NullReference when noone listens

I just finished an MVC implementation for WinForms as a tutorial for whomever and as a walkthrough for myself to see if I could find a nice tidy way to organize my ever increasingly Forms classes. I noticed something I just can't figure out.

When publishing an event that noone subscribes to I get a nullreference exception. There are no way (as I can see) to instantiate the Event in and make sure it's not null so I had to go like this:


1:     public event System.EventHandler ButtonPressed;

2:     

3:     private void btn_Click(object sender, System.EventArgs e)

4:     {

5:     

6:         // if there are no subscribers to the event, it will not have

7:         // been instantiated and calling it will cause a

8:         // nullreference exception. Don't ask me why.

9:         if(ButtonPressed != null)

10:        {

11:            ButtonPressed(this, new System.EventArgs());

12:        }

13:    }

14:    

 

Is this really the only way to do this? Have I missed out about something with publish/subscribe? It should be possible to scream although noone is actually listening..

1 Comment

  • Yep, that is required... the framework SDK mentions it I believe and their examples show the same;





    protected virtual void OnAlarm(AlarmEventArgs e)


    {


    if (Alarm != null)


    {


    //Invokes the delegates.


    Alarm(this, e);


    }


    }


    }





    VB.NET handles it for you as part of raising an event, so if you are looking at VB code you won't see that check...

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