如何订阅多个事件

Question

I have a UserGroup object that has a property: List of User objects. Each User object raises particular event. I want to be able to handle this event from all Users in UserGroup .

For example:

public abstract class User : IUser
{
    public event EventHandler<MatchCompletedEventArgs> MatchCompleted;

    public bool Match(Job job)
    {
        bool result = UserMatch(job);

        EventHandler<MatchCompletedEventArgs> handler = MatchCompleted;
        handler?.Invoke(this, new MatchCompletedEventArgs(result));

        return result;
    }

    protected abstract bool UserMatch(Job job);
}


public class UserGroup
{
    public int Id { get; set; }
    public string Name { get; set; }
    public List<IUser> Users { get; set; }

    public UserGroup(int id, string name)
    {
        Id = id;
        Name = name;
        Users = new List<IUser>();
    }

    public void AddUser(IUser user)
    {
        // TODO:
        // In here I want to subscribe to user.MatchCompleted event 
        // Eventually I want to be able to handle MatchCompleted event in all users in the list

        Users.Add(user);
    }

    public void OnMatchCompleted()
    {
        // TODO:
        // Whenever, any of the users throws MatchCompleted completed event I need to store complex informations about the Match process,
        // Ideally in one place, like this function.
    }

    public bool Match(Job job)
    {
        // Match will return TRUE only if all users will match it
        foreach (var user in Users)
        {
            if (!user.Match(job)) return false;
        }
        return true;
    }
}

These two "TODO" in the code is what I'm looking for.

How can I catch an event that can be raised by multiple objects stored in one list?

Answer 1

You can subcribe to the event for each User object in the method which is pretty straightforward:

public void AddUser(IUser user)
{
    user.MatchCompleted  += OnMatchCompleted; // subscribed event for each user       
    Users.Add(user);
}

and your event would look like:

public void OnMatchCompleted(object sender,MatchCompletedEventArgs e)
{   
    User user = sender as User;   // will work fine
    IUser iUser = sender as IUser; // this will also work

   // now you can use user information
   // write your complex logic here
}

Now this way OnMatchCompleted will be called for every user in the collection of Users as we subscribed for each of them.