RouteObserver supports multiple RouteAware per Route. (#13757)

Unsubscribe should remove RouteAware for all routes.

packages/flutter/lib/src/widgets/routes.dart

@@ -1116,7 +1116,7 @@ abstract class PopupRoute<T> extends ModalRoute<T> {
 /// }
 /// ```
 class RouteObserver<T extends Route<dynamic>> extends NavigatorObserver {
-  final Map<T, RouteAware> _listeners = <T, RouteAware>{};
+  final Map<T, Set<RouteAware>> _listeners = <T, Set<RouteAware>>{};
 
   /// Subscribe [routeAware] to be informed about changes to [route].
   ///
@@ -1126,32 +1126,55 @@ class RouteObserver<T extends Route<dynamic>> extends NavigatorObserver {
   void subscribe(RouteAware routeAware, T route) {
     assert(routeAware != null);
     assert(route != null);
-    if (!_listeners.containsKey(route)) {
+    final Set<RouteAware> subscribers = _listeners.putIfAbsent(route, () => new Set<RouteAware>());
+    if (subscribers.add(routeAware)) {
       routeAware.didPush();
-      _listeners[route] = routeAware;
     }
   }
 
   /// Unsubscribe [routeAware].
   ///
-  /// [routeAware] is no longer informed about changes to its route.
+  /// [routeAware] is no longer informed about changes to its route. If the given argument was
+  /// subscribed to multiple types, this will unregister it (once) from each type.
   void unsubscribe(RouteAware routeAware) {
     assert(routeAware != null);
-    _listeners.remove(routeAware);
+    for (T route in _listeners.keys) {
+      final Set<RouteAware> subscribers = _listeners[route];
+      subscribers?.remove(routeAware);
+    }
   }
 
   @override
   void didPop(Route<dynamic> route, Route<dynamic> previousRoute) {
     if (route is T && previousRoute is T) {
-      _listeners[previousRoute]?.didPopNext();
-      _listeners[route]?.didPop();
+      final List<RouteAware> previousSubscribers = _listeners[previousRoute]?.toList();
+
+      if (previousSubscribers != null) {
+        for (RouteAware routeAware in previousSubscribers) {
+          routeAware.didPopNext();
+        }
+      }
+
+      final List<RouteAware> subscribers = _listeners[route]?.toList();
+
+      if (subscribers != null) {
+        for (RouteAware routeAware in subscribers) {
+          routeAware.didPop();
+        }
+      }
     }
   }
 
   @override
   void didPush(Route<dynamic> route, Route<dynamic> previousRoute) {
     if (route is T && previousRoute is T) {
-      _listeners[previousRoute]?.didPushNext();
+      final Set<RouteAware> previousSubscribers = _listeners[previousRoute];
+
+      if (previousSubscribers != null) {
+        for (RouteAware routeAware in previousSubscribers) {
+          routeAware.didPushNext();
+        }
+      }
     }
   }
 }

packages/flutter/test/widgets/routes_test.dart

@@ -453,6 +453,31 @@ void main() {
       observer.didPop(route, pageRoute);
       verifyNoMoreInteractions(pageRouteAware);
     });
+
+    test('does not call listeners when already subscribed', () {
+      final RouteObserver<PageRoute<dynamic>> observer = new RouteObserver<PageRoute<dynamic>>();
+      final RouteAware pageRouteAware = new MockRouteAware();
+      final MockPageRoute pageRoute = new MockPageRoute();
+      observer.subscribe(pageRouteAware, pageRoute);
+      observer.subscribe(pageRouteAware, pageRoute);
+      verify(pageRouteAware.didPush()).called(1);
+    });
+
+    test('does not call listeners when unsubscribed', () {
+      final RouteObserver<PageRoute<dynamic>> observer = new RouteObserver<PageRoute<dynamic>>();
+      final RouteAware pageRouteAware = new MockRouteAware();
+      final MockPageRoute pageRoute = new MockPageRoute();
+      final MockPageRoute nextPageRoute = new MockPageRoute();
+      observer.subscribe(pageRouteAware, pageRoute);
+      observer.subscribe(pageRouteAware, nextPageRoute);
+      verify(pageRouteAware.didPush()).called(2);
+
+      observer.unsubscribe(pageRouteAware);
+
+      observer.didPush(nextPageRoute, pageRoute);
+      observer.didPop(nextPageRoute, pageRoute);
+      verifyNoMoreInteractions(pageRouteAware);
+    });
   });
 }