Create empty C# event handlers automatically

Question

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?

Answer 1

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#?)

Answer 2

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 ); } }