Update PopupMenuButton widget (#80420)

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

@@ -732,6 +732,8 @@ class _PopupMenuRoute<T> extends PopupRoute<T> {
     this.shape,
     this.color,
     required this.capturedThemes,
+    this.menuKey,
+    this.positionCallback,
   }) : itemSizes = List<Size?>.filled(items.length, null);
 
   final RelativeRect position;
@@ -743,6 +745,8 @@ class _PopupMenuRoute<T> extends PopupRoute<T> {
   final ShapeBorder? shape;
   final Color? color;
   final CapturedThemes capturedThemes;
+  final Key? menuKey;
+  final PopupMenuButtonPositionCallback? positionCallback;
 
   @override
   Animation<double> createAnimation() {
@@ -778,12 +782,13 @@ class _PopupMenuRoute<T> extends PopupRoute<T> {
 
     final Widget menu = _PopupMenu<T>(route: this, semanticLabel: semanticLabel);
 
-    return Builder(
-      builder: (BuildContext context) {
+    return StatefulBuilder(
+      key: menuKey,
+      builder: (BuildContext context, StateSetter setState) {
         final MediaQueryData mediaQuery = MediaQuery.of(context);
         return CustomSingleChildLayout(
           delegate: _PopupMenuRouteLayout(
-            position,
+            positionCallback == null ? position : positionCallback!(),
             itemSizes,
             selectedItemIndex,
             Directionality.of(context),
@@ -801,6 +806,10 @@ class _PopupMenuRoute<T> extends PopupRoute<T> {
 ///
 /// `items` should be non-null and not empty.
 ///
+/// Prefer to use `positionCallback` to obtain position instead of 'position'
+/// when `positionCallback` is non-null. In this way, the position of the menu
+/// can be recalculated through this callback during the rebuild phase of the menu.
+///
 /// If `initialValue` is specified then the first item with a matching value
 /// will be highlighted and the value of `position` gives the rectangle whose
 /// vertical center will be aligned with the vertical center of the highlighted
@@ -862,6 +871,8 @@ Future<T?> showMenu<T>({
   ShapeBorder? shape,
   Color? color,
   bool useRootNavigator = false,
+  Key? menuKey,
+  PopupMenuButtonPositionCallback? positionCallback,
 }) {
   assert(context != null);
   assert(position != null);
@@ -891,6 +902,8 @@ Future<T?> showMenu<T>({
     shape: shape,
     color: color,
     capturedThemes: InheritedTheme.capture(from: context, to: navigator.context),
+    menuKey: menuKey,
+    positionCallback: positionCallback,
   ));
 }
 
@@ -1090,11 +1103,44 @@ class PopupMenuButton<T> extends StatefulWidget {
   PopupMenuButtonState<T> createState() => PopupMenuButtonState<T>();
 }
 
+/// Signature for the callback used by [showMenu] to obtain the position of the
+/// [PopupMenuButton].
+///
+/// Used by [showMenu].
+typedef PopupMenuButtonPositionCallback = RelativeRect Function();
+
 /// The [State] for a [PopupMenuButton].
 ///
 /// See [showButtonMenu] for a way to programmatically open the popup menu
 /// of your button state.
 class PopupMenuButtonState<T> extends State<PopupMenuButton<T>> {
+  GlobalKey _menuGlobalKey = GlobalKey();
+  RelativeRect? _buttonPosition;
+
+  RelativeRect _getButtonPosition() => _buttonPosition!;
+
+  RelativeRect _calculateButtonPosition() {
+    final RenderBox button = context.findRenderObject()! as RenderBox;
+    final RenderBox overlay = Navigator.of(context).overlay!.context.findRenderObject()! as RenderBox;
+    return RelativeRect.fromRect(
+      Rect.fromPoints(
+        button.localToGlobal(widget.offset, ancestor: overlay),
+        button.localToGlobal(button.size.bottomRight(Offset.zero) + widget.offset, ancestor: overlay),
+      ),
+      Offset.zero & overlay.size,
+    );
+  }
+
+  void _maybeUpdateMenuPosition() {
+    WidgetsBinding.instance!.addPostFrameCallback((Duration duration) {
+      final RelativeRect newPosition = _calculateButtonPosition();
+      if (newPosition != _buttonPosition) {
+        _menuGlobalKey.currentState?.setState(() {});
+        _buttonPosition = newPosition;
+      }
+    });
+  }
+
   /// A method to show a popup menu with the items supplied to
   /// [PopupMenuButton.itemBuilder] at the position of your [PopupMenuButton].
   ///
@@ -1105,16 +1151,12 @@ class PopupMenuButtonState<T> extends State<PopupMenuButton<T>> {
   /// show the menu of the button with `globalKey.currentState.showButtonMenu`.
   void showButtonMenu() {
     final PopupMenuThemeData popupMenuTheme = PopupMenuTheme.of(context);
-    final RenderBox button = context.findRenderObject()! as RenderBox;
-    final RenderBox overlay = Navigator.of(context).overlay!.context.findRenderObject()! as RenderBox;
-    final RelativeRect position = RelativeRect.fromRect(
-      Rect.fromPoints(
-        button.localToGlobal(widget.offset, ancestor: overlay),
-        button.localToGlobal(button.size.bottomRight(Offset.zero) + widget.offset, ancestor: overlay),
-      ),
-      Offset.zero & overlay.size,
-    );
     final List<PopupMenuEntry<T>> items = widget.itemBuilder(context);
+    // It is possible that the fade-out animation of the menu has not finished
+    // yet, and the key needs to be regenerated at this time, otherwise there will
+    // be an exception of duplicate GlobalKey.
+    if (_menuGlobalKey.currentState != null)
+      _menuGlobalKey = GlobalKey();
     // Only show the menu if there is something to show
     if (items.isNotEmpty) {
       showMenu<T?>(
@@ -1122,9 +1164,11 @@ class PopupMenuButtonState<T> extends State<PopupMenuButton<T>> {
         elevation: widget.elevation ?? popupMenuTheme.elevation,
         items: items,
         initialValue: widget.initialValue,
-        position: position,
+        position: _buttonPosition!,
         shape: widget.shape ?? popupMenuTheme.shape,
         color: widget.color ?? popupMenuTheme.color,
+        menuKey: _menuGlobalKey,
+        positionCallback: _getButtonPosition,
       )
       .then<void>((T? newValue) {
         if (!mounted)
@@ -1148,6 +1192,18 @@ class PopupMenuButtonState<T> extends State<PopupMenuButton<T>> {
     }
   }
 
