Build routes even less. (#58202)

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

@@ -185,7 +185,6 @@ abstract class TransitionRoute<T> extends OverlayRoute<T> {
         }
         break;
     }
-    changedInternalState();
   }
 
   @override
@@ -193,16 +192,19 @@ abstract class TransitionRoute<T> extends OverlayRoute<T> {
     assert(!_transitionCompleter.isCompleted, 'Cannot install a $runtimeType after disposing it.');
     _controller = createAnimationController();
     assert(_controller != null, '$runtimeType.createAnimationController() returned null.');
-    _animation = createAnimation();
+    _animation = createAnimation()
+      ..addStatusListener(_handleStatusChanged);
     assert(_animation != null, '$runtimeType.createAnimation() returned null.');
     super.install();
+    if (_animation.isCompleted && overlayEntries.isNotEmpty) {
+      overlayEntries.first.opaque = opaque;
+    }
   }
 
   @override
   TickerFuture didPush() {
     assert(_controller != null, '$runtimeType.didPush called before calling install() or after calling dispose().');
     assert(!_transitionCompleter.isCompleted, 'Cannot reuse a $runtimeType after disposing it.');
-    _didPushOrReplace();
     super.didPush();
     return _controller.forward();
   }
@@ -211,7 +213,6 @@ abstract class TransitionRoute<T> extends OverlayRoute<T> {
   void didAdd() {
     assert(_controller != null, '$runtimeType.didPush called before calling install() or after calling dispose().');
     assert(!_transitionCompleter.isCompleted, 'Cannot reuse a $runtimeType after disposing it.');
-    _didPushOrReplace();
     super.didAdd();
     _controller.value = _controller.upperBound;
   }
@@ -222,19 +223,9 @@ abstract class TransitionRoute<T> extends OverlayRoute<T> {
     assert(!_transitionCompleter.isCompleted, 'Cannot reuse a $runtimeType after disposing it.');
     if (oldRoute is TransitionRoute)
       _controller.value = oldRoute._controller.value;
-    _didPushOrReplace();
     super.didReplace(oldRoute);
   }
 
-  void _didPushOrReplace() {
-    _animation.addStatusListener(_handleStatusChanged);
-    // If the animation is already completed, _handleStatusChanged will not get
-    // a chance to set opaqueness of OverlayEntry.
-    if (_animation.isCompleted && overlayEntries.isNotEmpty) {
-      overlayEntries.first.opaque = opaque;
-    }
-  }
-
   @override
   bool didPop(T result) {
     assert(_controller != null, '$runtimeType.didPop called before calling install() or after calling dispose().');
@@ -856,7 +847,7 @@ abstract class ModalRoute<T> extends TransitionRoute<T> with LocalHistoryRoute<T
   /// ```
   ///
   /// The given [BuildContext] will be rebuilt if the state of the route changes
-  /// (specifically, if [isCurrent] or [canPop] change value).
+  /// while it is visible (specifically, if [isCurrent] or [canPop] change value).
   @optionalTypeArgs
   static ModalRoute<T> of<T extends Object>(BuildContext context) {
     final _ModalScopeStatus widget = context.dependOnInheritedWidgetOfExactType<_ModalScopeStatus>();
@@ -936,7 +927,8 @@ abstract class ModalRoute<T> extends TransitionRoute<T> with LocalHistoryRoute<T
   /// is not wrapped in any transition widgets.
   ///
   /// The [buildTransitions] method, in contrast to [buildPage], is called each
-  /// time the [Route]'s state changes (e.g. the value of [canPop]).
+  /// time the [Route]'s state changes while it is visible (e.g. if the value of
+  /// [canPop] changes on the active route).
   ///
   /// The [buildTransitions] method is typically used to define transitions
   /// that animate the new topmost route's comings and goings. When the
@@ -1392,8 +1384,9 @@ abstract class ModalRoute<T> extends TransitionRoute<T> with LocalHistoryRoute<T
 
   /// Whether this route can be popped.
   ///
-  /// When this changes, the route will rebuild, and any widgets that used
-  /// [ModalRoute.of] will be notified.
+  /// When this changes, if the route is visible, the route will
+  /// rebuild, and any widgets that used [ModalRoute.of] will be
+  /// notified.
   bool get canPop => !isFirst || willHandlePopInternally;
 
   // Internals

packages/flutter/test/widgets/navigator_test.dart

@@ -1182,7 +1182,50 @@ void main() {
     expect(log, <String>['building B', 'building C', 'found C', 'building D']);
     key.currentState.pop<void>();
     await tester.pumpAndSettle(const Duration(milliseconds: 10));
-    expect(log, <String>['building B', 'building C', 'found C', 'building D', 'building C', 'found C']);
+    expect(log, <String>['building B', 'building C', 'found C', 'building D']);
+  });
+
+  testWidgets('Routes don\'t rebuild just because their animations ended', (WidgetTester tester) async {
+    final GlobalKey<NavigatorState> key = GlobalKey<NavigatorState>();
+    final List<String> log = <String>[];
+    Route<dynamic> nextRoute = PageRouteBuilder<int>(
+      pageBuilder: (BuildContext context, Animation<double> animation, Animation<double> secondaryAnimation) {
+        log.add('building page 1 - ${ModalRoute.of(context).canPop}');
+        return const Placeholder();
+      },
+    );
+    await tester.pumpWidget(MaterialApp(
+      navigatorKey: key,
+      onGenerateRoute: (RouteSettings settings) {
+        assert(nextRoute != null);
+        final Route<dynamic> result = nextRoute;
+        nextRoute = null;
+        return result;
+      },
+    ));
+    expect(log, <String>['building page 1 - false']);
+    key.currentState.pushReplacement(PageRouteBuilder<int>(
+      pageBuilder: (BuildContext context, Animation<double> animation, Animation<double> secondaryAnimation) {
+        log.add('building page 2 - ${ModalRoute.of(context).canPop}');
+        return const Placeholder();
+      },
+    ));
+    expect(log, <String>['building page 1 - false']);
+    await tester.pump();
+    expect(log, <String>['building page 1 - false', 'building page 2 - false']);
+    await tester.pump(const Duration(milliseconds: 150));
+    expect(log, <String>['building page 1 - false', 'building page 2 - false']);
+    key.currentState.pushReplacement(PageRouteBuilder<int>(
+      pageBuilder: (BuildContext context, Animation<double> animation, Animation<double> secondaryAnimation) {
+        log.add('building page 3 - ${ModalRoute.of(context).canPop}');
+        return const Placeholder();
+      },
+    ));
+    expect(log, <String>['building page 1 - false', 'building page 2 - false']);
+    await tester.pump();
+    expect(log, <String>['building page 1 - false', 'building page 2 - false', 'building page 3 - false']);
+    await tester.pump(const Duration(milliseconds: 200));
+    expect(log, <String>['building page 1 - false', 'building page 2 - false', 'building page 3 - false']);
   });
 
   testWidgets('route semantics', (WidgetTester tester) async {