[NavDrawer] Allow touch events to propagate to delegate for MDCBottom…

…NavigationDrawer (material-components#8486)

Allow the drawer to optionally forward touch events to the delegate for handling. This enables tap thru to the underlying VC if the client needs that behavior.

An example use case would be when the client wants to present the drawer on top of a VC that has controls that they want to still be tappable. For example: A video player or a podcast player with play/pause controls. Then the client VC could still receive the tap event on the control and respond to that and close the drawer at the same time. This would allow the user to save a tap.

components/NavigationDrawer/src/MDCBottomDrawerPresentationController.h

@@ -163,6 +163,24 @@
  */
 @property(nonatomic, assign) CGFloat maximumInitialDrawerHeight;
 
+/**
+ A flag allowing clients to opt-out of the drawer closing when the user taps outside the content.
+
+ @default YES The drawer should autohide on tap.
+ */
+@property(nonatomic, assign) BOOL shouldAutoDismissOnTap;
+
+/**
+ A flag allowing clients to opt-in to handling touch events.
+
+ @default NO The drawer will not forward touch events.
+
+ @discussion If set to YES and the delegate is an instance of @UIResponder, then the touch events
+ will be forwarded along to the delegate. Note: @shouldAutoDismissOnTap should also be set to NO
+ so that the events will propagate properly.
+ */
+@property(nonatomic, assign) BOOL shouldForwardTouchEvents;
+
 /**
  A flag allowing clients to opt-in to the drawer adding additional height to the content to include
  the bottom safe area inset. This will remove the need for clients to calculate their content size

components/NavigationDrawer/src/MDCBottomDrawerPresentationController.m

@@ -22,6 +22,25 @@
 static CGFloat kTopHandleWidth = (CGFloat)24.0;
 static CGFloat kTopHandleTopMargin = (CGFloat)5.0;
 
+/**
+ View that allows touches that aren't handled from within the view to be propagated up the
+ responder chain. This is used to allow forwarding of tap events from the scrim view through to
+ the delegate if that has been enabled on the VC.
+ */
+@interface MDCBottomDrawerScrimView : UIView
+@end
+
+@implementation MDCBottomDrawerScrimView
+
+- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event {
+  // Allow unhandled touches to propagate along the responder chain and optionally be handled by
+  // the drawer delegate.
+  UIView *view = [super hitTest:point withEvent:event];
+  return view == self ? nil : view;
+}
+
+@end
+
 @interface MDCBottomDrawerPresentationController () <UIGestureRecognizerDelegate,
                                                      MDCBottomDrawerContainerViewControllerDelegate>
 
@@ -55,6 +74,7 @@ - (instancetype)initWithPresentedViewController:(UIViewController *)presentedVie
     _maximumInitialDrawerHeight = 0;
     _drawerShadowColor = [UIColor.blackColor colorWithAlphaComponent:(CGFloat)0.2];
     _elevation = MDCShadowElevationNavDrawer;
+    _shouldAutoDismissOnTap = YES;
   }
   return self;
 }
@@ -102,7 +122,7 @@ - (void)presentationTransitionWillBegin {
   self.bottomDrawerContainerViewController = bottomDrawerContainerViewController;
   self.bottomDrawerContainerViewController.delegate = self;
 
-  self.scrimView = [[UIView alloc] initWithFrame:self.containerView.bounds];
+  self.scrimView = [[MDCBottomDrawerScrimView alloc] initWithFrame:self.containerView.bounds];
   self.scrimView.backgroundColor =
       self.scrimColor ?: [UIColor colorWithWhite:0 alpha:(CGFloat)0.32];
   self.scrimView.autoresizingMask =
@@ -184,19 +204,20 @@ - (void)presentationTransitionWillBegin {
 }
 
 - (void)presentationTransitionDidEnd:(BOOL)completed {
-  // Set up the tap recognizer to dimiss the drawer by.
-  UITapGestureRecognizer *tapGestureRecognizer =
-      [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(hideDrawer)];
-  [self.containerView addGestureRecognizer:tapGestureRecognizer];
-  tapGestureRecognizer.delegate = self;
+  if (self.shouldAutoDismissOnTap) {
+    // Set up the tap recognizer to dimiss the drawer by.
+    UITapGestureRecognizer *tapGestureRecognizer =
+        [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(hideDrawer)];
+    [self.containerView addGestureRecognizer:tapGestureRecognizer];
+    tapGestureRecognizer.delegate = self;
+  }
 
   self.bottomDrawerContainerViewController.animatingPresentation = NO;
   [self.bottomDrawerContainerViewController.view setNeedsLayout];
   if (!completed) {
     [self.scrimView removeFromSuperview];
     [self.topHandle removeFromSuperview];
   }
-
   [self.delegate bottomDrawerPresentTransitionDidEnd:self];
 }
 

components/NavigationDrawer/src/MDCBottomDrawerViewController.h

@@ -86,6 +86,23 @@
  */
 @property(nonatomic, assign) CGFloat maximumInitialDrawerHeight;
 
