Re: Unregistering Event - C# Discussion Boards

stancrm26-Apr-07 2:54

stancrm

26-Apr-07 2:54

GridVoucher.Click -= new GridClickEventHandler(GridVoucher_Click);

Nouman Bhatti26-Apr-07 3:07

Nouman Bhatti

26-Apr-07 3:07

You don't have to worry about.. deallocating the memory.
the GC will do it for your self.

otherwise if u still want to do it.. then u don't need to unregister the event

and if u still want to unregister the event then the -= is the operator to do that.

Rome'26-Apr-07 3:47

Rome'

26-Apr-07 3:47

Thanks Guys for your prompt reply Smile | :)

Just one doubt remains...??!!!

Now i dispose off the control which was subscribing the event. But if the event it self isnt unregistered first will that result in a reference to this event still remaining in memory even though the subscriber has been de-allocated

Ot will the GC take care of that too...

Just thinking out aloud...

Romi

Scott Dorman26-Apr-07 4:02

26-Apr-07 4:02

Deallocating memory and unregistering event handlers are not the same thing. The proper way to handle this is unregister the event handler inside your own Dispose method, which involves properly implementing the Dispose pattern.

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Scott Dorman26-Apr-07 4:12

26-Apr-07 4:12

The proper way to do this is to place the code to unregister the event handler in the Dispose method.

I'm going to assume that GridVoucher is not a custom control, user control, or form, and is, instead, a standard UI control (like a listbox). That being said, the form (or user control) that contains this control will have a Dispose method (if you are using VS2005, look in the .Designer.cs file for it). This method should look something like this:

protected override void Dispose(bool disposing)
{
   if (disposing && (components != null))
   {
      components.Dispose();
   }
   base.Dispose(disposing);
}

You need to modify this method to look similar to this:

protected override void Dispose(bool disposing)
{
   if (disposing && (components != null))
   {
      components.Dispose();
   }
 
   if (disposing)
   {
      if (GridVoucher != null)
      {
         GridVoucher.Click -= GridVoucher_Click;
      }
   }
   base.Dispose(disposing);
}

What this does is tell the Garbage Collector (GC) that when the form (or user control) is disposed (and not running as part of a finalizer, which is another part of the garbage collection process) that it also needs to remove the event handler if the GridVoucher object exists and is not null.

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In just two days, tomorrow will be yesterday.

Rome'26-Apr-07 4:43

Rome'

26-Apr-07 4:43

Scott Hi !! Smile | :)

Thanks for your reply !!

Yeah ur right GridVoucher is a third Party unbound Grid !!..

Just some more questions come to mind !!

Yeah i realize i will have to put it into the dispose method of the form in which i have created GridVoucher (thats another issue that every time i change the form one bit... the designer code will be regenerated.. Sigh | :sigh:

probably i can inherit from a base form in which i can define dispose interface)

But i need to unregister this event on the fly..since the control i am creating is on the fly...

Will writing this statement

GridVoucher.Click -= new (GridVoucher_Click); be enough

i mean i can understand it when we say += new (gridvoucher_click) but will

-= new (GridVoucher_Click) also work..??? WTF | :WTF:

i mean i am creating a new instance of the event handler here and unregistering it also..

is that ok..?

Thanks Scott once again

Romi

Scott Dorman26-Apr-07 5:16

26-Apr-07 5:16

Rome` wrote:
the designer code will be regenerated

If you are using VS2005, it is safe to modify the Dispose method in the .Designer.cs file. Otherwise, you are right and may have an issue (it's been too long since I've used the earlier versions so I'm not 100% sure if they will overwrite the Dispose method when regenerating the designer generated code).

