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Send a Typing Indicator

In other words, as a sender, how do I let the recipient(s) know that I’m typing?

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Start Typing

You can use the startTyping() method to inform the receiver that the logged-in user has started typing. The receiver will receive this information in the onTypingStarted() method of the CometChatMessageDelegate protocol conformance. In order to send the typing indicator, you need to use the TypingIndicator class. 
let typingIndicator = TypingIndicator(receiverID: "receiverUID", receiverType: .user)

CometChat.startTyping(indicator: typingIndicator)

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Stop Typing

You can use the endTyping() method to inform the receiver that the logged-in user has stopped typing. The receiver will receive this information in the onTypingEnded() method of the CometChatMessageDelegate protocol conformance. In order to send the typing indicator, you need to use the TypingIndicator class. 
let typingIndicator = TypingIndicator(receiverID: "receiverUID", receiverType: .user)

CometChat.endTyping(indicator: typingIndicator)
Custom DataYou can use the metaData field of the TypingIndicator class to pass additional data along with the typing indicators. A metaData field is a dictionary and this property can be set from TypingIndicator class. This data will be received at the receiver end and can be obtained using the metaData property.

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Real-time Typing Indicators

In other words, as a recipient, how do I know when someone is typing? You will receive the typing indicators in the onTypingStarted() and the onTypingEnded() method of the CometChatMessageDelegate. In order to receive typing indicators, you must add protocol conformance CometChatMessageDelegate. 
extension ViewController: CometChatMessageDelegate {

  func onTypingStarted(_ typingDetails : TypingIndicator) {

    print("Typing started received successfully")
  }

  func onTypingEnded(_ typingDetails : TypingIndicator) {

    print("Typing ended received successfully")
  }
}
The TypingIndicator class consists of the below parameters:
ParameterInformation
senderAn object of the User class holding all the information. related to the sender of the typing indicator.
receiverIdunique Id of the receiver. This can be the Id of the group or the user the typing indicator is sent to.
receiverTypeThis parameter indicates if the typing indicator is to be sent to a user or a group. The possible values are: 1. CometChat.ReceiverType.user 2. CometChat.ReceiverType.group
metaDataA Dictionary to provide additional data