
+}
+
 @end