[RESOLVED] Dynamic runtime control event handling

[Kt3]

How can I handle an event for a control that does not yet exist?

[crptcblade]

You would create a generic sub

Private Sub MyEventHandler(ByVal sender As Object, ByVal e As EventArgs)
End Sub

Then use the AddHandler method to attach the control's event to the sub

Dim b As New Button
 
AddHandler b.Click, New EventHandler(AddressOf MyEventHandler)

[Kt3]

Thanks a lot for the info! That's exactly what I'm looking for.

[pax]

Hi.

Just remember to use

RemoveHandler b.Click, New EventHandler(AddressOf MyEventHandler)

when disposing or removing the object.

If you continously create and remove objects, and adding handlers to all of them, you will have a lot of "dead" references taking up memory.

[MrPolite]

Originally posted by pax
Hi.

Just remember to use

RemoveHandler b.Click, New EventHandler(AddressOf MyEventHandler)

when disposing or removing the object.

If you continously create and remove objects, and adding handlers to all of them, you will have a lot of "dead" references taking up memory.

hmmm I think when I was learning these stuff, I read that you dont have to use removehandler. I think when the object disposes, the handles are automatically removed (only if you added the event with addhandler)

[pax]

Originally posted by MrPolite
hmmm I think when I was learning these stuff, I read that you dont have to use removehandler. I think when the object disposes, the handles are automatically removed (only if you added the event with addhandler)

Perhaps you're right. Anyway, the GC will eventually take care of it, but it's still good practice to clean up after yourself.
Just like at home

[MrPolite]

Originally posted by pax
Perhaps you're right. Anyway, the GC will eventually take care of it, but it's still good practice to clean up after yourself.
Just like at home

LOL yeah

umm talking about cleaning event handlers... even though it's not a VB question: in C# when you add an event handler, do you HAVE to remove it before disposing the control? and how the heck do you remove the event?

[pax]

Hi.

Sorry. I don't know C#. I have tried porting a few small classes to VB with some succes.
But when starting from scratch, I'm just as blank as the screen...

[crptcblade]

The opposite of how you added it

//add
this.button1.Click += new System.EventHandler(this.button1_Click);	

//remove
this.button1.Click -= new System.EventHandler(this.button1_Click);

BTW - I'd be willing to bet that the reason the C# forum is slow is because people aren't posting their questions in there.

[MrPolite]

Originally posted by crptcblade
The opposite of how you added it

//add
this.button1.Click += new System.EventHandler(this.button1_Click);	

//remove
this.button1.Click -= new System.EventHandler(this.button1_Click);

BTW - I'd be willing to bet that the reason the C# forum is slow is because people aren't posting their questions in there.

and the reason people don't post their C# questions in the C# forum is because the C# forum is slow
thanks for the reply

[PT Exorcist]

Actually vegeta's code is not right, you can't remove an event handler like that.
If you look carefully you are removing a NEW object event handler and that's not what you want. To remove a handler you'll have to when adding the handler, just save the reference in some place and then just do Class.Event -= mySavedHandler

About this:

If you continously create and remove objects, and adding handlers to all of them, you will have a lot of "dead" references taking up memory.

Well the problem isn't that, the problem is that if you run again the same function that created the handlers in the first place, next time an event should happen it will happen twice...

[crptcblade]

Originally posted by PT Exorcist
Actually vegeta's code is not right, you can't remove an event handler like that.
If you look carefully you are removing a NEW object event handler and that's not what you want. To remove a handler you'll have to when adding the handler, just save the reference in some place and then just do Class.Event -= mySavedHandler

Hmmm...works fine for me

this.button1.Click += new EventHandler(this.ButtonClickHandler);  //somewhere in the form constructor


private void ButtonClickHandler(object sender,EventArgs args)
{
	MessageBox.Show("");
	this.button1.Click -= new EventHandler(this.ButtonClickHandler);
}

The messagebox only shows on the first click.

[tommygrayson]

You would create a generic sub

Private Sub MyEventHandler(ByVal sender As Object, ByVal e As EventArgs)
End Sub

Then use the AddHandler method to attach the control's event to the sub

Dim b As New Button
 
AddHandler b.Click, New EventHandler(AddressOf MyEventHandler)

Hey thanks man! That really helped me a lot.