Rome` wrote:
GridVoucher.Click -= new (GridVoucher_Click); be enough

If you double check the code in my previous post, you will see that I am actually calling GridVoucher.Click -= GridVoucher_Click;. There is no new call. Technically, the GridVoucher.Click -= new(GridVoucher_Click); is creating a new event handler delegate with the same signature as the previous one and then unregistering it, which ultimately causes both to be unregistered. It's a little bit quirky that you can do this, but it does work. However, the better approach is to use the GridVoucher.Click -= GridVoucher_Click; syntax as this prevents an additional object from being created. Remember, this is all happening as the class is being disposed, so you want to make sure things happen as quickly and efficiently as possible. You should avoid creating new objects inside the Dispose whenever possible.

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Dan Neely26-Apr-07 8:50

Dan Neely

26-Apr-07 8:50

Scott Dorman wrote:
If you are using VS2005, it is safe to modify the Dispose method in the .Designer.cs file. Otherwise, you are right and may have an issue (it's been too long since I've used the earlier versions so I'm not 100% sure if they will overwrite the Dispose method when regenerating the designer generated code).

I know VS03 doesn't touch dispose within a form after the initial creation, so I'd assume it's safe for a control as well.

--
C^{le^aK}O The sad part about this instance is that none of the users ever said anything [about the problem].

Pete O`Hanlon Doesn't that just tell you everything you need to know about users?

Martin#6-May-07 20:31

6-May-07 20:31

Hello Scott,

As I read this post two weeks ago, I was really impressed about the possiblity to unregister events without instanciating a new event handler delegate. (So I voted "5" for it)

I now whanted to test it in my application with a System.Windows.Forms.Timer.Tick event and found out that it's not compiling. Confused | :confused:

I'm using VS2003 .Net1.1!

tmrSession.Tick -= new EventHandler(tmrSession_Tick); //compiles fine

tmrSession.Tick -= tmrSession_Tick; //error: blablabla... usage without quotation mark

tmrSession.Tick -= "tmrSession_Tick"; //does of course not compile and makes no sence at all. (string confersion to ...)

Hope you can help me out!
Thanks for your time and help!

All the best,

Martin

Scott Dorman7-May-07 4:21

7-May-07 4:21

Martin,

Can you provide the actual error message? I don't have access to VS2003 anymore, but this syntax should work.

Adding the event handler should be tmrSession.Tick += new EventHandler(tmrSession_Tick); and removing the event handler should be tmrSession.Tick -= tmrSession_Tick;

It is possible that .NET 1.1 didn't support this syntax, but I don't think that is likely since this is really just delegate management and I don't think the underlying architecture changed much between .NET 1.1 and 2.0.

Scott.

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Martin#7-May-07 4:38

7-May-07 4:38

Hello Scott,

Thanks again for your time!

I only have German version of VS2003, so I have to tranclate it in my words. Unsure | :~

There is a reference on the method 'tmrSession_Tick(object, System.EventArgs)' without the usage of quotation marks!

Regards

Martin

Scott Dorman7-May-07 4:42

7-May-07 4:42

Could you post (or email) the relevant snippets of code? Even though I don't have VS2003 anymore, I might be able to see if the code looks correct. I verified with the System.Windows.Forms.Timer object that I can do the following with VS2005:

this.timer1.Tick += new EventHandler(timer1_Tick);
this.timer1.Tick -= timer1_Tick;

Thanks,

Scott.

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Martin#7-May-07 4:48

7-May-07 4:48

Hello Scott,

Thanks for your quick answer and interest.
But I did exactly the same you posted and failed at compilation like posted before.

I don't whant to waste your time anymory, but I'm really thankfull that you tried to help me.
I relly think now that VS2003 doesn't support this feature!

May I have a quick look at google.

All the best,

Martin

Scott Dorman7-May-07 4:51

7-May-07 4:51

Martin,

It does sound like VS2003 does not support this syntax. Sorry I wasn't able to help you resolve the problem, but it certainly wasn't wasting my time. If you are able to find out if this syntax works I would definately like to know.

Thanks,

Scott.

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In just two days, tomorrow will be yesterday.

Martin#7-May-07 4:54