fix: 根本性修复导航架构，统一由main_screen管理

lib/screens/activity_list_screen.dart

@@ -1,10 +1,6 @@
 import 'package:flutter/material.dart';
 import 'package:flutter_staggered_grid_view/flutter_staggered_grid_view.dart';
-import 'publish_screen.dart';
 import 'activity_detail_screen.dart';
-import 'friends_screen.dart';
-import 'messages_screen.dart';
-import 'profile_screen.dart';
 
 class ActivityListScreen extends StatefulWidget {
   @override
@@ -12,9 +8,6 @@ class ActivityListScreen extends StatefulWidget {
 }
 
 class _ActivityListScreenState extends State<ActivityListScreen> {
-  int _selectedIndex = 0;
-  bool _showFriendsOverlay = false;
-  final _feedKey = GlobalKey<RefreshIndicatorState>();
   String? _selectedTime;
 
   // 模拟活动数据
@@ -83,98 +76,31 @@ class _ActivityListScreenState extends State<ActivityListScreen> {
     await Future.delayed(const Duration(milliseconds: 200));
   }
 
-  void _onItemTapped(int index) {
-    if (index == 2) {
-      // 中间按钮 - 跳转到发布页面
-      Navigator.push(
-        context,
-        MaterialPageRoute(builder: (context) => PublishScreen()),
-      );
-      return;
-    }
-
-    if (index == 1) {
-      setState(() {
-        _showFriendsOverlay = !_showFriendsOverlay;
-        if (_showFriendsOverlay) {
-          _selectedIndex = 0;
-        }
-      });
-      return;
-    }
-
-    if (index == 0 && _selectedIndex == 0 && !_showFriendsOverlay) {
-      _feedKey.currentState?.show();
-      return;
-    }
-
-    if (_selectedIndex != index || _showFriendsOverlay) {
-      setState(() {
-        _selectedIndex = index;
-        _showFriendsOverlay = false;
-      });
-    }
-  }
-
   @override
   Widget build(BuildContext context) {
-    // When showing messages or profile, use their own Scaffold directly
-    if (_selectedIndex == 3 || _selectedIndex == 4) {
-      return Scaffold(
-        backgroundColor: const Color(0xFFFFF8F0),
-        body: _buildBodyWithFriendsOverlay(),
-        bottomNavigationBar: _buildBottomNavigationBar(),
-      );
-    }
     return Scaffold(
       backgroundColor: const Color(0xFFFFF8F0),
-      appBar: _showFriendsOverlay
-          ? null
-          : AppBar(
-              title: Text('伴享', style: TextStyle(fontWeight: FontWeight.bold)),
-              centerTitle: true,
-              actions: [
-                IconButton(
-                  icon: Icon(Icons.search),
-                  onPressed: () {},
-                ),
-                IconButton(
-                  icon: Icon(Icons.notifications_none),
-                  onPressed: () {},
-                ),
-              ],
-            ),
-      body: _buildBodyWithFriendsOverlay(),
-      bottomNavigationBar: _buildBottomNavigationBar(),
-      floatingActionButton: _buildFloatingActionButton(),
-      floatingActionButtonLocation: FloatingActionButtonLocation.centerDocked,
-    );
-  }
-
-  Widget _buildBody() {
-    switch (_selectedIndex) {
-      case 3:
-        return const MessagesScreen();
-      case 4:
-        return const ProfileScreen();
-      default:
-        return _buildFeed();
-    }
-  }
-
-  Widget _buildBodyWithFriendsOverlay() {
-    return Stack(
-      children: [
-        _buildBody(),
-        if (_showFriendsOverlay) const Positioned.fill(child: FriendsScreen()),
-      ],
+      appBar: AppBar(
+        title: Text('伴享', style: TextStyle(fontWeight: FontWeight.bold)),
+        centerTitle: true,
+        actions: [
+          IconButton(
+            icon: Icon(Icons.search),
+            onPressed: () {},
+          ),
+          IconButton(
+            icon: Icon(Icons.notifications_none),
+            onPressed: () {},
+          ),
+        ],
+      ),
+      body: _buildFeed(),
     );
   }
 
   Widget _buildFeed() {
     final filteredActivities = _getFilteredActivities();
     return RefreshIndicator(
-      key: _feedKey,
       onRefresh: _refreshActivities,
       child: ListView(
         physics: const AlwaysScrollableScrollPhysics(),
@@ -393,91 +319,4 @@ class _ActivityListScreenState extends State<ActivityListScreen> {
     );
   }
 
