1. Stateful Hot Reload on Web is Enabled by Default

What changed:

Code / Usage Example:

# Before (older versions)
flutter run -d chrome --web-experimental-hot_reload

# In 3.35
flutter run -d chrome
# Now you get stateful hot reload by default for web

// A simple counter example to test
import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) => MaterialApp(home: CounterScreen());
}

class CounterScreen extends StatefulWidget {
  @override
  _CounterScreenState createState() => _CounterScreenState();
}

class _CounterScreenState extends State<CounterScreen> {
  int count = 0;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text("Web Hot Reload Demo")),
      body: Center(child: Text('Count: $count', style: TextStyle(fontSize: 30))),
      floatingActionButton: FloatingActionButton(
        child: Icon(Icons.add),
        onPressed: () => setState(() => count++),
      ),
    );
  }
}

flutter build web --wasm-dry-run

You might see warnings like:

WARNING: Some APIs used may not be supported in WASM target:
- dart:io
- certain plugins

Then you can revise code (replace unsupported APIs, use conditional imports, etc.).

3. Widget Previews (Experimental)

What changed:

Usage Example:

import 'package:flutter/material.dart';
// Assuming a preview widget is available
import 'package:flutter_widget_previewer/flutter_widget_previewer.dart';

@Preview(
  name: 'ProfileCard Light Mode',
  brightness: Brightness.light,
  theme: ThemeData.light(),
  locale: Locale('en'),
)
Widget buildProfileCardLight() => ProfileCard(userName: 'Alice');

@Preview(
  name: 'ProfileCard Dark Mode',
  brightness: Brightness.dark,
  theme: ThemeData.dark(),
  locale: Locale('en'),
)
Widget buildProfileCardDark() => ProfileCard(userName: 'Alice');

This allows design/QA teams to inspect layouts rapidly. Helps catch UI issues early.

4. Accessibility Improvements & Semantics Enhancements

What changed:

Code Example:

import 'package:flutter/material.dart';

class AccessibleList extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return CustomScrollView(
      slivers: [
        SliverEnsureSemantics(
          sliver: SliverList(
            delegate: SliverChildBuilderDelegate(
              (ctx, idx) => Semantics(
                label: 'Item number ${idx + 1}',
                child: ListTile(title: Text('Item ${idx + 1}')),
              ),
              childCount: 20,
            ),
          ),
        ),
      ],
    );
  }
}

Or using SemanticsLabelBuilder:

SemanticsLabelBuilder(
  label: (context, value) => 'Selected ${value.title}, $value.status',
  child: SomeWidget(),
);

5. Material & Cupertino Widget Polishing / Additions

What changed:

Code Example:

// NavigationDrawer with header and footer
NavigationDrawer(
  header: DrawerHeader(child: Text('Welcome')),
  footer: Container(
    padding: EdgeInsets.all(16),
    child: Text('Version 1.0.0'),
  ),
  children: [
    NavigationDrawerDestination(
      icon: Icon(Icons.home),
      label: Text('Home'),
    ),
    NavigationDrawerDestination(
      icon: Icon(Icons.settings),
      label: Text('Settings'),
    ),
  ],
);

6. Breaking Change: Form Widget & Slivers

What changed:

• In previous versions, you might have placed Form directly inside a list of slivers (in CustomScrollView). In 3.35, this is no longer allowed. You must wrap Form in a SliverToBoxAdapter.

Example of migration:

Before:

CustomScrollView(
  slivers: [
    Form(
      child: SliverList(
        delegate: SliverChildBuilderDelegate(
          (ctx, idx) => Text('Form item $idx'),
          childCount: 5,
        ),
      ),
    ),
  ],
);

After:

CustomScrollView(
  slivers: [
    SliverToBoxAdapter(
      child: Form(
        child: Column(
          children: List.generate(5, (idx) => Text('Form item $idx')),
        ),
      ),
    ),
    // Other slivers...
  ],
);

This change is essential to avoid runtime layout errors and to align with semantics.

7. Platform Minimum Version Bumps & Compatibility Changes

What changed:

Why this matters:

Migration Tip:

8. SensitiveContent Widget / Privacy & Security Features

What changed:

• New SensitiveContent widget (Android API 35+) allows portions of the UI to block screenshots or screen recordings, useful for sensitive data screens (financial, healthcare, etc.)

Usage Example:

import 'package:flutter/widgets.dart';
import 'package:flutter/services.dart';

class SecureScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return SensitiveContent(
      child: Scaffold(
        appBar: AppBar(title: Text('Secure Info')),
        body: Center(child: Text('Data you can’t screen-capture!')),
      ),
    );
  }
}

This prevents recording or screenshotting when the widget is in view (depending on platform support).

9. Frame / Impeller & Rendering Fixes

What changed:

Why this matters:

10. Developer Tooling & “Create with AI” / MCP Server Support

What changed:

Example use (pseudo-code / config):

# To enable widget previews (if not enabled by default):
flutter config --enable-widget-previews

# To run build with wasm dry run:
flutter build web --wasm-dry-run

Migration Tips & Checklist

Before & After Upgrade Flow