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Join a Group

In order to start participating in group conversations, you will have to join a group. You can do so using the joinGroup() method. 
let guid = "cometchat-guid-11";
let password = nil; // mandatory in case of password protected group type

CometChat.joinGroup(GUID: guid, groupType: .public, password: nil, onSuccess: { (group) in

  print("Group joined successfully. " + group.stringValue())

}) { (error) in

  print("Group joining failed with error:" + error!.errorDescription);
}
The joinGroup() method takes four parameters
ParameterDescription
GUIDThe GUID of the group you would like to join
groupTypeType of the group. CometChat provides 3 types of groups viz. .public .private .password
passwordThe password is mandatory in case of a .password protected the group.
Once you have joined a group successfully, you can send and receive messages in that group. CometChat keeps a track of the groups joined and you do not need to join the group every time you want to communicate in the group. You can identify if a group is joined using the hasJoined parameter in the Group object.

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Real-time Group Member Joined Events

In other words, as a recipient, how do I know when someone joins a group? To receive Real-Time Events for the same, you need to implement the onMemberAddedToGroup() method of the GroupListener class. 
extension AppDelegate: CometChatGroupDelegate {

  func onMemberAddedToGroup(action: ActionMessage, addedBy: User, addedUser: User, addedTo: Group) {
      //When any member is added in the group this function will be called
  }

}

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Missed Group Member Joined Events

In other words, as a member of a group, how do I know if someone joins the group when my app is not running? When you retrieve the list of previous messages if a member has joined any group that the logged-in user is a member of, the list of messages will contain an Action message. An Action message is a sub-class of BaseMessage class. For the group member joined the event, in the Action object received, the following fields can help you get the relevant information-
  1. action - joined
  2. actionBy - User object containing the details of the user who joined the group
  3. actionFor - Group object containing the details of the group the user has joined