Why would a 'public event EventHandler cccc' be null?

Answer 1

If you haven't hooked any event subscribers up to your StartedWorking event, then it will be null. That is how .NET events works.

This article, among other things, demonstrates that you should check for null before invoking an event. This other question and answer demonstrates how you can create events in a way that avoids the null check (basically by adding an empty handler always).

Answer 2

The event handler will be null unless somebody has subscribed to the event. As soon as a delegate is subscribed to the event, it will no longer be null.

This is why it's always suggested to use the following form for raising events:

public void Start()
{
    var handler = this.StartedWorking;
    if (handler != null)
    {
         handler(this, eventArgObject);
    }
}

This protects you from a null exception if there has been no subscribers.

Answer 3

Don't you need to assign a function ?

StartedWorking += new EventHandler(afunction);

void afunction(object sender, EventArgs e)
{
   DoSomething();
}

Answer 4

As others have already said, it's null because there are no subscribers.

To answer your edit: Yes, you should always check an event for null before triggering it. However, if you just do a plain if(StartedWorking != null){...} you risk a race condition, because it's possible for a subscriber to unsubscribe after the null check but before you trigger the event. Because of this, you should always use this pattern when checking events for null:

protected void OnStartedWorking()
{
    EventHandler localEvent = StartedWorking
    if(localEvent != null)
    {
        localEvent(this, EventArgs.Empty);
    }
}

This prevents the race condition by taking a copy of the event first so the subscribe list is fixed at the point of copying.

There's more infomration about publishing events on MSDN: How to Publish Events that Conform to .NET Framework Guidelines

_{(This works because in .net the MultiCastDelegate class in imutable, so any attempt to change the subscriber list on the event won't effect the copy you have made)}