Fix Backbutton is not displayed when there is a endDrawer (#102093)

Author: chunhtai

packages/flutter/lib/src/material/app_bar.dart

@@ -862,7 +862,6 @@ class _AppBarState extends State<AppBar> {
 
     final bool hasDrawer = scaffold?.hasDrawer ?? false;
     final bool hasEndDrawer = scaffold?.hasEndDrawer ?? false;
-    final bool canPop = parentRoute?.canPop ?? false;
     final bool useCloseButton = parentRoute is PageRoute<dynamic> && parentRoute.fullscreenDialog;
 
     final double toolbarHeight = widget.toolbarHeight ?? appBarTheme.toolbarHeight ?? kToolbarHeight;
@@ -948,9 +947,8 @@ class _AppBarState extends State<AppBar> {
           onPressed: _handleDrawerButton,
           tooltip: MaterialLocalizations.of(context).openAppDrawerTooltip,
         );
-      } else {
-        if (!hasEndDrawer && canPop)
-          leading = useCloseButton ? const CloseButton() : const BackButton();
+      } else if (parentRoute?.impliesAppBarDismissal ?? false) {
+        leading = useCloseButton ? const CloseButton() : const BackButton();
       }
     }
     if (leading != null) {

packages/flutter/lib/src/material/drawer.dart

@@ -401,7 +401,7 @@ class DrawerControllerState extends State<DrawerController> with SingleTickerPro
     if (_historyEntry == null) {
       final ModalRoute<dynamic>? route = ModalRoute.of(context);
       if (route != null) {
-        _historyEntry = LocalHistoryEntry(onRemove: _handleHistoryEntryRemoved);
+        _historyEntry = LocalHistoryEntry(onRemove: _handleHistoryEntryRemoved, impliesAppBarDismissal: false);
         route.addLocalHistoryEntry(_historyEntry!);
         FocusScope.of(context).setFirstFocus(_focusScopeNode);
       }

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

@@ -455,13 +455,21 @@ abstract class TransitionRoute<T> extends OverlayRoute<T> {
 /// An entry in the history of a [LocalHistoryRoute].
 class LocalHistoryEntry {
   /// Creates an entry in the history of a [LocalHistoryRoute].
-  LocalHistoryEntry({ this.onRemove });
+  ///
+  /// The [impliesAppBarDismissal] defaults to true if not provided.
+  LocalHistoryEntry({ this.onRemove, this.impliesAppBarDismissal = true });
 
   /// Called when this entry is removed from the history of its associated [LocalHistoryRoute].
   final VoidCallback? onRemove;
 
   LocalHistoryRoute<dynamic>? _owner;
 
+  /// Whether an [AppBar] in the route this entry belongs to should
+  /// automatically add a back button or close button.
+  ///
+  /// Defaults to true.
+  final bool impliesAppBarDismissal;
+
   /// Remove this entry from the history of its associated [LocalHistoryRoute].
   void remove() {
     _owner?.removeLocalHistoryEntry(this);
@@ -482,7 +490,7 @@ class LocalHistoryEntry {
 /// is removed from the list and its [LocalHistoryEntry.onRemove] is called.
 mixin LocalHistoryRoute<T> on Route<T> {
   List<LocalHistoryEntry>? _localHistory;
-
+  int _entriesImpliesAppBarDismissal = 0;
   /// Adds a local history entry to this route.
   ///
   /// When asked to pop, if this route has any local history entries, this route
@@ -620,7 +628,12 @@ mixin LocalHistoryRoute<T> on Route<T> {
     _localHistory ??= <LocalHistoryEntry>[];
     final bool wasEmpty = _localHistory!.isEmpty;
     _localHistory!.add(entry);
-    if (wasEmpty)
+    bool internalStateChanged = false;
+    if (entry.impliesAppBarDismissal) {
+      internalStateChanged = _entriesImpliesAppBarDismissal == 0;
+      _entriesImpliesAppBarDismissal += 1;
+    }
+    if (wasEmpty || internalStateChanged)
       changedInternalState();
   }
 