-  Widget _buildBottomNavigationBar() {
-    return Container(
-      decoration: BoxDecoration(
-        color: Colors.white,
-        boxShadow: [
-          BoxShadow(
-            color: Colors.black.withOpacity(0.05),
-            blurRadius: 10,
-            offset: Offset(0, -2),
-          ),
-        ],
-      ),
-      child: SafeArea(
-        child: Container(
-          height: 60,
-          child: Row(
-            children: [
-              _buildNavItem(0, Icons.home, '首页'),
-              _buildNavItem(1, Icons.people, '好友'),
-              SizedBox(width: 60), // 中间按钮占位
-              _buildNavItem(3, Icons.message, '消息'),
-              _buildNavItem(4, Icons.person, '我的'),
-            ],
-          ),
-        ),
-      ),
-    );
-  }
-
-  Widget _buildNavItem(int index, IconData icon, String label) {
-    final isSelected = index == 1 ? _showFriendsOverlay : _selectedIndex == index;
-    return Expanded(
-      child: GestureDetector(
-        onTap: () => _onItemTapped(index),
-        behavior: HitTestBehavior.opaque,
-        child: Column(
-          mainAxisAlignment: MainAxisAlignment.center,
-          children: [
-            Icon(
-              icon,
-              color: isSelected ? Color(0xFFFF6B35) : Color(0xFF999999),
-              size: 24,
-            ),
-            SizedBox(height: 4),
-            Text(
-              label,
-              style: TextStyle(
-                fontSize: 11,
-                color: isSelected ? Color(0xFFFF6B35) : Color(0xFF999999),
-              ),
-            ),
-          ],
-        ),
-      ),
-    );
-  }
-
-  Widget _buildFloatingActionButton() {
-    return Container(
-      width: 56,
-      height: 56,
-      margin: EdgeInsets.only(top: 30),
-      decoration: BoxDecoration(
-        shape: BoxShape.circle,
-        gradient: LinearGradient(
-          colors: [Color(0xFFFF6B35), Color(0xFFFFB84D)],
-          begin: Alignment.topLeft,
-          end: Alignment.bottomRight,
-        ),
-        boxShadow: [
-          BoxShadow(
-            color: Color(0xFFFF6B35).withOpacity(0.4),
-            blurRadius: 12,
-            offset: Offset(0, 4),
-          ),
-        ],
-      ),
-      child: Material(
-        color: Colors.transparent,
-        child: InkWell(
-          onTap: () => _onItemTapped(2),
-          customBorder: CircleBorder(),
-          child: Icon(Icons.add, color: Colors.white, size: 28),
-        ),
-      ),
-    );
-  }
 }

lib/screens/main_screen.dart

@@ -1,5 +1,6 @@
 import 'package:flutter/material.dart';
-import 'home_screen.dart';
+import 'activity_list_screen.dart';
+import 'friends_screen.dart';
 import 'services_screen.dart';
 import 'ai_chat_screen.dart';
 import 'messages_screen.dart';
@@ -14,9 +15,10 @@ class MainScreen extends StatefulWidget {
 
 class _MainScreenState extends State<MainScreen> {
   int _currentIndex = 0;
-  
+
   final _screens = [
-    HomeScreen(),
+    ActivityListScreen(),
+    FriendsScreen(),
     ServicesScreen(),
     AiChatScreen(),
     MessagesScreen(),
@@ -28,12 +30,13 @@ class _MainScreenState extends State<MainScreen> {
     return Scaffold(
       body: IndexedStack(index: _currentIndex, children: _screens),
       floatingActionButton: _buildGlobalFab(),
-      floatingActionButtonLocation: FloatingActionButtonLocation.endFloat,
+      floatingActionButtonLocation: FloatingActionButtonLocation.centerDocked,
       bottomNavigationBar: BottomNavigationBar(
         currentIndex: _currentIndex,
         onTap: (i) => setState(() => _currentIndex = i),
         items: const [
           BottomNavigationBarItem(icon: Icon(Icons.home_outlined), activeIcon: Icon(Icons.home), label: '首页'),
+          BottomNavigationBarItem(icon: Icon(Icons.people_outline), activeIcon: Icon(Icons.people), label: '好友'),
           BottomNavigationBarItem(icon: Icon(Icons.grid_view_outlined), activeIcon: Icon(Icons.grid_view), label: '服务'),
           BottomNavigationBarItem(icon: Icon(Icons.smart_toy_outlined), activeIcon: Icon(Icons.smart_toy), label: 'AI管家'),
           BottomNavigationBarItem(icon: Icon(Icons.message_outlined), activeIcon: Icon(Icons.message), label: '消息'),
@@ -43,22 +46,39 @@ class _MainScreenState extends State<MainScreen> {
     );
   }
 
-  Widget? _buildGlobalFab() {
-    if (_currentIndex == 0) {
-      return null;
-    }
-
-    return FloatingActionButton.extended(
-      onPressed: () {
-        Navigator.push(
-          context,
-          MaterialPageRoute(builder: (_) => CreateActivityScreen()),
-        );
-      },
-      icon: const Icon(Icons.add),
-      label: const Text('发起活动', style: TextStyle(fontSize: 16)),
-      backgroundColor: const Color(0xFF1976D2),
-      foregroundColor: Colors.white,
+  Widget _buildGlobalFab() {
+    return Container(
+      width: 56,
+      height: 56,
+      margin: const EdgeInsets.only(top: 30),
+      decoration: BoxDecoration(
+        shape: BoxShape.circle,
+        gradient: const LinearGradient(
+          colors: [Color(0xFFFF6B35), Color(0xFFFFB84D)],
+          begin: Alignment.topLeft,
+          end: Alignment.bottomRight,
+        ),
+        boxShadow: [
+          BoxShadow(
+            color: const Color(0xFFFF6B35).withOpacity(0.35),
+            blurRadius: 12,
+            offset: const Offset(0, 4),
+          ),
+        ],
+      ),
+      child: Material(
+        color: Colors.transparent,
+        child: InkWell(
+          onTap: () {
+            Navigator.push(
+              context,
+              MaterialPageRoute(builder: (_) => CreateActivityScreen()),
+            );
+          },
+          customBorder: const CircleBorder(),
+          child: const Icon(Icons.add, color: Colors.white, size: 28),
+        ),
+      ),
     );
   }
 }