[DropdownMenu] add helperText & errorText to DropdownMenu Widget (#123775)

[DropdownMenu] add helperText & errorText to DropdownMenu Widget

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

@@ -127,6 +127,8 @@ class DropdownMenu<T> extends StatefulWidget {
     this.trailingIcon,
     this.label,
     this.hintText,
+    this.helperText,
+    this.errorText,
     this.selectedTrailingIcon,
     this.enableFilter = false,
     this.enableSearch = true,
@@ -183,6 +185,31 @@ class DropdownMenu<T> extends StatefulWidget {
   /// Defaults to null;
   final String? hintText;
 
+  /// Text that provides context about the [DropdownMenu]'s value, such
+  /// as how the value will be used.
+  ///
+  /// If non-null, the text is displayed below the input field, in
+  /// the same location as [errorText]. If a non-null [errorText] value is
+  /// specified then the helper text is not shown.
+  ///
+  /// Defaults to null;
+  ///
+  /// See also:
+  ///
+  /// * [InputDecoration.helperText], which is the text that provides context about the [InputDecorator.child]'s value.
+  final String? helperText;
+
+  /// Text that appears below the input field and the border to show the error message.
+  ///
+  /// If non-null, the border's color animates to red and the [helperText] is not shown.
+  ///
+  /// Defaults to null;
+  ///
+  /// See also:
+  ///
+  /// * [InputDecoration.errorText], which is the text that appears below the [InputDecorator.child] and the border.
+  final String? errorText;
+
   /// An optional icon at the end of the text field to indicate that the text
   /// field is pressed.
   ///
@@ -579,6 +606,8 @@ class _DropdownMenuState<T> extends State<DropdownMenu<T>> {
                     enabled: widget.enabled,
                     label: widget.label,
                     hintText: widget.hintText,
+                    helperText: widget.helperText,
+                    errorText: widget.errorText,
                     prefixIcon: widget.leadingIcon != null ? Container(
                       key: _leadingKey,
                       child: widget.leadingIcon

packages/flutter/test/material/dropdown_menu_test.dart

@@ -1110,6 +1110,123 @@ void main() {
     expect(textInput1.width, 200);
     expect(menu1.width, 200);
   });
+
+  testWidgets('Semantics does not include hint when input is not empty', (WidgetTester tester) async {
+    final ThemeData themeData = ThemeData();
+    const String hintText = 'I am hintText';
+    TestMenu? selectedValue;
+    final TextEditingController controller = TextEditingController();
+
+    await tester.pumpWidget(
+      StatefulBuilder(
+        builder: (BuildContext context, StateSetter setState) => MaterialApp(
+          theme: themeData,
+          home: Scaffold(
+            body: Center(
+              child: DropdownMenu<TestMenu>(
+                requestFocusOnTap: true,
+                dropdownMenuEntries: menuChildren,
+                hintText: hintText,
+                onSelected: (TestMenu? value) {
+                  setState(() {
+                    selectedValue = value;
+                  });
+                },
+                controller: controller,
+              ),
+            ),
+          ),
+        ),
+      ),
+    );
+    final SemanticsNode node = tester.getSemantics(find.text(hintText));
+
+    expect(selectedValue?.label, null);
+    expect(node.label, hintText);
+    expect(node.value, '');
+
+    await tester.tap(find.byType(DropdownMenu<TestMenu>));
+    await tester.pumpAndSettle();
+    await tester.tap(find.widgetWithText(MenuItemButton, 'Item 3').last);
+    await tester.pumpAndSettle();
+    expect(selectedValue?.label, 'Item 3');
+    expect(node.label, '');
+    expect(node.value, 'Item 3');
+  });
+
+  testWidgets('helperText is not visible when errorText is not null', (WidgetTester tester) async {
+    final ThemeData themeData = ThemeData();
+    const String helperText = 'I am helperText';
+    const String errorText = 'I am errorText';
+
+    Widget buildFrame(bool hasError) {
+      return MaterialApp(
+        theme: themeData,
+        home: Scaffold(
+          body: Center(
+            child: DropdownMenu<TestMenu>(
+              dropdownMenuEntries: menuChildren,
+              helperText: helperText,
+              errorText: hasError ? errorText : null,
+            ),
+          ),
+        ),
+      );
+    }
+
+    await tester.pumpWidget(buildFrame(false));
+    expect(find.text(helperText), findsOneWidget);
+    expect(find.text(errorText), findsNothing);
+
+    await tester.pumpWidget(buildFrame(true));
+    await tester.pumpAndSettle();
+    expect(find.text(helperText), findsNothing);
+    expect(find.text(errorText), findsOneWidget);
+  });
+
+  testWidgets('DropdownMenu can respect helperText when helperText is not null', (WidgetTester tester) async {
+    final ThemeData themeData = ThemeData();
+    const String helperText = 'I am helperText';
+
+    Widget buildFrame() {
+      return MaterialApp(
+        theme: themeData,
+        home: Scaffold(
+          body: Center(
+            child: DropdownMenu<TestMenu>(
+              dropdownMenuEntries: menuChildren,
+              helperText: helperText,
+            ),
+          ),
+        ),
+      );
+    }
+
+    await tester.pumpWidget(buildFrame());
+    expect(find.text(helperText), findsOneWidget);
+  });
+
+  testWidgets('DropdownMenu can respect errorText when errorText is not null', (WidgetTester tester) async {
+    final ThemeData themeData = ThemeData();
+    const String errorText = 'I am errorText';
+
+    Widget buildFrame() {
+      return MaterialApp(
+        theme: themeData,
+        home: Scaffold(
+          body: Center(
+            child: DropdownMenu<TestMenu>(
+              dropdownMenuEntries: menuChildren,
+              errorText: errorText,
+            ),
+          ),
+        ),
+      );
+    }
+
+    await tester.pumpWidget(buildFrame());
+    expect(find.text(errorText), findsOneWidget);
+  });
 }
 
 enum TestMenu {