Here is the code which defines a C# EventHandler, as written in the documentation, it represents the method that will handle an event that has no event data:
// Summary: // Represents the method that will handle an event that has no event data. // // Parameters: // sender: // The source of the event. // // e: // An System.EventArgs that contains no event data. [Serializable] [ComVisible(true)] public delegate void EventHandler(object sender, EventArgs e);
So after declaring a specific event:
private event EventHandler OnSomethingHappened;
We need to write a method to raise this event:
private void RaiseOnSomethingHappened() { if (OnSomethingHappened != null) { OnSomethingHappened(this, new EventArgs()); } }
There is another way to raise events, read about it in A New Pattern For Event Declaration. Anyway, we can define EventArgs as a private member and use it instead of allocating an EventArgs object every time the event is raised. Fortunately, there is no need for that, C# introduce us the EventArgs.Empty! So, this code should look like this:
private void RaiseOnSomethingHappened() { if (OnSomethingHappened != null) { OnSomethingHappened(this, EventArgs.Empty); } }
I have to admit that I had a lot of thoughts wether to write this post or not. I was pretty sure that most of the developers know about that issue and I will only tell the obvious. But after doing a little research, I found out that ~40% of my colleagues didn’t use EventArgs.Empty so I realized that it might be new to some of Dev102 readers too. Please be honest, were you aware of this issue or not?
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JOHN Said on Sep 22, 2008 :
To be honest, whenever I need empty args, I just pass a null.
Works for me.
Matti Lehtinen Said on Sep 23, 2008 :
Great tip! I have always used new EventArgs() without knowing there is a better alternative.
sirrocco Said on Sep 23, 2008 :
I know about the EventArgs.Empty … but I find myself using it on and off.
PS : it depends on - I have no idea what
Rinat Abdullin Said on Sep 23, 2008 :
There is a bit more to the events
http://rabdullin.com/some-tips-on-writing-event-handling-code-in-c-net/
Andrei Rinea Said on Sep 23, 2008 :
I hope I will be believed but I knew about EventArgs.Empty and used it. Although I didn’t find out about it by careful study but Intellisense exploration ( LOLz ) and studying source code from others.
I guess it’s safer than null because you can ellimiate some NullReferenceException caused in client’s code.
sunly Said on Sep 23, 2009 :
Excellent Post!