> Alexandros' reply referred to "delegates".  I had never used one, but=20
> need to do something with a .net SerialPort object, because the=20
> DataReceived event is not on the main thread.  I thought I understood=20
> M$oft VC++ delegates after implementing the example here:=20
> <http://msdn.microsoft.com/en-us/library/zyzhdc6b.aspx>
> Sadly, I don't understand the indirection used in these lines:
>=20
>      delegate void AddListItem();
>      AddListItem^ myDelegate;
>      ...
>      myDelegate =3D gcnew AddListItem( this, &Form1::AddListItemMethod );
>      ...
>      myForm->Invoke( myForm->myDelegate );
>=20
> and trying to invoke the delegate from a class that has no knowledge of=20
> the Form Class is not easy for me.
> --=20

Think of a delegate as a smart function pointer that also knows about the=20
object that holds the function. This means that the function does not need =
to=20
be static.

A delegate is actually a class that holds information about the signature o=
f a=20
function and possibly also about the object where the function is going to =
be=20
invoked. The delegate needs to be instantiated into an object that then tak=
es=20
care of interthread marshalling if needed.

The class invoking the function through the delegate does not need to know=
=20
anything about the class where the function is going to be invoked if it is=
 an=20
object of that class that tells the delegate which function is going to be=
=20
invoked. This is usually the case for Events where the class has a function=
=20
that is to be called at a specific event raised by another object. In this =
case=20
the object is said to subscribe to the event.

For the SerialPort class and the DataReceived event the case is a bit=20
different. Here the DataReceived event is part of a class (perhaps a form o=
r=20
control) but it is running in a separate thread and the delegate needs to b=
e=20
used in order to call another function in the same class but needs to do it=
=20
thread safely. In this case the DataReceived event knows about the class wh=
ere=20
the function is to be invoked since it is part of the same class. Because o=
f=20
this the delegate object can be instantiated by the DataReceived event func=
tion=20
in itself.=20

I usually have my SerialPort class belong to a form with controls (e.g. tex=
t=20
boxes and labels) that is updated with information about the current state =
of=20
the communication. This form is usually invisible and only showed when trou=
ble=20
shooting. When the DataReceive event is raised it needs to use delegates to=
=20
call a function which is running in the GUI thread for that form. The=20
DataReceive event does not call this function until it has received a compl=
ete=20
telegram.

/Ruben
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D
Ruben J=F6nsson
AB Liros Electronic
Box 9124, 200 39 Malm=F6, Sweden
TEL INT +46 40142078
FAX INT +46 40947388
ruben@pp.sbbs.se
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D

--=20
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