Write your own C# events

25 April 2015

Every other guide is too long! So this one is as much for my own reference as anyone else’s. Let’s go!

We have:

• A class which owns (and fires) the event, say, “Owner”;
• Some class which handles the event, say, “App”.

1. Write an EventArgs class

Shift+Alt+C to add a new class to the project, and make something like this:

public class SomeEventArgs : EventArgs
{
	// Add fields if you need them
    public string Text { get; set; }
	
	// Add an initialiser if you need one
    public SomeEventArgs(string text)
    {
        Text = text;
    }
}

2. Write a delegate in Owner

Just before your class declaration of Owner in Owner.cs:

public delegate void SomeEventHandler(object sender, SomeEventArgs e);

3. Declare the event in Owner

public class Owner
{
	// I'm the class that owns and fires the event, hi!
	public event SomeEventHandler SomeEvent;
	
	// The rest of the class code
	// ...
}

4. Create a void which fires the event in Owner

You don’t have to do this, but it makes your events more portable; you can extract them to a base class later and preserve the ability to call them from inheriting classes. Set the protection level (public/protected/…) appropriately.

public virtual void OnSomeEvent(SomeEventArgs e)
{
	// This fires the event with the passed args,
	// and a reference to this Owner instance which fired it
	SomeEvent(this, e);
}

5. Fire your event somewhere in Owner

You made the event for a reason, you probably know where you want to fire it. Just call OnSomeEvent(new SomeEventArgs()) or add data to your args using a longer constructor if needed.

6. Write a handler in App

private void EventOwner_EventHappened(Object sender, SomeEventArgs e)
{
	// Handle the event
}

7. Attach the handler in App

var EventOwner = new Owner();
EventOwner.SomeEvent += new SomeEventHandler(EventOwner_EventHappened);

It’s quite a long process but that’s everything.
I hope it helps you out!

Written 2015-04-21