Action<T> vs delegate event

c# delegates
Bhaskar picture Bhaskar · Feb 17, 2010 · Viewed 58.7k times · Source

I have seen developers using the below codes quite alternatively. What is the exact difference between these, and which ones go by the standard? Are they same, as Action and Func<T> is a delegate as well:

public event Action<EmployeeEventAgs> OnLeave;
public void Leave()
{
    OnLeave(new EmployeeEventAgs(this.ID));
}

VS

public delegate void GoOnLeave(EmployeeEventAgs e);
public event GoOnLeave OnLeave;
public void Leave()
{
    OnLeave(new EmployeeEventAgs(this.ID));
}

Answer

Hans Passant picture Hans Passant · Feb 17, 2010

Fwiw, neither example uses standard .NET conventions. The EventHandler<T> generic should declare the event:

public event EventHandler<EmployeeEventArgs> Leave;

The "On" prefix should be reserved for a protected method that raises the event:

protected virtual void OnLeave(EmployeeEventArgs e) {
    var handler = Leave;
    if (handler != null) handler(this, e);
}

You don't have to do it this way, but anybody will instantly recognize the pattern, understand your code and know how to use and customize it.

And it has the great advantage of not being forced to choose between a custom delegate declaration and Action<>, EventHandler<> is the best way. Which answers your question.

Related questions

Pass Method as Parameter using C#

I have several methods all with the same parameter types and return values but different names and blocks. I want to pass the name of the method to run to another method that will invoke the passed method. public int …

Read More
When & why to use delegates?

I'm relatively new in C#, & I'm wondering when to use Delegates appropriately. they are widely used in events declaration, but when should I use them in my own code and why are they useful? why not to use something …

Read More
Func vs. Action vs. Predicate

With real examples and their use, can someone please help me understand: When do we need a Func<T, ..> delegate? When do we need an Action<T> delegate? When do we need a Predicate<T&…

Read More