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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. 
String GUID = "GUID";
String groupType = CometChatGroupType.public;
String password = "";

CometChat.joinGroup(GUID, groupType, password: password,
                  onSuccess: (Group group) {
                    debugPrint("Group Joined Successfully : $group ");
                  }, onError: (CometChatException e) {
                    debugPrint("Group Joining failed with exception: ${e.message}");
  });
The joinGroup() method takes the below parameters
ParameterDescription
GUIDThe GUID of the group you would like to join
groupTypeType of the group. CometChat provides 3 types of groups viz. 1.CometChatGroupType.public (public). 2.CometChatGroupType.password (password) 3.CometChatGroupType.private (private)
passwordPassword is mandatory in case of a password protected 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 everytime 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 member of a group, how do I know if someone joins the group when my app is running? If a user joins any group, the members of the group receive a real-time event in the onGroupMemberJoined() method of the GroupListener class. 
class Class_Name  with GroupListener {

//CometChat.addGroupListener("group_Listener_id", this);
@override
void onGroupMemberJoined(Action action, User joinedUser, Group joinedGroup) {
  debugPrint("onGroupMemberJoined");
}

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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 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