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Real-timeCollaboration

Build powerful collaborative applications with InstantDB’s real-time synchronization, presence system, and conflict resolution. Create experiences like shared whiteboards, collaborative editors, multiplayer games, and team workspaces.

Complete Collaborative Editor

Here’s a full example of a collaborative text editor with cursors, typing indicators, and presence:

class CollaborativeEditor extends StatefulWidget {
  @override
  State<CollaborativeEditor> createState() => _CollaborativeEditorState();
}
 
class _CollaborativeEditorState extends State<CollaborativeEditor> {
  final TextEditingController _controller = TextEditingController();
  final FocusNode _focusNode = FocusNode();
  InstantRoom? _room;
  String? _documentId;
  Timer? _typingTimer;
  
  @override
  void initState() {
    super.initState();
    _documentId = 'doc-${widget.documentId}';
    _initializeCollaboration();
  }
  
  void _initializeCollaboration() {
    final db = InstantProvider.of(context);
    final currentUser = db.auth.currentUser.value;
    
    // Join collaboration room
    _room = db.presence.joinRoom(_documentId!, initialPresence: {
      'userName': currentUser?.email ?? 'Anonymous',
      'status': 'editing',
      'color': _generateUserColor(currentUser?.id ?? 'anonymous'),
    });
    
    // Listen to document changes
    _subscribeToDocument();
    
    // Handle text selection changes for cursor position
    _controller.addListener(_updateCursorPosition);
  }
  
  void _subscribeToDocument() {
    final db = InstantProvider.of(context);
    
    // Subscribe to document content changes
    db.subscribeQuery({
      'documents': {
        'where': {'id': _documentId},
      }
    }).stream.listen((result) {
      final documents = result.data?['documents'] as List? ?? [];
      if (documents.isNotEmpty) {
        final document = documents.first as Map<String, dynamic>;
        final content = document['content'] as String? ?? '';
        
        // Update content if different (avoid cursor jumps)
        if (_controller.text != content) {
          final selection = _controller.selection;
          _controller.text = content;
          _controller.selection = selection;
        }
      }
    });
  }
  
  void _updateCursorPosition() {
    final selection = _controller.selection;
    if (selection.isValid && _room != null) {
      _room!.updateCursor(
        x: selection.baseOffset.toDouble(),
        y: 0, // For text, we use line-based positioning
      );
    }
  }
  
  void _handleTextChange(String text) {
    // Update document with debouncing
    _typingTimer?.cancel();
    _room?.setTyping(true);
    
    _typingTimer = Timer(const Duration(milliseconds: 500), () async {
      await _saveDocument(text);
      _room?.setTyping(false);
    });
  }
  
  Future<void> _saveDocument(String content) async {
    final db = InstantProvider.of(context);
    
    await db.transact([
      db.update(_documentId!, {
        'content': content,
        'lastModified': DateTime.now().millisecondsSinceEpoch,
      }),
    ]);
  }
  
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Collaborative Editor'),
        actions: [
          // Show connected users
          UserAvatars(room: _room!),
          const SizedBox(width: 16),
        ],
      ),
      body: Column(
        children: [
          // Connection status
          ConnectionStatusBanner(),
          
          // Typing indicators
          TypingIndicatorBanner(room: _room!),
          
          // Editor with cursor overlay
          Expanded(
            child: Stack(
              children: [
                // Main text editor
                Padding(
                  padding: const EdgeInsets.all(16),
                  child: TextField(
                    controller: _controller,
                    focusNode: _focusNode,
                    maxLines: null,
                    expands: true,
                    onChanged: _handleTextChange,
                    decoration: const InputDecoration(
                      border: InputBorder.none,
                      hintText: 'Start typing...',
                    ),
                  ),
                ),
                
                // Collaborative cursors overlay
                CursorOverlay(room: _room!),
              ],
            ),
          ),
        ],
      ),
    );
  }
}

Real-time Whiteboard

Create a collaborative drawing canvas:

class CollaborativeWhiteboard extends StatefulWidget {
  @override
  State<CollaborativeWhiteboard> createState() => _CollaborativeWhiteboardState();
}
 
class _CollaborativeWhiteboardState extends State<CollaborativeWhiteboard> {
  InstantRoom? _room;
  final List<DrawingPoint> _points = [];
  String? _currentStroke;
  
  @override
  void initState() {
    super.initState();
    _initializeWhiteboard();
  }
  
  void _initializeWhiteboard() {
    final db = InstantProvider.of(context);
    
    _room = db.presence.joinRoom('whiteboard', initialPresence: {
      'userName': 'Artist ${DateTime.now().millisecondsSinceEpoch % 1000}',
      'tool': 'pen',
      'color': '#000000',
    });
    
