From 4b33f98a0120aeaa00abf2f095fcd2cc080906c0 Mon Sep 17 00:00:00 2001
From: Bruno Leroux <bruno.leroux@gmail.com>
Date: Mon, 17 Nov 2025 23:14:49 +0100
Subject: [PATCH] Add DropdownMenuFormField.decorationBuilder (#178640)

## Description

This PR adds `DropdownMenuFormField.decorationBuilder` and passes it to
the underlying `DropdownMenu`.

## Related Issue

Follow-up to https://github.com/flutter/flutter/pull/176264 which added
`DropdownMenu.decorationBuilder`.

## Tests

- Adds 1 test.
---
 .../material/dropdown_menu_form_field.dart    |  2 ++
 .../dropdown_menu_form_field_test.dart        | 30 +++++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/packages/flutter/lib/src/material/dropdown_menu_form_field.dart b/packages/flutter/lib/src/material/dropdown_menu_form_field.dart
index 405e0f89c16..40c23fc2d08 100644
--- a/packages/flutter/lib/src/material/dropdown_menu_form_field.dart
+++ b/packages/flutter/lib/src/material/dropdown_menu_form_field.dart
@@ -50,6 +50,7 @@ class DropdownMenuFormField<T extends Object> extends FormField<T> {
     TextAlign textAlign = TextAlign.start,
     // TODO(bleroux): Clean this up once `InputDecorationTheme` is fully normalized.
     Object? inputDecorationTheme,
+    DropdownMenuDecorationBuilder? decorationBuilder,
     MenuStyle? menuStyle,
     this.controller,
     T? initialSelection,
@@ -95,6 +96,7 @@ class DropdownMenuFormField<T extends Object> extends FormField<T> {
                textStyle: textStyle,
                textAlign: textAlign,
                inputDecorationTheme: inputDecorationTheme,
+               decorationBuilder: decorationBuilder,
                menuStyle: menuStyle,
                controller: state.textFieldController,
                initialSelection: state.value,
diff --git a/packages/flutter/test/material/dropdown_menu_form_field_test.dart b/packages/flutter/test/material/dropdown_menu_form_field_test.dart
index 4f884b504e3..3b5ea0ed49c 100644
--- a/packages/flutter/test/material/dropdown_menu_form_field_test.dart
+++ b/packages/flutter/test/material/dropdown_menu_form_field_test.dart
@@ -472,6 +472,36 @@ void main() {
     expect(dropdownMenu.inputDecorationTheme, inputDecorationTheme);
   });
 
+  testWidgets('Passes decorationBuilder to underlying DropdownMenu', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Scaffold(body: DropdownMenuFormField<MenuItem>(dropdownMenuEntries: menuEntries)),
+      ),
+    );
+
+    // Check default value.
+    DropdownMenu<MenuItem> dropdownMenu = tester.widget(find.byType(DropdownMenu<MenuItem>));
+    expect(dropdownMenu.decorationBuilder, null);
+
+    InputDecoration buildDecoration(BuildContext context, MenuController controller) {
+      return const InputDecoration(labelText: 'labelText');
+    }
+
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Scaffold(
+          body: DropdownMenuFormField<MenuItem>(
+            decorationBuilder: buildDecoration,
+            dropdownMenuEntries: menuEntries,
+          ),
+        ),
+      ),
+    );
+
+    dropdownMenu = tester.widget(find.byType(DropdownMenu<MenuItem>));
+    expect(dropdownMenu.decorationBuilder, buildDecoration);
+  });
+
   testWidgets('Passes menuStyle to underlying DropdownMenu', (WidgetTester tester) async {
     await tester.pumpWidget(
       MaterialApp(