Message overview

The Chat SDK defines the NCMessage class for message transport and management.

NCMessage model

The NCMessage class contains:

• Transport properties: sender user ID, channel identifier (channel type + channel ID), etc.
• Message content: the actual payload, either a regular message content (NCMessageContent) or a media message content (NCMediaMessageContent). For example, NCTextMessage is a regular content type, while NCImageMessage is a media content type.

Key NCMessage properties:

Property	Type	Description
channelIdentifier	NCChannelIdentifier	Channel identifier, containing channel type (channelType) and channel ID (channelId)
messageType	NSString	Message type identifier string
content	NCMessageContent	Message payload — a subclass of NCMessageContent or NCMediaMessageContent
senderUserId	NSString	Sender's user ID
clientId	int64_t	Local database unique ID (locally unique only)
messageId	NSString	Server-assigned globally unique ID (only set after successful send/receive)
direction	NCMessageDirection	Message direction: send or receive
sentTime	int64_t	Server timestamp when sent (milliseconds)
sentStatus	NCSentStatus	Sending status: sending, sent, failed, or cancelled
receivedStatusInfo	NCMessageReceivedStatusInfo	Receiving status: read, listened, downloaded, etc.
metadata	NSDictionary<NSString *, NSString *>	Message extension metadata (key-value pairs)
hasChanged	BOOL	Whether the message has been modified
needReceipt	BOOL	Whether a read receipt is required
sentReceipt	BOOL	Whether the read receipt has been sent
directedUserIds	NSArray<NSString *>	Targeted recipient user IDs (directed message recipients)
disableNotification	BOOL	Whether remote push and local notifications are disabled
disableUpdateLastMessage	BOOL	Whether updating the channel's last message is disabled
isCounted	BOOL	Whether this message is counted toward the unread total
isPersisted	BOOL	Whether this message is persisted locally
isStatusMessage	BOOL	Whether this is a status (transient) message
modifyInfo	NCMessageModifyInfo	Message modification details

NCMessageContent

All message content types inherit from one of two base classes:

• NCMessageContent — regular messages (e.g., NCTextMessage)
• NCMediaMessageContent — media messages with upload/download handling (e.g., NCImageMessage)

The SDK provides predefined cross-platform message types (text, voice, image, GIF, etc.). You can also create custom message types by subclassing these base classes.

Message storage policy

The NCMessagePersistent property controls how messages are stored locally and on the server, and whether they count toward unread message totals. Built-in message types have default storage policies. Custom message types must conform to the NCMessagePersistentCompatible protocol.