C# – downside to adding an anonymous empty delegate on event declaration

c++coding-styledelegateseventsidioms

I have seen a few mentions of this idiom (including on SO):

// Deliberately empty subscriber
public event EventHandler AskQuestion = delegate {};

The upside is clear – it avoids the need to check for null before raising the event.

However, I am keen to understand if there are any downsides. For example, is it something that is in widespread use and is transparent enough that it won't cause a maintenance headache? Is there any appreciable performance hit of the empty event subscriber call?

Best Solution

Instead of inducing performance overhead, why not use an extension method to alleviate both problems:

public static void Raise(this EventHandler handler, object sender, EventArgs e)
{
    if(handler != null)
    {
        handler(sender, e);
    }
}

Once defined, you never have to do another null event check again:

// Works, even for null events.
MyButtonClick.Raise(this, EventArgs.Empty);

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C# – Create empty C# event handlers automatically

I saw this on another post and have shamelessly stolen it and used it in much of my code ever since:

public delegate void MyClickHandler(object sender, string myValue);
public event MyClickHandler Click = delegate {}; // add empty delegate!

//Let you do this:
public void DoSomething() {
    Click(this, "foo");
}

//Instead of this:
public void DoSomething() {
    if (Click != null) // Unnecessary!
        Click(this, "foo");
}

* If anyone knows the origin of this technique, please post it in the comments. I really do believe in the source getting due credit.

(Edit: I got it from this post Hidden Features of C#?)

C# – Anonymous delegate

There's no such thing as an "anonymous delegate" (or rather, that's not a recognised term in the C# specification, or any other .NET-related specification I'm aware of).

There are anonymous functions which include anonymous methods and lambda expressions.

Your code shows plain old anonymous methods - although they are using the one feature lambda expressions don't have: the ability to not express the parameters at all when you don't care about them.

Best Solution

Related Solutions

C# – Create empty C# event handlers automatically

C# – Anonymous delegate

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