BLoC & Data - CometChat Docs

Each component’s BLoC manages data fetching, state transitions, and business logic. You can configure it via RequestBuilders, provide a custom BLoC instance, or extend the default one.

Configuring Data Fetching with RequestBuilders

Use request builders to control what data the component fetches. Pass the builder instance — not the result of .build().

Dart

CometChatMessageList(
  user: user,
  messagesRequestBuilder: MessagesRequestBuilder()
    ..uid = user.uid
    ..searchKeyword = 'hello'
    ..limit = 30,
)

The following parameters in MessagesRequestBuilder will always be altered inside the message list: UID, GUID, types, categories.

Request Builder by Component

Component	Builder Property	Builder Type
`CometChatConversations`	`conversationsRequestBuilder`	`ConversationsRequestBuilder`
`CometChatUsers`	`usersRequestBuilder`	`UsersRequestBuilder`
`CometChatGroups`	`groupsRequestBuilder`	`GroupsRequestBuilder`
`CometChatGroupMembers`	`groupMembersRequestBuilder`	`GroupMembersRequestBuilder`
`CometChatMessageList`	`messagesRequestBuilder`	`MessagesRequestBuilder`

Providing a Custom BLoC

Each component accepts an optional BLoC parameter. Provide your own instance to override default behavior:

Dart

final myBloc = MessageListBloc(
  user: user,
  parentMessageId: null,
  types: MessageTemplateUtils.getAllMessageTypes(),
  categories: MessageTemplateUtils.getAllMessageCategories(),
);

CometChatMessageList(
  user: user,
  messageListBloc: myBloc,
)

BLoC Parameters by Component

Component	BLoC Property	BLoC Type
`CometChatConversations`	`conversationsBloc`	`ConversationsBloc`
`CometChatMessageList`	`messageListBloc`	`MessageListBloc`
`CometChatMessageComposer`	`messageComposerBloc`	`MessageComposerBloc`

Extending the Default BLoC

Extend the default BLoC class and override hooks to add custom behavior:

Dart

class CustomMessageListBloc extends MessageListBloc {
  CustomMessageListBloc({required User user})
      : super(user: user);

  @override
  void onItemAdded(BaseMessage item, List<BaseMessage> updatedList) {
    // Custom logic when a message is added
    debugPrint('Message added: ${item.id}');
    super.onItemAdded(item, updatedList);
  }

  @override
  void onItemRemoved(BaseMessage item, List<BaseMessage> updatedList) {
    // Custom logic when a message is removed
    super.onItemRemoved(item, updatedList);
  }

  @override
  void onItemUpdated(BaseMessage oldItem, BaseMessage newItem, List<BaseMessage> updatedList) {
    // Custom logic when a message is updated
    super.onItemUpdated(oldItem, newItem, updatedList);
  }
}

ListBase Hooks

All list-based BLoCs use the ListBase mixin with these override hooks:

Hook	Called When
`onItemAdded(item, updatedList)`	An item is added to the list
`onItemRemoved(item, updatedList)`	An item is removed from the list
`onItemUpdated(oldItem, newItem, updatedList)`	An item is updated in the list
`onListCleared(previousList)`	The list is cleared
`onListReplaced(previousList, newList)`	The entire list is replaced

Component-Specific BLoC Events

Each component’s BLoC has its own events and methods. See the individual component docs for details:

Lifecycle Callbacks

Dart

CometChatMessageList(
  user: user,
  onLoad: (messages) {
    debugPrint('Loaded ${messages.length} messages');
  },
  onEmpty: () {
    debugPrint('No messages found');
  },
  onError: (e) {
    debugPrint('Error: ${e.message}');
  },
)

Message List — Full message list component reference.
Customization Overview — See all customization categories.

Repository & Datasource Overrides

Both CometChatConversations and CometChatMessageList follow the same clean architecture stack. There are two override points:

Widget → BLoC → UseCase → Repository → DataSource (Remote + Local)
                  ↑               ↑
          override here    or here

1. Datasource Override

Implement the abstract datasource interfaces to swap the data layer entirely — e.g. a REST API instead of the CometChat SDK, or a persistent cache instead of in-memory.