+/**
+ A flag allowing clients to opt-out of the drawer closing when the user taps outside the content.
+
+ @default YES The drawer should autohide on tap.
+ */
+@property(nonatomic, assign) BOOL shouldAutoDismissOnTap;
+
+/**
+ A flag allowing clients to opt-in to handling touch events.
+
+ @default NO The drawer will not forward touch events.
+
+ @discussion If set to YES and the delegate is an instance of @UIResponder, then the touch events
+ will be forwarded along to the delegate.
+ */
+@property(nonatomic, assign) BOOL shouldForwardTouchEvents;
+
 /**
  A flag allowing clients to opt-in to the drawer adding additional height to the content to include
  the bottom safe area inset. This will remove the need for clients to calculate their content size

components/NavigationDrawer/src/MDCBottomDrawerViewController.m

@@ -34,6 +34,9 @@ @implementation MDCBottomDrawerViewController {
   // Used for tracking the presentation/dismissal animations.
   BOOL _isDrawerClosed;
   CGFloat _lastOffset;
+
+  // Used for forwarding touch events if enabled.
+  __weak UIResponder *_cachedNextResponder;
 }
 
 @synthesize mdc_overrideBaseElevation = _mdc_overrideBaseElevation;
@@ -67,6 +70,8 @@ - (void)commonMDCBottomDrawerViewControllerInit {
   _mdc_overrideBaseElevation = -1;
   _isDrawerClosed = YES;
   _lastOffset = NSNotFound;
+  _shouldAutoDismissOnTap = YES;
+  _shouldForwardTouchEvents = NO;
 }
 
 - (void)viewWillLayoutSubviews {
@@ -201,6 +206,15 @@ - (void)setMaximumInitialDrawerHeight:(CGFloat)maximumInitialDrawerHeight {
   }
 }
 
+- (void)setShouldAutoDismissOnTap:(BOOL)shouldAutoDismissOnTap {
+  _shouldAutoDismissOnTap = shouldAutoDismissOnTap;
+  if ([self.presentationController isKindOfClass:[MDCBottomDrawerPresentationController class]]) {
+    MDCBottomDrawerPresentationController *bottomDrawerPresentationController =
+        (MDCBottomDrawerPresentationController *)self.presentationController;
+    bottomDrawerPresentationController.shouldAutoDismissOnTap = self.shouldAutoDismissOnTap;
+  }
+}
+
 - (void)setElevation:(MDCShadowElevation)elevation {
   _elevation = elevation;
   if ([self.presentationController isKindOfClass:[MDCBottomDrawerPresentationController class]]) {
@@ -224,6 +238,21 @@ - (void)setShouldAlwaysExpandHeader:(BOOL)shouldAlwaysExpandHeader {
   }
 }
 
+- (void)setDelegate:(id<MDCBottomDrawerViewControllerDelegate>)delegate {
+  _delegate = delegate;
+  if ([delegate isKindOfClass:[UIResponder class]]) {
+    _cachedNextResponder = (UIResponder *)delegate;
+  }
+}
+
+- (UIResponder *)nextResponder {
+  // Allow the delegate to opt-in to the responder chain to handle events.
+  if (self.shouldForwardTouchEvents && _cachedNextResponder) {
+    return _cachedNextResponder;
+  }
+  return [super nextResponder];
+}
+
 - (CGFloat)mdc_currentElevation {
   return self.elevation;
 }

components/NavigationDrawer/src/private/MDCBottomDrawerContainerViewController.m

@@ -52,6 +52,26 @@ - (MDCShadowLayer *)shadowLayer {
 }
 @end
 
+/**
+ View that allows touches that aren't handled from within the view to be propagated up the
+ responder chain. This is used to allow forwarding of tap events from the scroll view through to
+ the delegate if that has been enabled on the VC.
+ */
+
+@interface MDCBottomDrawerScrollView : UIScrollView
+@end
+
+@implementation MDCBottomDrawerScrollView
+
+- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event {
+  // Allow unhandled touches to propagate along the responder chain and optionally be handled by
+  // the drawer delegate.
+  UIView *view = [super hitTest:point withEvent:event];
+  return view == self ? nil : view;
+}
+
+@end
+
 @interface MDCBottomDrawerContainerViewController (LayoutCalculations)
 
 /**
@@ -758,7 +778,7 @@ - (void)updateContentWithHeight:(CGFloat)height {
 
 - (UIScrollView *)scrollView {
   if (!_scrollView) {
-    _scrollView = [[UIScrollView alloc] init];
+    _scrollView = [[MDCBottomDrawerScrollView alloc] init];
     _scrollView.showsVerticalScrollIndicator = NO;
     _scrollView.alwaysBounceVertical = YES;
     _scrollView.backgroundColor = [UIColor clearColor];

components/NavigationDrawer/tests/unit/MDCNavigationDrawerScrollViewTests.m

@@ -685,6 +685,20 @@ - (void)testSetTrackingScrollViewAfterSetScrimColor {
       drawerPresentationController.bottomDrawerContainerViewController.trackingScrollView);
 }
 
+- (void)testSetShouldAutoDismissOnTapCorrectly {
+  MDCBottomDrawerPresentationController *drawerPresentationController =
+      (MDCBottomDrawerPresentationController *)self.drawerViewController.presentationController;
+  self.drawerViewController.shouldAutoDismissOnTap = YES;
+  XCTAssertTrue(drawerPresentationController.shouldAutoDismissOnTap);
+}
+
+- (void)testSetShouldForwardTouchEventsCorrectly {
+  XCTAssertNil(self.drawerViewController.nextResponder);
+  self.drawerViewController.shouldForwardTouchEvents = YES;
+  XCTAssertEqualObjects(self.drawerViewController.delegate,
+                        self.drawerViewController.nextResponder);
+}
+
 - (void)testBottomDrawerTopInset {
   // Given
   MDCNavigationDrawerFakeHeaderViewController *fakeHeader =