Error when raising custom event

Question

I have a class that will write a log. The class needs to raise an event (under specific circumstances not indicated below), that will be comsumed by a class to react on it. I have the code below but as soon as I try to raise the event, I get an error on the line as indicated, that

Object reference not set to an instance of an object

Any idea what I'm missing?

//1. Class where event is registered
    public class LogEvent
    {
        public delegate void WriteLogEventHandler(object Sender, WriteLogEventArgs e);
        public event WriteLogEventHandler WriteLog;

        public class WriteLogEventArgs : EventArgs
        {
            public string Message { get; set; }

            public WriteLogEventArgs(string message) : base()
            {
                Message = message;
            }
        }

        //Raise the event.
        internal void OnWriteLog(WriteLogEventArgs e)
        {
             WriteLog(this, e);    //Error here.  Seems like WriteLog is null
        }

//2. Class where event is raised.
public class Logs
{
    public static void WriteLog(string message)
    {
        LogEvent.WriteLogEventArgs args = new LogEvent.WriteLogEventArgs(message);
        new LogEvent().OnWriteLog(args);
    }
}

//3. Class where event should be consumed
public class MyClass()
{
    private LogEvent _logEvent;
    public MyClass()
        {
            //Subscribe to event:
            _logEvent = new LogEvent();
            _logEvent.WriteLog += (sender, args) => { DoSomething(args.Message); };
        }

   public void DoSomething(string message)
   { ... }
}

Answer 1

Two issues:

• You're raising the event whether or not anyone has subscribed to it. Don't do that - you will get a NullReferenceException if you call WriteLog(this, e) when WriteLog is null. In C# 6 it's easy to avoid this:

   WriteLog?.Invoke(this, e); 

• You're subscribing to the event on a different LogEvent instance than the one which is raising the event. This is more of a design issue than anything else - it makes no sense for an individual log event to have a list of subscribers. Instead, you should have a Logger or similar which has the subscribers (via an event), then each LogEvent is passed to those subscribers. You'd create one Logger , subscribe to it, then call WriteLog on the same instance.