+  @override
+  void didUpdateWidget(PopupMenuButton<T> oldWidget) {
+    _maybeUpdateMenuPosition();
+    super.didUpdateWidget(oldWidget);
+  }
+
+  @override
+  void didChangeDependencies() {
+    _maybeUpdateMenuPosition();
+    super.didChangeDependencies();
+  }
+
   @override
   Widget build(BuildContext context) {
     final bool enableFeedback = widget.enableFeedback

packages/flutter/test/material/popup_menu_test.dart

@@ -2209,6 +2209,87 @@ void main() {
     await tester.pumpAndSettle();
     expect(find.text('foo'), findsOneWidget);
   });
+
+  testWidgets('The opened menu should follow if the button\'s position changed', (WidgetTester tester) async {
+    final GlobalKey buttonKey = GlobalKey();
+
+    Widget buildFrame(double width, double height) {
+      return MaterialApp(
+        home: Scaffold(
+          body:  SizedBox(
+            height: height,
+            width: width,
+            child: Center(
+              child: PopupMenuButton<int>(
+                child: SizedBox(
+                  key: buttonKey,
+                  height: 10.0,
+                  width: 10.0,
+                  child: const ColoredBox(
+                    color: Colors.pink,
+                  ),
+                ),
+                itemBuilder: (BuildContext context) => <PopupMenuEntry<int>>[
+                  const PopupMenuItem<int>(child: Text('-1-'), value: 1),
+                  const PopupMenuItem<int>(child: Text('-2-'), value: 2),
+                ],
+              ),
+            ),
+          ),
+        ),
+      );
+    }
+
+    await tester.pumpWidget(buildFrame(100.0, 100.0));
+
+    // Open the menu.
+    await tester.tap(find.byKey(buttonKey));
+    await tester.pumpAndSettle();
+
+    //                 +--------+--------+ 100
+    //                 |        |        |
+    //                 |        | (50,50)|
+    //                 +--------+--------+
+    //                 |        |        |
+    //                 |        |        |
+    //             100 +--------+--------+
+    //
+    // The button is a rectangle of 10 * 10 size and is centered,
+    // so its top-left offset should be (45.0, 45.0).
+    Offset buttonOffset = tester.getTopLeft(find.byKey(buttonKey));
+    expect(buttonOffset, const Offset(45.0, 45.0));
+
+    // The top-left corner of the menu and button should be aligned.
+    Offset popupMenuOffset = tester.getTopLeft(find.byType(SingleChildScrollView));
+    expect(popupMenuOffset, buttonOffset);
+
+    // Keep the menu opened and re-layout the screen.
+    await tester.pumpWidget(buildFrame(200.0, 300.0));
+
+    //                 +-----------+-----------+ 200
+    //                 |           |           |
+    //                 |           |           |
+    //                 |           |           |
+    //                 |           |           |
+    //                 |           | (100,150) |
+    //                 +-----------+-----------+
+    //                 |           |           |
+    //                 |           |           |
+    //                 |           |           |
+    //                 |           |           |
+    //                 |           |           |
+    //             300 +-----------+-----------+
+    //
+    // The button is a rectangle of 10 * 10 size and is centered,
+    // so its top-left offset should be (95.0, 145.0).
+    await tester.pump(); // Need a frame to update the menu.
+    buttonOffset = tester.getTopLeft(find.byKey(buttonKey));
+    expect(buttonOffset, const Offset(95.0, 145.0));
+
+    // The popup menu should follow the button.
+    popupMenuOffset = tester.getTopLeft(find.byType(SingleChildScrollView));
+    expect(popupMenuOffset, buttonOffset);
+  });
 }
 
 class TestApp extends StatefulWidget {