    // Subscribe to drawing strokes
    db.subscribeQuery({
      'strokes': {
        'where': {'whiteboardId': 'main'},
        'orderBy': {'createdAt': 'asc'},
      }
    }).stream.listen((result) {
      final strokes = result.data?['strokes'] as List? ?? [];
      setState(() {
        _points.clear();
        _points.addAll(strokes.map((s) => DrawingPoint.fromJson(s)));
      });
    });
  }
  
  void _handlePanStart(DragStartDetails details) {
    _currentStroke = db.id();
    _room?.setPresence({'status': 'drawing'});
    
    final point = DrawingPoint(
      id: _currentStroke!,
      x: details.localPosition.dx,
      y: details.localPosition.dy,
      isStart: true,
    );
    
    _addPoint(point);
  }
  
  void _handlePanUpdate(DragUpdateDetails details) {
    if (_currentStroke == null) return;
    
    final point = DrawingPoint(
      id: _currentStroke!,
      x: details.localPosition.dx,
      y: details.localPosition.dy,
      isStart: false,
    );
    
    _addPoint(point);
    
    // Update cursor position for others
    _room?.updateCursor(
      x: details.localPosition.dx,
      y: details.localPosition.dy,
    );
  }
  
  void _handlePanEnd(DragEndDetails details) {
    _currentStroke = null;
    _room?.setPresence({'status': 'idle'});
  }
  
  Future<void> _addPoint(DrawingPoint point) async {
    final db = InstantProvider.of(context);
    
    await db.transact([
      ...db.create('points', {
        'id': db.id(),
        'strokeId': point.id,
        'x': point.x,
        'y': point.y,
        'isStart': point.isStart,
        'whiteboardId': 'main',
        'createdAt': DateTime.now().millisecondsSinceEpoch,
      }),
    ]);
  }
  
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Collaborative Whiteboard'),
        actions: [
          UserAvatars(room: _room!),
        ],
      ),
      body: Stack(
        children: [
          // Drawing canvas
          GestureDetector(
            onPanStart: _handlePanStart,
            onPanUpdate: _handlePanUpdate,
            onPanEnd: _handlePanEnd,
            child: CustomPaint(
              painter: WhiteboardPainter(_points),
              size: Size.infinite,
            ),
          ),
          
          // Collaborative cursors
          CursorOverlay(room: _room!),
          
          // Reactions overlay
          ReactionsOverlay(room: _room!),
        ],
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _clearCanvas,
        child: const Icon(Icons.clear),
      ),
    );
  }
}

Team Chat with Presence

Build a team chat with rich presence information:

class TeamChat extends StatefulWidget {
  final String teamId;
  
  const TeamChat({super.key, required this.teamId});
  
  @override
  State<TeamChat> createState() => _TeamChatState();
}
 
class _TeamChatState extends State<TeamChat> {
  final TextEditingController _messageController = TextEditingController();
  InstantRoom? _room;
  StreamSubscription? _chatSubscription;
  final List<ChatMessage> _messages = [];
  
  @override
  void initState() {
    super.initState();
    _initializeChat();
  }
  
  void _initializeChat() {
    final db = InstantProvider.of(context);
    final currentUser = db.auth.currentUser.value;
    
    // Join team room
    _room = db.presence.joinRoom('team-${widget.teamId}', initialPresence: {
      'userName': currentUser?.email ?? 'Anonymous',
      'status': 'online',
      'avatar': currentUser?.metadata?['avatar'],
      'lastSeen': DateTime.now().millisecondsSinceEpoch,
    });
    
    // Subscribe to chat messages
    _chatSubscription = _room!.subscribeTopic('messages').listen((data) {
      final message = ChatMessage.fromJson(data);
      setState(() {
        _messages.add(message);
        _messages.sort((a, b) => a.timestamp.compareTo(b.timestamp));
      });
    });
    
    // Load existing messages
    _loadChatHistory();
    
    // Update typing status
    _messageController.addListener(_handleTyping);
  }
  
  Timer? _typingTimer;
  void _handleTyping() {
    _room?.setTyping(true);
    
    _typingTimer?.cancel();
    _typingTimer = Timer(const Duration(seconds: 2), () {
      _room?.setTyping(false);
    });
  }
  
  Future<void> _loadChatHistory() async {
    final db = InstantProvider.of(context);
    
    final result = await db.queryOnce({
      'messages': {
        'where': {'teamId': widget.teamId},
        'orderBy': {'timestamp': 'asc'},
        'limit': 100,
      }
    });
    
    final messages = result.data?['messages'] as List? ?? [];
    setState(() {
      _messages.clear();
      _messages.addAll(messages.map((m) => ChatMessage.fromJson(m)));
    });
  }
  