@@ -632,10 +645,15 @@ mixin LocalHistoryRoute<T> on Route<T> {
     assert(entry != null);
     assert(entry._owner == this);
     assert(_localHistory!.contains(entry));
-    _localHistory!.remove(entry);
+    bool internalStateChanged = false;
+    if (_localHistory!.remove(entry) && entry.impliesAppBarDismissal) {
+      _entriesImpliesAppBarDismissal -= 1;
+      internalStateChanged = _entriesImpliesAppBarDismissal == 0;
+    }
     entry._owner = null;
     entry._notifyRemoved();
-    if (_localHistory!.isEmpty) {
+    if (_localHistory!.isEmpty || internalStateChanged) {
+      assert(_entriesImpliesAppBarDismissal == 0);
       if (SchedulerBinding.instance.schedulerPhase == SchedulerPhase.persistentCallbacks) {
         // The local history might be removed as a result of disposing inactive
         // elements during finalizeTree. The state is locked at this moment, and
@@ -663,7 +681,12 @@ mixin LocalHistoryRoute<T> on Route<T> {
       assert(entry._owner == this);
       entry._owner = null;
       entry._notifyRemoved();
-      if (_localHistory!.isEmpty)
+      bool internalStateChanged = false;
+      if (entry.impliesAppBarDismissal) {
+        _entriesImpliesAppBarDismissal -= 1;
+        internalStateChanged = _entriesImpliesAppBarDismissal == 0;
+      }
+      if (_localHistory!.isEmpty || internalStateChanged)
         changedInternalState();
       return false;
     }
@@ -697,6 +720,7 @@ class _ModalScopeStatus extends InheritedWidget {
   const _ModalScopeStatus({
     required this.isCurrent,
     required this.canPop,
+    required this.impliesAppBarDismissal,
     required this.route,
     required super.child,
   }) : assert(isCurrent != null),
@@ -706,12 +730,14 @@ class _ModalScopeStatus extends InheritedWidget {
 
   final bool isCurrent;
   final bool canPop;
+  final bool impliesAppBarDismissal;
   final Route<dynamic> route;
 
   @override
   bool updateShouldNotify(_ModalScopeStatus old) {
     return isCurrent != old.isCurrent ||
            canPop != old.canPop ||
+           impliesAppBarDismissal != old.impliesAppBarDismissal ||
            route != old.route;
   }
 
@@ -720,6 +746,7 @@ class _ModalScopeStatus extends InheritedWidget {
     super.debugFillProperties(description);
     description.add(FlagProperty('isCurrent', value: isCurrent, ifTrue: 'active', ifFalse: 'inactive'));
     description.add(FlagProperty('canPop', value: canPop, ifTrue: 'can pop'));
+    description.add(FlagProperty('impliesAppBarDismissal', value: impliesAppBarDismissal, ifTrue: 'implies app bar dismissal'));
   }
 }
 
@@ -822,6 +849,7 @@ class _ModalScopeState<T> extends State<_ModalScope<T>> {
         route: widget.route,
         isCurrent: widget.route.isCurrent, // _routeSetState is called if this updates
         canPop: widget.route.canPop, // _routeSetState is called if this updates
+        impliesAppBarDismissal: widget.route.impliesAppBarDismissal,
         child: Offstage(
           offstage: widget.route.offstage, // _routeSetState is called if this updates
           child: PageStorage(
@@ -1561,6 +1589,14 @@ abstract class ModalRoute<T> extends TransitionRoute<T> with LocalHistoryRoute<T
   /// notified.
   bool get canPop => hasActiveRouteBelow || willHandlePopInternally;
 
+  /// Whether an [AppBar] in the route should automatically add a back button or
+  /// close button.
+  ///
+  /// This getter returns true if there is at least one active route below it,
+  /// or there is at least one [LocalHistoryEntry] with `impliesAppBarDismissal`
+  /// set to true
+  bool get impliesAppBarDismissal => hasActiveRouteBelow || _entriesImpliesAppBarDismissal > 0;
+
   // Internals
 
   final GlobalKey<_ModalScopeState<T>> _scopeKey = GlobalKey<_ModalScopeState<T>>();

packages/flutter/test/material/app_bar_test.dart

@@ -3074,6 +3074,44 @@ void main() {
     });
   });
 
+  // Regression test for https://github.com/flutter/flutter/issues/80256
+  testWidgets('The second page should have a back button even it has a end drawer', (WidgetTester tester) async {
+    final Page<void> page1 = MaterialPage<void>(
+        key: const ValueKey<String>('1'),
+        child: Scaffold(
+          key: const ValueKey<String>('1'),
+          appBar: AppBar(),
+          endDrawer: const Drawer(),
+        )
+    );
+    final Page<void> page2 = MaterialPage<void>(
+        key: const ValueKey<String>('2'),
+        child: Scaffold(
+          key: const ValueKey<String>('2'),
+          appBar: AppBar(),
+          endDrawer: const Drawer(),
+        )
+    );
+    final List<Page<void>> pages = <Page<void>>[ page1, page2 ];
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Navigator(
+          pages: pages,
+          onPopPage: (Route<Object?> route, Object? result) => false,
+        ),
+      ),
+    );
+
+    // The page2 should have a back button.
+    expect(
+        find.descendant(
+          of: find.byKey(const ValueKey<String>('2')),
+          matching: find.byType(BackButton),
+        ),
+        findsOneWidget
+    );
+  });
+
   testWidgets('AppBar.preferredHeightFor', (WidgetTester tester) async {
     late double preferredHeight;
     late Size preferredSize;