Adds `PopupMenuPosition position` to the `PopupMenuThemeData` (#110268)

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

@@ -38,14 +38,6 @@ const double _kMenuVerticalPadding = 8.0;
 const double _kMenuWidthStep = 56.0;
 const double _kMenuScreenPadding = 8.0;
 
-/// Used to configure how the [PopupMenuButton] positions its popup menu.
-enum PopupMenuPosition {
-  /// Menu is positioned over the anchor.
-  over,
-  /// Menu is positioned under the anchor.
-  under,
-}
-
 /// A base class for entries in a Material Design popup menu.
 ///
 /// The popup menu widget uses this interface to interact with the menu items.
@@ -1025,7 +1017,7 @@ class PopupMenuButton<T> extends StatefulWidget {
     this.color,
     this.enableFeedback,
     this.constraints,
-    this.position = PopupMenuPosition.over,
+    this.position,
     this.clipBehavior = Clip.none,
   }) : assert(itemBuilder != null),
        assert(enabled != null),
@@ -1157,9 +1149,11 @@ class PopupMenuButton<T> extends StatefulWidget {
   /// [offset] is used to change the position of the popup menu relative to the
   /// position set by this parameter.
   ///
-  /// When not set, the position defaults to [PopupMenuPosition.over] which makes the
-  /// popup menu appear directly over the button that was used to create it.
-  final PopupMenuPosition position;
+  /// If this property is `null`, then [PopupMenuThemeData.position] is used. If
+  /// [PopupMenuThemeData.position] is also `null`, then the position defaults
+  /// to [PopupMenuPosition.over] which makes the popup menu appear directly
+  /// over the button that was used to create it.
+  final PopupMenuPosition? position;
 
   /// {@macro flutter.material.Material.clipBehavior}
   ///
@@ -1189,8 +1183,9 @@ class PopupMenuButtonState<T> extends State<PopupMenuButton<T>> {
     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 PopupMenuPosition popupMenuPosition = widget.position ?? popupMenuTheme.position ?? PopupMenuPosition.over;
     final Offset offset;
-    switch (widget.position) {
+    switch (popupMenuPosition) {
       case PopupMenuPosition.over:
         offset = widget.offset;
         break;

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

@@ -13,6 +13,14 @@ import 'theme.dart';
 // Examples can assume:
 // late BuildContext context;
 
+/// Used to configure how the [PopupMenuButton] positions its popup menu.
+enum PopupMenuPosition {
+  /// Menu is positioned over the anchor.
+  over,
+  /// Menu is positioned under the anchor.
+  under,
+}
+
 /// Defines the visual properties of the routes used to display popup menus
 /// as well as [PopupMenuItem] and [PopupMenuDivider] widgets.
 ///
@@ -43,6 +51,7 @@ class PopupMenuThemeData with Diagnosticable {
     this.textStyle,
     this.enableFeedback,
     this.mouseCursor,
+    this.position,
   });
 
   /// The background color of the popup menu.
@@ -67,6 +76,12 @@ class PopupMenuThemeData with Diagnosticable {
   /// If specified, overrides the default value of [PopupMenuItem.mouseCursor].
   final MaterialStateProperty<MouseCursor?>? mouseCursor;
 
+  /// Whether the popup menu is positioned over or under the popup menu button.
+  ///
+  /// When not set, the position defaults to [PopupMenuPosition.over] which makes the
+  /// popup menu appear directly over the button that was used to create it.
+  final PopupMenuPosition? position;
+
   /// Creates a copy of this object with the given fields replaced with the
   /// new values.
   PopupMenuThemeData copyWith({
@@ -76,6 +91,7 @@ class PopupMenuThemeData with Diagnosticable {
     TextStyle? textStyle,
     bool? enableFeedback,
     MaterialStateProperty<MouseCursor?>? mouseCursor,
+    PopupMenuPosition? position,
   }) {
     return PopupMenuThemeData(
       color: color ?? this.color,
@@ -84,6 +100,7 @@ class PopupMenuThemeData with Diagnosticable {
       textStyle: textStyle ?? this.textStyle,
       enableFeedback: enableFeedback ?? this.enableFeedback,
       mouseCursor: mouseCursor ?? this.mouseCursor,
+      position: position ?? this.position,
     );
   }
 
@@ -104,6 +121,7 @@ class PopupMenuThemeData with Diagnosticable {
       textStyle: TextStyle.lerp(a?.textStyle, b?.textStyle, t),
       enableFeedback: t < 0.5 ? a?.enableFeedback : b?.enableFeedback,
       mouseCursor: t < 0.5 ? a?.mouseCursor : b?.mouseCursor,
+      position: t < 0.5 ? a?.position : b?.position,
     );
   }
 
@@ -115,6 +133,7 @@ class PopupMenuThemeData with Diagnosticable {
     textStyle,
     enableFeedback,
     mouseCursor,
+    position,
   );
 
   @override
@@ -131,7 +150,8 @@ class PopupMenuThemeData with Diagnosticable {
         && other.shape == shape
         && other.textStyle == textStyle
         && other.enableFeedback == enableFeedback
-        && other.mouseCursor == mouseCursor;
+        && other.mouseCursor == mouseCursor
+        && other.position == position;
   }
 