  Future<void> _sendMessage() async {
    final text = _messageController.text.trim();
    if (text.isEmpty) return;
    
    final db = InstantProvider.of(context);
    final currentUser = db.auth.currentUser.value;
    
    final message = {
      'id': db.id(),
      'teamId': widget.teamId,
      'userId': currentUser?.id ?? 'anonymous',
      'userName': currentUser?.email ?? 'Anonymous',
      'text': text,
      'timestamp': DateTime.now().millisecondsSinceEpoch,
    };
    
    // Save to database
    await db.transact([
      ...db.create('messages', message),
    ]);
    
    // Broadcast via presence
    await _room!.publishTopic('messages', message);
    
    _messageController.clear();
    _room?.setTyping(false);
  }
  
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Team ${widget.teamId}'),
        actions: [
          // Team presence indicators
          Watch((context) {
            final presence = _room?.getPresence().value ?? {};
            final onlineCount = presence.values
                .where((p) => p.data['status'] == 'online')
                .length;
            
            return Padding(
              padding: const EdgeInsets.all(8.0),
              child: Chip(
                label: Text('$onlineCount online'),
                avatar: const Icon(Icons.people, size: 16),
              ),
            );
          }),
        ],
      ),
      body: Column(
        children: [
          // Messages list
          Expanded(
            child: ListView.builder(
              itemCount: _messages.length,
              itemBuilder: (context, index) {
                final message = _messages[index];
                return MessageBubble(
                  message: message,
                  isOwn: message.userId == 
                         InstantProvider.of(context).auth.currentUser.value?.id,
                );
              },
            ),
          ),
          
          // Typing indicators
          TypingIndicator(room: _room!),
          
          // Message input
          Container(
            padding: const EdgeInsets.all(8),
            child: Row(
              children: [
                Expanded(
                  child: TextField(
                    controller: _messageController,
                    decoration: const InputDecoration(
                      hintText: 'Type a message...',
                      border: OutlineInputBorder(),
                    ),
                    onSubmitted: (_) => _sendMessage(),
                  ),
                ),
                const SizedBox(width: 8),
                IconButton(
                  onPressed: _sendMessage,
                  icon: const Icon(Icons.send),
                ),
              ],
            ),
          ),
        ],
      ),
    );
  }
}

Collaborative Task Management

Build a shared task board with real-time updates:

class CollaborativeTaskBoard extends StatefulWidget {
  @override
  State<CollaborativeTaskBoard> createState() => _CollaborativeTaskBoardState();
}
 
class _CollaborativeTaskBoardState extends State<CollaborativeTaskBoard> {
  InstantRoom? _room;
  
  @override
  void initState() {
    super.initState();
    _initializeTaskBoard();
  }
  
  void _initializeTaskBoard() {
    final db = InstantProvider.of(context);
    final currentUser = db.auth.currentUser.value;
    
    _room = db.presence.joinRoom('task-board', initialPresence: {
      'userName': currentUser?.email ?? 'Team Member',
      'status': 'viewing',
      'currentColumn': null,
    });
  }
  
  Future<void> _moveTask(String taskId, String toColumn) async {
    final db = InstantProvider.of(context);
    
    // Optimistic update with presence
    _room?.setPresence({
      'status': 'moving_task',
      'taskId': taskId,
      'toColumn': toColumn,
    });
    
    // Send reaction for visual feedback
    await _room?.sendReaction('📋', metadata: {
      'action': 'task_moved',
      'taskId': taskId,
      'column': toColumn,
    });
    
    await db.transact([
      db.update(taskId, {
        'status': toColumn,
        'updatedAt': DateTime.now().millisecondsSinceEpoch,
      }),
    ]);
    
    _room?.setPresence({'status': 'viewing'});
  }
  
  @override
  Widget build(BuildContext context) {
    final db = InstantProvider.of(context);
    
    return Scaffold(
      appBar: AppBar(
        title: const Text('Task Board'),
        actions: [
          UserAvatars(room: _room!),
          IconButton(
            onPressed: _addNewTask,
            icon: const Icon(Icons.add),
          ),
        ],
      ),
      body: Row(
        children: [
          // Task columns
          Expanded(
            child: InstantBuilder(
              query: {
                'tasks': {
                  'where': {'boardId': 'main'},
                  'orderBy': {'createdAt': 'desc'},
                }
              },
              builder: (context, result) {
                final tasks = result.data?['tasks'] as List? ?? [];
                
                return Row(
                  children: [
                    TaskColumn(
                      title: 'To Do',
                      status: 'todo',
                      tasks: tasks.where((t) => t['status'] == 'todo').toList(),
                      onTaskMoved: _moveTask,
                      room: _room!,
                    ),
                    TaskColumn(
                      title: 'In Progress',
                      status: 'inprogress',
                      tasks: tasks.where((t) => t['status'] == 'inprogress').toList(),
                      onTaskMoved: _moveTask,
                      room: _room!,
                    ),
                    TaskColumn(
                      title: 'Done',
                      status: 'done',
                      tasks: tasks.where((t) => t['status'] == 'done').toList(),
                      onTaskMoved: _moveTask,
                      room: _room!,
                    ),
                  ],
                );
              },
            ),
          ),
        ],
      ),
    );
  }
}

