[Ripple] Add traitCollectionDidChange block (#8062)

Adds a traitCollectionDidChangeBlock to MDCRippleView and its subclass, called when its trait collection changes.

Closes #8043

components/Ripple/src/MDCRippleView.h

@@ -73,6 +73,13 @@ typedef NS_ENUM(NSInteger, MDCRippleStyle) {
  */
 @property(nonatomic, strong, nonnull) UIColor *activeRippleColor;
 
+/**
+ A block that is invoked when the @c MDCRippleView receives a call to @c
+ traitCollectionDidChange:. The block is called after the call to the superclass.
+ */
+@property(nonatomic, copy, nullable) void (^traitCollectionDidChangeBlock)
+    (MDCRippleView *_Nonnull ripple, UITraitCollection *_Nullable previousTraitCollection);
+
 /**
  Cancels all the existing ripples.
 
@@ -121,6 +128,7 @@ typedef NS_ENUM(NSInteger, MDCRippleStyle) {
  */
 - (void)beginRippleTouchUpAnimated:(BOOL)animated
                         completion:(nullable MDCRippleCompletionBlock)completion;
+
 @end
 
 /**

components/Ripple/src/MDCRippleView.m

@@ -78,6 +78,14 @@ - (void)layoutSubviews {
   self.activeRippleLayer.fillColor = self.activeRippleColor.CGColor;
 }
 
+- (void)traitCollectionDidChange:(UITraitCollection *)previousTraitCollection {
+  [super traitCollectionDidChange:previousTraitCollection];
+
+  if (self.traitCollectionDidChangeBlock) {
+    self.traitCollectionDidChangeBlock(self, previousTraitCollection);
+  }
+}
+
 - (void)layoutSublayersOfLayer:(CALayer *)layer {
   [super layoutSublayersOfLayer:layer];
   for (CALayer *sublayer in self.layer.sublayers) {

components/Ripple/tests/unit/MDCRippleViewTests.m

@@ -249,4 +249,28 @@ - (void)testMaximumRippleRadiusImpactsUnboundedRipple {
   XCTAssertEqual(rippleView.activeRippleLayer.maximumRadius, fakeRippleRadius);
 }
 
+- (void)testTraitCollectionDidChangeBlockCalledWithExpectedParameters {
+  // Given
+  MDCRippleView *testRippleView = [[MDCRippleView alloc] init];
+  XCTestExpectation *expectation =
+      [[XCTestExpectation alloc] initWithDescription:@"traitCollection"];
+  __block UITraitCollection *passedTraitCollection = nil;
+  __block MDCRippleView *passedRippleView = nil;
+  testRippleView.traitCollectionDidChangeBlock =
+      ^(MDCRippleView *_Nonnull ripple, UITraitCollection *_Nullable previousTraitCollection) {
+        passedTraitCollection = previousTraitCollection;
+        passedRippleView = ripple;
+        [expectation fulfill];
+      };
+  UITraitCollection *fakeTraitCollection = [UITraitCollection traitCollectionWithDisplayScale:7];
+
+  // When
+  [testRippleView traitCollectionDidChange:fakeTraitCollection];
+
+  // Then
+  [self waitForExpectations:@[ expectation ] timeout:1];
+  XCTAssertEqual(passedRippleView, testRippleView);
+  XCTAssertEqual(passedTraitCollection, fakeTraitCollection);
+}
+
 @end

components/Ripple/tests/unit/MDCStatefulRippleViewTests.m

@@ -149,4 +149,28 @@ - (void)testRippleHighlighted {
   XCTAssertTrue(rippleView.rippleHighlighted);
 }
 
+- (void)testTraitCollectionDidChangeBlockCalledWithExpectedParameters {
+  // Given
+  MDCStatefulRippleView *testRippleView = [[MDCStatefulRippleView alloc] init];
+  XCTestExpectation *expectation =
+      [[XCTestExpectation alloc] initWithDescription:@"traitCollection"];
+  __block UITraitCollection *passedTraitCollection = nil;
+  __block MDCRippleView *passedRippleView = nil;
+  testRippleView.traitCollectionDidChangeBlock =
+      ^(MDCRippleView *_Nonnull ripple, UITraitCollection *_Nullable previousTraitCollection) {
+        passedTraitCollection = previousTraitCollection;
+        passedRippleView = ripple;
+        [expectation fulfill];
+      };
+  UITraitCollection *fakeTraitCollection = [UITraitCollection traitCollectionWithDisplayScale:7];
+
+  // When
+  [testRippleView traitCollectionDidChange:fakeTraitCollection];
+
+  // Then
+  [self waitForExpectations:@[ expectation ] timeout:1];
+  XCTAssertEqual(passedRippleView, testRippleView);
+  XCTAssertEqual(passedTraitCollection, fakeTraitCollection);
+}
+
 @end