Question

I have a programming problem which I think is being caused by my rustiness in using events and delegates…

I have the code:

public void DoStuff()
        {
            List<IProcess> processorsForService1  = processorsForService1 = ProcessFactory.GetProcessors();

            foreach (IProcess p in processorsForService1)
            {
                if (p.ProcessTimer != null)
                {
                    p.ProcessTimer.Elapsed += new ElapsedEventHandler(IProcess_Timer_Elapsed);
                }
            }
        }

And:

  private void IProcess_Timer_Elapsed(object sender, ElapsedEventArgs e)
            {
                IProcess p = (IProcess)sender;
                p.Step_One();
                p.Step_Two();
            }

But when I get to the event handler im getting null reference exception for p on the first line.

How do I pass an argument to the handler in this instance?

Answer 1

It looks like you’re using a System.Timers.Timer, if you were to use a System.Threading.Timer then you could pass a state object which, in this case, could be the desired instance of a class, i.e. the timer’s ‘owner’. In this way, you define your method body as with your previous experience of implementation within an event handler, only now the signature is as follows:

private void MyTimerCallbackMethod(object state)
{

}

Then, upon creating the timer instance, you can do something such as:

var timerCallback = new TimerCallback(MyTimerCallback);
var timer = new Timer(timerCallback, myStateObject, 
    Timeout.Infinite, Timeout.Infinite);

Then, use timer.Change(whenToStart, interval) to kick off the timer.