   @override
@@ -143,6 +163,7 @@ class PopupMenuThemeData with Diagnosticable {
     properties.add(DiagnosticsProperty<TextStyle>('text style', textStyle, defaultValue: null));
     properties.add(DiagnosticsProperty<bool>('enableFeedback', enableFeedback, defaultValue: null));
     properties.add(DiagnosticsProperty<MaterialStateProperty<MouseCursor?>>('mouseCursor', mouseCursor, defaultValue: null));
+    properties.add(EnumProperty<PopupMenuPosition?>('position', position, defaultValue: null));
   }
 }
 

packages/flutter/test/material/popup_menu_theme_test.dart

@@ -13,6 +13,7 @@ PopupMenuThemeData _popupMenuTheme() {
     shape: BeveledRectangleBorder(borderRadius: BorderRadius.all(Radius.circular(12))),
     elevation: 12.0,
     textStyle: TextStyle(color: Color(0xffffffff), textBaseline: TextBaseline.alphabetic),
+    position: PopupMenuPosition.under,
   );
 }
 
@@ -29,6 +30,7 @@ void main() {
     expect(popupMenuTheme.elevation, null);
     expect(popupMenuTheme.textStyle, null);
     expect(popupMenuTheme.mouseCursor, null);
+    expect(popupMenuTheme.position, null);
   });
 
   testWidgets('Default PopupMenuThemeData debugFillProperties', (WidgetTester tester) async {
@@ -51,6 +53,7 @@ void main() {
       elevation: 2.0,
       textStyle: TextStyle(color: Color(0xffffffff)),
       mouseCursor: MaterialStateMouseCursor.clickable,
+      position: PopupMenuPosition.over,
     ).debugFillProperties(builder);
 
     final List<String> description = builder.properties
@@ -64,6 +67,7 @@ void main() {
       'elevation: 2.0',
       'text style: TextStyle(inherit: true, color: Color(0xffffffff))',
       'mouseCursor: MaterialStateMouseCursor(clickable)',
+      'position: over'
     ]);
   });
 
@@ -78,16 +82,21 @@ void main() {
       home: Material(
         child: Column(
           children: <Widget>[
-            PopupMenuButton<void>(
-              key: popupButtonKey,
-              itemBuilder: (BuildContext context) {
-                return <PopupMenuEntry<void>>[
-                  PopupMenuItem<void>(
-                    key: popupItemKey,
-                    child: const Text('Example'),
-                  ),
-                ];
-              },
+            Padding(
+              // The padding makes sure the menu as enough space to around to
+              // get properly aligned when displayed (`_kMenuScreenPadding`).
+              padding: const EdgeInsets.all(8.0),
+              child: PopupMenuButton<void>(
+                key: popupButtonKey,
+                itemBuilder: (BuildContext context) {
+                  return <PopupMenuEntry<void>>[
+                    PopupMenuItem<void>(
+                      key: popupItemKey,
+                      child: const Text('Example'),
+                    ),
+                  ];
+                },
+              ),
             ),
           ],
         ),
@@ -123,6 +132,11 @@ void main() {
     );
     expect(text.style.fontFamily, 'Roboto');
     expect(text.style.color, const Color(0xdd000000));
+    expect(text.style.color, const Color(0xdd000000));
+
+    final Offset topLeftButton = tester.getTopLeft(find.byType(PopupMenuButton<void>));
+    final Offset topLeftMenu = tester.getTopLeft(find.byWidget(button));
+    expect(topLeftMenu, topLeftButton);
   });
 
   testWidgets('Popup menu uses values from PopupMenuThemeData', (WidgetTester tester) async {
@@ -138,6 +152,10 @@ void main() {
         child: Column(
           children: <Widget>[
             PopupMenuButton<void>(
+              // The padding is used in the positioning of the menu when the
+              // position is `PopupMenuPosition.under`. Setting it to zero makes
+              // it easier to test.
+              padding: EdgeInsets.zero,
               key: popupButtonKey,
               itemBuilder: (BuildContext context) {
                 return <PopupMenuEntry<Object>>[
@@ -181,6 +199,10 @@ void main() {
       ).last,
     );
     expect(text.style, popupMenuTheme.textStyle);
+
+    final Offset bottomLeftButton = tester.getBottomLeft(find.byType(PopupMenuButton<void>));
+    final Offset topLeftMenu = tester.getTopLeft(find.byWidget(button));
+    expect(topLeftMenu, bottomLeftButton);
   });
 
   testWidgets('Popup menu widget properties take priority over theme', (WidgetTester tester) async {
@@ -202,20 +224,26 @@ void main() {
       home: Material(
         child: Column(
           children: <Widget>[
-            PopupMenuButton<void>(
-              key: popupButtonKey,
-              elevation: elevation,
-              color: color,
-              shape: shape,
-              itemBuilder: (BuildContext context) {
-                return <PopupMenuEntry<void>>[
-                  PopupMenuItem<void>(
-                    key: popupItemKey,
-                    textStyle: textStyle,
-                    child: const Text('Example'),
-                  ),
-                ];
-              },
+            Padding(
+              // The padding makes sure the menu as enough space to around to
+              // get properly aligned when displayed (`_kMenuScreenPadding`).
+              padding: const EdgeInsets.all(8.0),
+              child: PopupMenuButton<void>(
+                key: popupButtonKey,
+                elevation: elevation,
+                color: color,
+                shape: shape,
+                position: PopupMenuPosition.over,
+                itemBuilder: (BuildContext context) {
+                  return <PopupMenuEntry<void>>[
+                    PopupMenuItem<void>(
+                      key: popupItemKey,
+                      textStyle: textStyle,
+                      child: const Text('Example'),
+                    ),
+                  ];
+                },
+              ),
             ),
           ],
         ),
@@ -250,6 +278,10 @@ void main() {
       ).last,
     );
     expect(text.style, textStyle);
+
+    final Offset topLeftButton = tester.getTopLeft(find.byType(PopupMenuButton<void>));
+    final Offset topLeftMenu = tester.getTopLeft(find.byWidget(button));
+    expect(topLeftMenu, topLeftButton);
   });
 
   testWidgets('ThemeData.popupMenuTheme properties are utilized', (WidgetTester tester) async {