fixes route name annoucement in navigator (#50495)

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

@@ -77,18 +77,6 @@ enum RoutePopDisposition {
   bubble,
 }
 
-/// Name for the method which is used for sending messages from framework to
-/// engine after a route is popped.
-const String _routePoppedMethod = 'routePopped';
-
-/// Name for the method which is used for sending messages from framework to
-/// engine after a route is pushed.
-const String _routePushedMethod = 'routePushed';
-
-/// Name for the method which is used for sending messages from framework to
-/// engine after a route is replaced.
-const String _routeReplacedMethod = 'routeReplaced';
-
 /// An abstraction for an entry managed by a [Navigator].
 ///
 /// This class defines an abstract interface between the navigator and the
@@ -1793,7 +1781,6 @@ class _RouteEntry {
     if (isNewFirst) {
       route.didChangeNext(null);
     }
-    RouteNotificationMessages.maybeNotifyRouteChange(_routePushedMethod, route, previous);
     for (final NavigatorObserver observer in navigator.widget.observers)
       observer.didPush(route, previousPresent);
   }
@@ -1829,12 +1816,10 @@ class _RouteEntry {
     }
 
     if (previousState == _RouteLifecycle.replace || previousState == _RouteLifecycle.pushReplace) {
-      RouteNotificationMessages.maybeNotifyRouteChange(_routeReplacedMethod, route, previous);
       for (final NavigatorObserver observer in navigator.widget.observers)
         observer.didReplace(newRoute: route, oldRoute: previous);
     } else {
       assert(previousState == _RouteLifecycle.push);
-      RouteNotificationMessages.maybeNotifyRouteChange(_routePushedMethod, route, previous);
       for (final NavigatorObserver observer in navigator.widget.observers)
         observer.didPush(route, previousPresent);
     }
@@ -1852,11 +1837,6 @@ class _RouteEntry {
     currentState = _RouteLifecycle.popping;
     for (final NavigatorObserver observer in navigator.widget.observers)
       observer.didPop(route, previousPresent);
-    RouteNotificationMessages.maybeNotifyRouteChange(
-      _routePoppedMethod,
-      route,
-      previousPresent,
-    );
   }
 
   void handleRemoval({ @required NavigatorState navigator, @required Route<dynamic> previousPresent }) {
@@ -2009,6 +1989,8 @@ class NavigatorState extends State<Navigator> with TickerProviderStateMixin {
       yield* entry.route.overlayEntries;
   }
 
+  String _lastAnnouncedRouteName;
+
   void _flushHistoryUpdates({bool rearrangeOverlay = true}) {
     assert(_debugLocked);
     // Clean up the list, sending updates to the routes that changed. Notably,
@@ -2117,6 +2099,14 @@ class NavigatorState extends State<Navigator> with TickerProviderStateMixin {
     // notifications.
     _flushRouteAnnouncement();
 
+    // Announces route name changes.
+    final _RouteEntry lastEntry = _history.lastWhere(_RouteEntry.isPresentPredicate, orElse: () => null);
+    final String routeName = lastEntry?.route?.settings?.name;
+    if (routeName != _lastAnnouncedRouteName) {
+      RouteNotificationMessages.maybeNotifyRouteChange(routeName, _lastAnnouncedRouteName);
+      _lastAnnouncedRouteName = routeName;
+    }
+
     // Lastly, removes the overlay entries of all marked entries and disposes
     // them.
     for (final _RouteEntry entry in toBeDisposed) {

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

@@ -5,19 +5,17 @@
 import 'package:flutter/foundation.dart';
 import 'package:flutter/services.dart';
 
-import 'navigator.dart';
-
 /// Messages for route change notifications.
 class RouteNotificationMessages {
-  // This class is not meant to be instatiated or extended; this constructor
+  // This class is not meant to be instantiated or extended; this constructor
   // prevents instantiation and extension.
   // ignore: unused_element
   RouteNotificationMessages._();
 
   /// When the engine is Web notify the platform for a route change.
-  static void maybeNotifyRouteChange(String methodName, Route<dynamic> route, Route<dynamic> previousRoute) {
+  static void maybeNotifyRouteChange(String routeName, String previousRouteName) {
     if(kIsWeb) {
-      _notifyRouteChange(methodName, route, previousRoute);
+      _notifyRouteChange(routeName, previousRouteName);
     } else {
       // No op.
     }
@@ -25,17 +23,13 @@ class RouteNotificationMessages {
 
   /// Notifies the platform of a route change.
   ///
-  /// There are three methods: 'routePushed', 'routePopped', 'routeReplaced'.
-  ///
   /// See also:
   ///
   ///  * [SystemChannels.navigation], which handles subsequent navigation
   ///    requests.
-  static void _notifyRouteChange(String methodName, Route<dynamic> route, Route<dynamic> previousRoute) {
-    final String previousRouteName = previousRoute?.settings?.name;
-    final String routeName = route?.settings?.name;
+  static void _notifyRouteChange(String routeName, String previousRouteName) {
     SystemChannels.navigation.invokeMethod<void>(
-      methodName,
+      'routeUpdated',
       <String, dynamic>{
         'previousRouteName': previousRouteName,
         'routeName': routeName,

packages/flutter/test/widgets/route_notification_messages_test.dart

@@ -63,7 +63,7 @@ void main() {
     expect(
         log.last,
         isMethodCall(
-          'routePushed',
+          'routeUpdated',
           arguments: <String, dynamic>{
             'previousRouteName': null,
             'routeName': '/',
@@ -78,7 +78,7 @@ void main() {
     expect(
         log.last,
         isMethodCall(
-          'routePushed',
+          'routeUpdated',
           arguments: <String, dynamic>{
             'previousRouteName': '/',
             'routeName': '/A',
@@ -93,10 +93,10 @@ void main() {
     expect(
         log.last,
         isMethodCall(
-          'routePopped',
+          'routeUpdated',
           arguments: <String, dynamic>{
-            'previousRouteName': '/',
-            'routeName': '/A',
+            'previousRouteName': '/A',
+            'routeName': '/',
           },
         ));
   });
@@ -130,7 +130,7 @@ void main() {
     expect(
         log.last,
         isMethodCall(
-          'routePushed',
+          'routeUpdated',
           arguments: <String, dynamic>{
             'previousRouteName': null,
             'routeName': '/',
@@ -145,7 +145,7 @@ void main() {
     expect(
         log.last,
         isMethodCall(
-          'routePushed',
+          'routeUpdated',
           arguments: <String, dynamic>{
             'previousRouteName': '/',
             'routeName': '/A',
@@ -160,7 +160,7 @@ void main() {
     expect(
         log.last,
         isMethodCall(
-          'routeReplaced',
+          'routeUpdated',
           arguments: <String, dynamic>{
             'previousRouteName': '/A',
             'routeName': '/B',
@@ -195,7 +195,7 @@ void main() {
     expect(log, hasLength(1));
     expect(
       log.last,
-      isMethodCall('routePushed', arguments: <String, dynamic>{
+      isMethodCall('routeUpdated', arguments: <String, dynamic>{
         'previousRouteName': null,
         'routeName': '/home',
       }),
@@ -208,7 +208,7 @@ void main() {
     expect(log, hasLength(2));
     expect(
       log.last,
-      isMethodCall('routePushed', arguments: <String, dynamic>{
+      isMethodCall('routeUpdated', arguments: <String, dynamic>{
         'previousRouteName': '/home',
         'routeName': null,
       }),