Message Introduction

The IMLib SDK defines the RCMessage class for message transmission and management.

RCMessage Model

The RCMessage class encapsulates the following key data:

• Attributes for message transmission: Sender ID, Receiver ID, conversation type, etc.
• Message Content: Encapsulates the specific content carried by a message, divided into regular message content and media message content. For example, text message content (RCTextMessage) belongs to regular message content, while image message content (RCImageMessage) belongs to media message content. The type of message content, often referred to as the "message type," determines whether to use the interface for sending regular messages or media messages.

tip

The term "message" in the documentation, such as text message, voice message, etc., sometimes refers to the specific content of the message inherited from RCMessageContent or RCMediaMessageContent.

The following table describes the key attributes of the RCMessage class. For a complete list of attributes, refer to the API documentation.

The data structure of RCMessage is as follows:

Attribute Name	Type	Description
objectName	NSString	The identifier name of the message type, determined by the value obtained from the message body class method +getObjectName.
content	RCMessageContent	The specific content carried by the message, which must be a subclass instance of RCMessageContent or RCMediaMessageContent, encapsulating the specific data fields of different types of messages. The IM service provides predefined message types and specifies a cross-platform consistent message content structure (see Message Type Overview), such as text, voice, image, GIF, etc. You can also create custom message types by inheriting RCMessageContent or RCMediaMessageContent.
conversationType	RCConversationType	The conversation type enumeration, such as one-to-one chat, group chat, chatroom, ultra group, system conversation, etc. Refer to Conversation Introduction.
senderUserId	NSString	The user ID of the message sender.
targetId	NSString	The conversation ID (or Target ID), used to identify the other end of the conversation. For one-to-one conversations, the Target ID is the user ID of the other end. Therefore, the Target ID of all sent and received messages must be the user ID of the other end. Note that the Target ID of messages received by the local user in the local message data is not the current user ID, but the user ID of the other end (the message sender). In group, chatroom, ultra group conversations, the Target ID is the corresponding group, chatroom, ultra group ID. For system conversations, since client users cannot reply to system conversation messages, no Target ID is needed.
channelId	NSString	The ultra group channel ID.
messageId	long	The message ID, which is the unique ID of the message in local storage (database index unique value).
messageUId	String	The message UID, globally unique under the same App Key. Only successfully sent messages have a unique ID.
messageDirection	RCMessageDirection	The message direction enumeration, divided into sending and receiving.
sentTime	long long	The message sending time. The sending time is the local time of the server when the message arrives at the server from the sending client. Uses UNIX timestamp in milliseconds.
receivedTime	long long	The message receiving time. The receiving time is the local time of the client when the message arrives at the receiving client. Uses UNIX timestamp in milliseconds.
sentStatus	RCSentStatus	The status of the sent message, such as sending, sent successfully, failed to send, or canceled.
receivedStatusInfo	RCReceivedStatusInfo	The status class of the received message, such as whether it has been read or downloaded. For details, see Message Receiving Status.
readReceiptInfo	RCReadReceiptInfo	The read receipt information for group chat messages. For details, refer to Group Chat Message Receipt.
canIncludeExpansion	BOOL	Whether message expansion is allowed. For details, refer to Message Expansion.
expansionDic	NSDictionary	The message expansion information. For details, refer to Message Expansion.
extra	NSString	Additional information of the message, which is a local operation field and will not be sent to the server. Distinguish from RCMessage.content.extra, which will be sent to the other end along with the message.
isOffLine	BOOL	Whether the message is an offline message, only valid in the callback method for receiving messages. If the message is an offline message, it is YES, otherwise it is NO.
hasChanged	BOOL	Whether the message has been modified, only supported for ultra groups.
directedUserIds	NSArray<NSString *>	The array of user IDs receiving targeted messages.
disableUpdateLastMessage	BOOL	Whether to disable updating to the latest message in the conversation, default is NO: update, YES: do not update.

RCMessageContent

The RCMessage class encapsulates the content attribute, representing the specific content carried by a message. The type of message content must inherit from the following base classes:

• RCMessageContent - Regular message content. For example, the text message content (RCTextMessage) in the SDK's built-in message types inherits from RCMessageContent.
• RCMediaMessageContent - Media message content, inherits from the MessageContent base class and adds logic for handling media files. For example, the image message content (RCImageMessage) in the SDK's built-in message types inherits from MediaMessageContent. When sending and receiving messages, the SDK will determine whether the message type is a media type message. If it is a media type, the upload or download process for media files will be triggered.

The IM service provides predefined, cross-platform consistent message content structures (see Message Type Overview), such as text, voice, image, GIF, etc. If you need to implement custom messages, you can inherit RCMessageContent or RCMediaMessageContent to create custom message content.

Message Storage Strategy

The client SDK and IM server identify the type of message, its storage strategy on the local and server sides, and whether it is counted in the unread message count through the message storage strategy (RCMessagePersistent). The specific content of messages inherited from RCMessageContent or RCMediaMessageContent comply with the RCMessagePersistentCompatible protocol, setting storage-related attributes.

If sending messages of the SDK's built-in message types, RCMessagePersistent is automatically handled by the SDK by default, requiring no additional operations. For the storage strategy of built-in messages, see Message Type Overview.

If you need to create custom message types, note that custom messages must comply with the RCMessagePersistentCompatible protocol. For details, see Custom Message Types.