Create empty C# event handlers automatically

It is not possible to fire an event in C# that has no handlers attached to it. So before each call it is necessary to check if the event is null.

if ( MyEvent != null ) {
  MyEvent( param1, param2 );
}

I would like to keep my code as clean as possible and get rid of those null checks. I don't think it will affect performance very much, at least not in my case.

MyEvent( param1, param2 );

Right now I solve this by adding an empty inline handler to each event manually. This is error prone, since I need to remember to do that etc.

void Initialize() {
  MyEvent += new MyEvent( (p1,p2) => { } );
}

Is there a way to generate empty handlers for all events of a given class automatically using reflection and some CLR magic?

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#?)

The notation:

if ( MyEvent != null ) {
  MyEvent( param1, param2 );
}

is not thread safe. You should do it this way:

EventHandler handler = this.MyEvent;
if ( null != handler ) { handler( param1, param2 ); }

I understand, that this is a bother, so you can do helper method:

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

and then call:

RaiseEvent( MyEvent, param1, param2 );

If you are using C# 3.0, you can declare helper method as extension method:

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

and then call:

MyEvent.Raise( param1, param2 );

Also you can create next extension/helper methods for other event handlers. For example:

static void Raise<TEventArgs>( this EventHandler<TEventArgs> handler,
    object sender, TEventArgs e ) where TEventArgs : EventArgs
{
    if ( null != handler ) { handler( sender, e ); }
}

In C# 6.0 there's no need to go to any of these lengths to do the null check, thanks to the conditional null operator ?.

The docs explain that calling MyEvent?.Invoke(...) copies the event to a temporary variable, performs the null check, and if not null, calls Invoke on the temporary copy. This isn't necessarily thread-safe in every sense, as someone could have added a new event after the copy to the temporary variable, which wouldn't be called. It does guarantee you won't call Invoke on null though.

In short:

public delegate void MyClickHandler(object sender, string myValue);
public event MyClickHandler Click;

public void DoSomething() {
    Click?.Invoke(this, "foo");
}

Create empty C# event handlers automatically

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