ScarceEventSource.cs

namespace Events;

public class ScarceEventSource
{
    // One dictionary shared by all instances of this class,
    // tracking all handlers for all events.
    // Beware of memory leaks - this code is for illustration only.
    private static readonly
     Dictionary<(ScarceEventSource, object), EventHandler> _eventHandlers
      = new();

    // Objects used as keys to identify particular events in the dictionary.
    private static readonly object EventOneId = new();
    private static readonly object EventTwoId = new();


    public event EventHandler EventOne
    {
        add => AddEvent(EventOneId, value);
        remove => RemoveEvent(EventOneId, value);
    }

    public event EventHandler EventTwo
    {
        add => AddEvent(EventTwoId, value);
        remove => RemoveEvent(EventTwoId, value);
    }

    public void RaiseBoth()
    {
        RaiseEvent(EventOneId, EventArgs.Empty);
        RaiseEvent(EventTwoId, EventArgs.Empty);
    }

    private (ScarceEventSource, object) MakeKey(object eventId) => (this, eventId);

    private void AddEvent(object eventId, EventHandler handler)
    {
        var key = MakeKey(eventId);
        _eventHandlers.TryGetValue(key, out EventHandler? entry);
        entry += handler;
        _eventHandlers[key] = entry;
    }

    private void RemoveEvent(object eventId, EventHandler handler)
    {
        var key = MakeKey(eventId);
        EventHandler? entry = _eventHandlers[key];
        entry -= handler;
        if (entry == null)
        {
            _eventHandlers.Remove(key);
        }
        else
        {
            _eventHandlers[key] = entry;
        }
    }

    private void RaiseEvent(object eventId, EventArgs e)
    {
        var key = MakeKey(eventId);
        if (_eventHandlers.TryGetValue(key, out EventHandler? handler))
        {
            handler(this, e);
        }
    }
}