From 874804e511109a4028fd9b874836e5f82fe44103 Mon Sep 17 00:00:00 2001
From: Faisal Ansari <faisal.hiyaz@gmail.com>
Date: Fri, 8 Mar 2024 02:16:03 +0530
Subject: [PATCH] =?UTF-8?q?Fixed=20->=20DropdownMenu=20throws=20exception?=
 =?UTF-8?q?=20when=20it=20is=20in=20any=20scrollable=20l=E2=80=A6=20(#1405?=
 =?UTF-8?q?66)?=
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Fixed -> DropdownMenu throws exception when it is in any scrollable list view and scrolls quickly #139871
---
 .../lib/src/material/dropdown_menu.dart       |  3 ++
 .../test/material/dropdown_menu_test.dart     | 28 +++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/packages/flutter/lib/src/material/dropdown_menu.dart b/packages/flutter/lib/src/material/dropdown_menu.dart
index 0ec91f143ab..58d34be5dd8 100644
--- a/packages/flutter/lib/src/material/dropdown_menu.dart
+++ b/packages/flutter/lib/src/material/dropdown_menu.dart
@@ -493,6 +493,9 @@ class _DropdownMenuState<T> extends State<DropdownMenu<T>> {
 
   void refreshLeadingPadding() {
     WidgetsBinding.instance.addPostFrameCallback((_) {
+      if (!mounted) {
+        return;
+      }
       setState(() {
         leadingPadding = getWidth(_leadingKey);
       });
diff --git a/packages/flutter/test/material/dropdown_menu_test.dart b/packages/flutter/test/material/dropdown_menu_test.dart
index f3ba1aeff20..097e4ddd206 100644
--- a/packages/flutter/test/material/dropdown_menu_test.dart
+++ b/packages/flutter/test/material/dropdown_menu_test.dart
@@ -1910,6 +1910,34 @@ void main() {
     expect(tester.takeException(), isNull);
   });
 
+  // Regression test for https://github.com/flutter/flutter/issues/139871.
+  testWidgets('setState is not called through addPostFrameCallback after DropdownMenu is unmounted', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Scaffold(
+          body: ListView.builder(
+            itemCount: 500,
+            itemBuilder: (BuildContext context, int index) {
+              if (index == 250) {
+                return DropdownMenu<TestMenu>(
+                  dropdownMenuEntries: menuChildren,
+                );
+              } else {
+                return Container(height: 50);
+              }
+            },
+          ),
+        ),
+      ),
+    );
+
+    await tester.fling(find.byType(ListView), const Offset(0, -20000), 200000.0);
+
+    await tester.pumpAndSettle();
+
+    expect(tester.takeException(), isNull);
+  });
+
   testWidgets('Menu shows scrollbar when height is limited', (WidgetTester tester) async {
     final List<DropdownMenuEntry<TestMenu>> menuItems = <DropdownMenuEntry<TestMenu>>[
       DropdownMenuEntry<TestMenu>(