Problem: C# custom event is null

[CodeBlue]

Hi,

(these are sample classes to illustrate)


I have 3 classes:


public class A
{
....
//array of 4 B objects
public B[4] B_Obj;
public A()
{
B_Obj = new B[4];
for (int i=0; i<4; i++)
B_Obj[i] = new B();



}


public class B
{
public delegate void MyDelegate(int i);
public event MyDelegate OnFire;

public void ChangeValue(int x)
{
if (OnFire != null)
OnFire(x);
}


public class C
{
public A[] a = new A[10];


public C()
{
for (int x=0; x < 10; x++)
{
//init the A objects
A[x] = new A();
for (int y=0; y<4; y++)
{
//link all the B object events to one method
A[x].B_Obj [y].OnFire += new B.MyDelegate(B_ Event_Raised);

}
}


//try to fire the event
A[0].B_Obj[0].ChangeValue(1) ;


}//end C constructor


public void B_Event_Raised( int x)
{
....
}


}


///////////////////////////////////////////////

However, in the above code, B_Event_Raised never gets called, and the
OnFire event always returns null. How come this is the case, when the
event handler is linked in C???


Regards,


Alex

[Mark R. Dawson]

RE: Problem: C# custom event is null

Hi CodeBlue,
your code works just as epxected when I ran it, the B_event_raised method
is getting called. Here is your code modified to compile from the original
example:

using System;
using System.Collecti ons.Generic;
using System.Text;

namespace ConsoleApplicat ion19
{
class Program
{
static void Main(string[] args)
{
C c = new C();
}
}


public class A
{
//array of 4 B objects
public B[] B_Obj;
public A()
{
B_Obj = new B[4];
for (int i = 0; i < 4; i++)
B_Obj[i] = new B();



}
}


public class B
{
public delegate void MyDelegate(int i);
public event MyDelegate OnFire;

public void ChangeValue(int x)
{
if (OnFire != null)
OnFire(x);
}
}


public class C
{
public A[] a = new A[10];


public C()
{
for (int x = 0; x < 10; x++)
{
//init the A objects
a[x] = new A();
for (int y = 0; y < 4; y++)
{
//link all the B object events to one method
a[x].B_Obj[y].OnFire += new B.MyDelegate(B_ Event_Raised);

}
}


//try to fire the event
a[0].B_Obj[0].ChangeValue(1) ;


}//end C constructor


public void B_Event_Raised( int x)
{

}
}

}


Mark Dawson

http://www.markdawson.org

"CodeBlue" wrote:
[color=blue]
> Hi,
>
> (these are sample classes to illustrate)
>
>
> I have 3 classes:
>
>
> public class A
> {
> ....
> //array of 4 B objects
> public B[4] B_Obj;
> public A()
> {
> B_Obj = new B[4];
> for (int i=0; i<4; i++)
> B_Obj[i] = new B();
>
>
>
> }
>
>
> public class B
> {
> public delegate void MyDelegate(int i);
> public event MyDelegate OnFire;
>
> public void ChangeValue(int x)
> {
> if (OnFire != null)
> OnFire(x);
> }
>
>
> public class C
> {
> public A[] a = new A[10];
>
>
> public C()
> {
> for (int x=0; x < 10; x++)
> {
> //init the A objects
> A[x] = new A();
> for (int y=0; y<4; y++)
> {
> //link all the B object events to one method
> A[x].B_Obj [y].OnFire += new B.MyDelegate(B_ Event_Raised);
>
> }
> }
>
>
> //try to fire the event
> A[0].B_Obj[0].ChangeValue(1) ;
>
>
> }//end C constructor
>
>
> public void B_Event_Raised( int x)
> {
> ....
> }
>
>
> }
>
>
> ///////////////////////////////////////////////
>
> However, in the above code, B_Event_Raised never gets called, and the
> OnFire event always returns null. How come this is the case, when the
> event handler is linked in C???
>
>
> Regards,
>
>
> Alex
>
>[/color]

[Jon Skeet [C# MVP]]

Re: Problem: C# custom event is null

CodeBlue <minimaximus@gm ail.com> wrote:[color=blue]
> (these are sample classes to illustrate)[/color]

<snip>
[color=blue]
> However, in the above code, B_Event_Raised never gets called, and the
> OnFire event always returns null. How come this is the case, when the
> event handler is linked in C???[/color]

Well, it looks okay to me.

Could you post a short but *complete* program which demonstrates the
problem?

See http://www.pobox.com/~skeet/csharp/complete.html for details of
what I mean by that.

--
Jon Skeet - <skeet@pobox.co m>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
If replying to the group, please do not mail me too

[CodeBlue]

Re: Problem: C# custom event is null

Thanks Jon and Mark,

As your "Short but Complete" page says Jon, after I put the program in
the compiler, I immediately saw the difference from my original
program, and I felt foolish to have asked the question (hey, it was 4
am) ;)

The problem is that I was calling the ChangeValue function on a
different B_Obj, not the one I added the event handler for.

Best Regards,

Alex