c# custom event kicking up errors

3 replies. Latest Post by JoBone on January 16, 2009.

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Member

1 points

c# custom event kicking up errors

11-06-2008 7:44 PM |

So, I'm trying to make a custom event for another object to subscribe to. The frustrating thing is that I've done this a couple times already and it's working, but I'm getting an odd error now. Here's some code:

(inside class declaration)

public delegate void SideSwipeHandler(object ob, EventArgs e);
public event SideSwipeHandler SideSwipe;

(inside a method later on)

EventArgs ev2 = new EventArgs();
SideSwipe(this, ev2);

Here's the error that gets triggered when it reaches the event call:

Object reference not set to an instance of an object.

Any thoughts?

bartczer...

Contributor

4160 points

729 Posts

Re: c# custom event kicking up errors

11-06-2008 10:09 PM |

You have to make sure the event has subscribers first. So you can do this a couple ways...

- always define a empty subscriber. This is a real nice solution if you are doing multithreading and can incurr a very small performance penalty on the event. Declare your event like this: public event SideSwipeHandler SideSwipe = delegate { };

This uses an anonymous method to always have one subscriber.

- check the event if it has subscribers always. If you do the above decleration, you do not need to do this bottom:

Instead of this: SideSwipe(this, ev2);

Use this:

if (SideSwipe != null)

{

SideSwipe(this, ev2);

}

Either way is fine..the second solution is not as nice, because if you DO use multiple threads you can run into a race condition.

Please mark as answer if this helped.

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Bart Czernicki
http://www.silverlighthack.com | My new Silverlight and Business Intelligence Book

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