IMessageCallback

IMessageCallback is an interface used in messaging software to receive asynchronous notifications about message-related events. Implementers provide the logic to handle events such as arrival of new messages, delivery status updates, and read receipts. The interface is typically implemented by client applications and registered with a messaging service or transport layer so that the service can invoke callbacks on the appropriate thread or executor.

Common usage involves a set of callback methods that the messaging layer calls in response to events. For example, onMessageReceived is typically invoked when a new message arrives from a remote user or service. Other callbacks may report delivery status for sent messages (such as onMessageDelivered) or read status (such as onMessageRead). Some designs include onMessageFailed to report delivery or processing errors, and may offer callbacks related to typing indicators or presence updates. The exact method names and signatures are not standardized and vary by platform or SDK, but the intent is to propagate message-related events to the consumer.

Implementation considerations include threading and synchronization, since callbacks may be invoked on background threads. Implementers should marshal updates to the appropriate thread, particularly when updating user interfaces. Error handling within callbacks should be robust, avoiding exceptions that could disrupt the messaging service. Performance considerations suggest keeping callbacks lightweight and avoiding expensive work on callback threads. Security concerns may require filtering data exposure to authorized contexts.

Relation to design patterns: IMessageCallback exemplifies the observer pattern, where the messaging service acts as the subject and the client application as the observer. It is often used alongside other interfaces such as IMessageSender or IMessageService to form a complete messaging workflow.