How to use sort by in Apex code when using SOSL queries from different tables

Question

Here is the code of the visualforce page:

public class moderatorpanelCtrl
{
    Task tk;
    public list< LoginHistory>  Task {get;set;}
    
    public list< TopicAssignment>  TP {get;set;}
    public list< userActivity>  ua {get;set;}

 
     public moderatorpanelCtrl()
     {
        ua = new list< userActivity>();
        task = [select Id, UserId, LoginTime, NetworkId, Status from LoginHistory where NetworkId = '...'  order by LoginTime desc limit 10];
        for (LoginHistory lh :task){
            userActivity u = new userActivity();
            u.activitydate = lh.LoginTime;
            u.username = lh.UserId;
            u.Status = lh.Status;
            ua.add(u);
        }

        TP = [select Id, NetworkId, TopicId, Topic.Name, Topic.Description, Topic.NetworkId, Topic.CreatedDate, Topic.CreatedById, Topic.CreatedBy.Name, Topic.TalkingAbout, Topic.ManagedTopicType, Topic.SystemModstamp, EntityId, EntityKeyPrefix, 
        EntityType, CreatedDate, CreatedById, IsDeleted, SystemModstamp from TopicAssignment where NetworkId = '...' order by SystemModstamp desc limit 10];
     
    for (TopicAssignment ta :TP){
        userActivity u = new userActivity();
        u.activitydate = ta.SystemModstamp;
        u.username = ta.Topic.CreatedBy.Name;
        u.Status = ta.Topic.Name;
        ua.add(u);
    }
     
    system.debug('list of user activity'+ua);
    //ua.sort();
}

public class userActivity {
    public DateTime activitydate {get;set;}
        public string username {get;set;}
        public string Status {get;set;}
    }
}

Answer 1

Your class userActivity must implement the Comparable interface. This will enable you to call sort().

Presumably, your implementation will use the activitydate field to sort records.