Conversations

Dart

abstract class ConversationsRemoteDataSource {
  Future<List<Conversation>> getConversations({int limit, String? fromId});
  Future<Conversation> getConversation(String conversationId);
  Future<void> deleteConversation(String conversationWith, String conversationType);
  Future<void> markMessageAsRead(BaseMessage message);
  Future<Conversation> updateConversation(Conversation conversation);
}

abstract class ConversationsLocalDataSource {
  Future<void> cacheConversations(List<Conversation> conversations);
  Future<List<Conversation>> getCachedConversations();
  Future<void> cacheConversation(Conversation conversation);
  Future<Conversation?> getCachedConversation(String conversationId);
  Future<void> removeCachedConversation(String conversationId);
  Future<void> clearCache();
  Future<bool> hasCachedData();
}

Message List

Dart

abstract class MessageListRemoteDataSource {
  Future<GetMessagesResult> getMessages({...});
  Future<List<BaseMessage>> fetchPreviousMessages({required MessagesRequest request});
  Future<List<BaseMessage>> fetchNextMessages({required MessagesRequest request});
  Future<void> markAsRead(BaseMessage message);
  Future<void> markAsDelivered(BaseMessage message);
  Future<User?> getLoggedInUser();
  Future<Conversation> getConversation({...});
  Future<Conversation> markMessageAsUnread(BaseMessage message);
}

abstract class MessageListLocalDataSource {
  Future<void> cacheMessages(String conversationId, List<BaseMessage> messages);
  Future<List<BaseMessage>> getCachedMessages(String conversationId);
  // ... cache CRUD methods
}

2. Repository Override

The repository interfaces sit above the datasources. Override here to change business logic — caching strategy, error handling, retry logic — without touching the datasource layer.

Conversations

Dart

abstract class ConversationsRepository {
  Future<Result<List<Conversation>>> getConversations({int limit, String? fromId});
  Future<Result<Conversation>> getConversationById(String conversationId);
  Future<Result<void>> deleteConversation(String conversationId);
  Future<Result<Conversation>> updateConversation(Conversation conversation);
  Future<Result<User?>> getLoggedInUser();
  Future<Result<void>> markAsDelivered(BaseMessage message);
  Future<Result<Conversation>> getConversation({...});
}

Message List

Dart

abstract class MessageListRepository {
  Future<Result<List<BaseMessage>>> getMessages({...});
  Future<Result<List<BaseMessage>>> fetchPreviousMessages({...});
  Future<Result<List<BaseMessage>>> fetchNextMessages({...});
  Future<Result<void>> markAsRead(BaseMessage message);
  Future<Result<void>> markAsDelivered(BaseMessage message);
  Future<Result<User?>> getLoggedInUser();
  Future<Result<Conversation>> getConversation({...});
  Future<Result<Conversation>> markMessageAsUnread(BaseMessage message);
}

3. Wiring via the Service Locator

The service locators are the injection point. Both are singletons with a setup() method. Call reset() first, then setup() with your custom implementations before the widget mounts.

Datasource-level override (Conversations)

Dart

class MyConversationsRemoteDataSource implements ConversationsRemoteDataSource {
  @override
  Future<List<Conversation>> getConversations({int limit = 30, String? fromId}) async {
    // Your REST API call, mock data, etc.
  }
  // ... implement remaining methods
}

// Before mounting CometChatConversations:
await ConversationsServiceLocator.instance.reset();

final remote = MyConversationsRemoteDataSource();
final local = ConversationsLocalDataSourceImpl(); // keep default cache
final repo = ConversationsRepositoryImpl(
  remoteDataSource: remote,
  localDataSource: local,
);

Repository-level override (Message List)

Dart

class MyMessageListRepository implements MessageListRepository {
  @override
  Future<Result<List<BaseMessage>>> getMessages({...}) async {
    // Custom logic
  }
  // ...
}

// Before mounting CometChatMessageList:
await MessageListServiceLocator.instance.reset();
// Wire your repo into use cases and pass to the BLoC

Key Points

Point	Detail
`reset()`	Sets `_isInitialized = false` — always call before re-wiring
`setup()`	Guarded by `_isInitialized` — safe to call multiple times normally
`localDataSource` in `MessageListRepositoryImpl`	Optional — pass `null` to disable caching entirely
Fallback caching	`ConversationsRepositoryImpl` falls back to local cache when remote fails — your custom remote inherits this if you use `ConversationsRepositoryImpl` with a custom datasource
`Result<T>`	All repository methods return `Result<T>` (`Success`/`Failure`) — your implementations must do the same

​Configuring Data Fetching with RequestBuilders

​Request Builder by Component

​Providing a Custom BLoC

​BLoC Parameters by Component

​Extending the Default BLoC

​ListBase Hooks

​Component-Specific BLoC Events

​Lifecycle Callbacks

​Related

​Repository & Datasource Overrides

​1. Datasource Override

​Conversations

​Message List

​2. Repository Override

​Conversations

​Message List

​3. Wiring via the Service Locator

​Datasource-level override (Conversations)

​Repository-level override (Message List)

​Key Points

Configuring Data Fetching with RequestBuilders

Request Builder by Component

Providing a Custom BLoC

BLoC Parameters by Component

Extending the Default BLoC

ListBase Hooks

Component-Specific BLoC Events

Lifecycle Callbacks

Related

Repository & Datasource Overrides

1. Datasource Override

Conversations

Message List

2. Repository Override

Conversations

Message List

3. Wiring via the Service Locator

Datasource-level override (Conversations)

Repository-level override (Message List)

Key Points