Conflict Resolution

InstantDB automatically handles conflicts, but you can implement custom resolution:

class ConflictAwareDocument extends StatefulWidget {
  @override
  State<ConflictAwareDocument> createState() => _ConflictAwareDocumentState();
}
 
class _ConflictAwareDocumentState extends State<ConflictAwareDocument> {
  final TextEditingController _controller = TextEditingController();
  String? _localVersion;
  String? _serverVersion;
  
  void _handleConflict(String localContent, String serverContent) {
    if (localContent == serverContent) return;
    
    // Show conflict resolution UI
    showDialog(
      context: context,
      builder: (context) => ConflictResolutionDialog(
        localVersion: localContent,
        serverVersion: serverContent,
        onResolved: _resolveConflict,
      ),
    );
  }
  
  Future<void> _resolveConflict(String resolvedContent) async {
    final db = InstantProvider.of(context);
    
    await db.transact([
      db.update('document-id', {
        'content': resolvedContent,
        'lastModified': DateTime.now().millisecondsSinceEpoch,
        'resolvedBy': db.auth.currentUser.value?.id,
      }),
    ]);
    
    _controller.text = resolvedContent;
  }
  
  @override
  Widget build(BuildContext context) {
    return InstantBuilder(
      query: {'documents': {'where': {'id': 'document-id'}}},
      builder: (context, result) {
        final documents = result.data?['documents'] as List? ?? [];
        if (documents.isNotEmpty) {
          final document = documents.first as Map<String, dynamic>;
          final serverContent = document['content'] as String? ?? '';
          
          // Check for conflicts
          if (_localVersion != null && 
              _localVersion != serverContent && 
              _controller.text != serverContent) {
            WidgetsBinding.instance.addPostFrameCallback((_) {
              _handleConflict(_controller.text, serverContent);
            });
          }
        }
        
        return TextField(
          controller: _controller,
          onChanged: (text) => _localVersion = text,
        );
      },
    );
  }
}

Performance Optimization

Optimize collaborative features for large teams:

class OptimizedCollaboration {
  static const int MAX_CURSORS = 10;
  static const Duration PRESENCE_THROTTLE = Duration(milliseconds: 100);
  static const Duration TYPING_DEBOUNCE = Duration(milliseconds: 300);
  
  // Throttle cursor updates
  static Timer? _cursorTimer;
  static void updateCursor(InstantRoom room, double x, double y) {
    _cursorTimer?.cancel();
    _cursorTimer = Timer(PRESENCE_THROTTLE, () {
      room.updateCursor(x: x, y: y);
    });
  }
  
  // Limit displayed cursors
  static List<MapEntry<String, dynamic>> getLimitedCursors(
    Map<String, dynamic> allCursors,
  ) {
    final entries = allCursors.entries.toList();
    entries.sort((a, b) {
      final aTime = a.value.data['lastUpdate'] ?? 0;
      final bTime = b.value.data['lastUpdate'] ?? 0;
      return bTime.compareTo(aTime);
    });
    
    return entries.take(MAX_CURSORS).toList();
  }
  
  // Batch presence updates
  static void batchPresenceUpdate(
    InstantRoom room,
    Map<String, dynamic> updates,
  ) {
    Timer(PRESENCE_THROTTLE, () {
      room.setPresence(updates);
    });
  }
}

Best Practices

1. Handle Connection States

Always show connection status in collaborative apps:

Widget buildConnectionAwareUI() {
  return Column(
    children: [
      ConnectionStatusBanner(),
      // Your collaborative UI
    ],
  );
}

2. Provide Visual Feedback

Show user actions with reactions and animations:

void _showCollaborativeAction(String action, String user) {
  _room?.sendReaction('✨', metadata: {
    'action': action,
    'user': user,
    'timestamp': DateTime.now().millisecondsSinceEpoch,
  });
}

3. Handle Graceful Degradation

Ensure your app works offline:

Widget buildOfflineCapableFeature() {
  return Watch((context) {
    final isOnline = db.syncEngine?.connectionStatus.value ?? false;
    
    return Column(
      children: [
        if (!isOnline) OfflineIndicator(),
        // Feature works regardless of connection
        YourFeature(),
      ],
    );
  });
}

4. Clean Up Resources

Always clean up presence and subscriptions:

@override
void dispose() {
  _room?.setPresence({'status': 'offline'});
  _chatSubscription?.cancel();
  _typingTimer?.cancel();
  super.dispose();
}

Next Steps

Explore more collaborative patterns:

Presence