Delegates and pointers

**Dave** · Nov 17 '05, 02:04 AM

Re: Delegates and pointers

> callbackEvent Event = delegate()[color=blue]
> {
> MessageBox.Show ("Callback Event Received");
> }[/color]

The above syntax is incorrect.
Treat your callback as a method:

delegate void callbackEvent() ;

void MyCallBack()
{
MessageBox.Show ("Callback Event Received");
}

void ConsumeDelegate ()
{
// Create a pointer to MyCallBack using the callbackEvent signature:
callbackEvent cb = new callbackEvent(M yCallBack);

// Use the method pointer in your interop call:
myAPIregister(c b);

// > The parameter in myAPIregister(p arameter) is
// > expecting a pointer to the callback handler.
//
// .NET Interop will automattically Marshal the delegate you pass to the external method as a pointer to the method
}

--
Dave Sexton
dave@www..jwaon line..com
-----------------------------------------------------------------------
"Wayne Weeks" <Wayne Weeks@discussio ns.microsoft.co m> wrote in message news:35A6F85C-A4DF-4F05-AED1-AC9667C96F4F@mi crosoft.com...[color=blue]
>I am trying to use delegates for the first time and I am probably missing
> something. I have a legacy DLL and I have used DllImport to get to the
> functions that it contains...the normal function calls work fine, but I can't
> get callbacks to work. The delegate declaration etc is below.
>
> public delegate void callbackEvent() ;
>
> callbackEvent Event = delegate()
> {
> MessageBox.Show ("Callback Event Received");
> }
>
>
> The function in the DLL to register the callback is
>
> myAPIregister(E vent);
>
> So I am expecting that myAPIregister(E vent) will provide a pointer to the
> Event delegate. When the callback event occurs it should simply display the
> MessageBox with the text. The parameter in myAPIregister(p arameter) is
> expecting a pointer to the callback handler.
>
> I have done a lot of reading about delegates over the past few days to get
> this far but I appear to be missing something. The Compiler complains that
> the argument is invalid.
>
> Thanks for any help and guidance.[/color]

**Wayne Weeks** · Nov 17 '05, 02:04 AM

Re: Delegates and pointers

Thanks Dave,

I was confused on how to use delegates, but I think I understand how they
are used now. I have used your code as the basis for correcting what I had
done. I still have one final issue that perhaps you may know how to fix.
Here is the code:

delegate void callbackEvent() ;

void MyCallback()
{
MessageBox.Show ("Callback Event Received");
}

private void ptRegisterLinkS tateCallback_Cl ick(object sender, EventArgs e)
{
callbackEvent cb = new callbackEvent(M yCallback);
status = ptAPI.ptRegiste rLinkStateCallb ack(ptHostLinkS tateChange, cb);
MessageBox.Show ("Status = " + status.ToString ());
}

So when the "ptRegisterLink ...." button is clicked a pointer, cb, is created
to MyCallback. The "ptAPI.ptRegist er..." function call is to an external DLL
using DLLImport and I am expecting the 'cb' argument to be the pointer to the
MyCallback method. The code in the DLL is:

public class ptAPI
{
[DllImport("pats api.dll")]
public static extern int ptRegisterLinkS tateCallback(in t callbackID, int
mtdAddress);
}

The compiler complains that there are invalid arguments and that argument 2
'cannot convert from "...Form1.callb ackEvent to int". Clearly I still have
something wrong with my code.

Any ideas as to why this is wrong? Thanks for your help with this, much
appreciated.

Wayne

"Dave" wrote:
[color=blue][color=green]
> > callbackEvent Event = delegate()
> > {
> > MessageBox.Show ("Callback Event Received");
> > }[/color]
>
> The above syntax is incorrect.
> Treat your callback as a method:
>
> delegate void callbackEvent() ;
>
> void MyCallBack()
> {
> MessageBox.Show ("Callback Event Received");
> }
>
> void ConsumeDelegate ()
> {
> // Create a pointer to MyCallBack using the callbackEvent signature:
> callbackEvent cb = new callbackEvent(M yCallBack);
>
> // Use the method pointer in your interop call:
> myAPIregister(c b);
>
> // > The parameter in myAPIregister(p arameter) is
> // > expecting a pointer to the callback handler.
> //
> // .NET Interop will automattically Marshal the delegate you pass to the external method as a pointer to the method
> }
>
> --
> Dave Sexton
> dave@www..jwaon line..com
> -----------------------------------------------------------------------
> "Wayne Weeks" <Wayne Weeks@discussio ns.microsoft.co m> wrote in message news:35A6F85C-A4DF-4F05-AED1-AC9667C96F4F@mi crosoft.com...[color=green]
> >I am trying to use delegates for the first time and I am probably missing
> > something. I have a legacy DLL and I have used DllImport to get to the
> > functions that it contains...the normal function calls work fine, but I can't
> > get callbacks to work. The delegate declaration etc is below.
> >
> > public delegate void callbackEvent() ;
> >
> > callbackEvent Event = delegate()
> > {
> > MessageBox.Show ("Callback Event Received");
> > }
> >
> >
> > The function in the DLL to register the callback is
> >
> > myAPIregister(E vent);
> >
> > So I am expecting that myAPIregister(E vent) will provide a pointer to the
> > Event delegate. When the callback event occurs it should simply display the
> > MessageBox with the text. The parameter in myAPIregister(p arameter) is
> > expecting a pointer to the callback handler.
> >
> > I have done a lot of reading about delegates over the past few days to get
> > this far but I appear to be missing something. The Compiler complains that
> > the argument is invalid.
> >
> > Thanks for any help and guidance.[/color]
>
>
>[/color]

**Dave** · Nov 17 '05, 02:04 AM

Re: Delegates and pointers

No problem.

The declaration for your interop call (external method) should also declare the paramter type as the delegate your passing it:
[color=blue]
> [DllImport("pats api.dll")]
> public static extern int ptRegisterLinkS tateCallback(in t callbackID, callbackEvent CallBack);[/color]

This, of course, means that you have to declare the delegate in your library and not the consuming program.

--
Dave Sexton
dave@www..jwaon line..com
-----------------------------------------------------------------------
"Wayne Weeks" <WayneWeeks@dis cussions.micros oft.com> wrote in message news:A05B408C-E89D-4B96-B8CD-C9F4753158F5@mi crosoft.com...[color=blue]
> Thanks Dave,
>
> I was confused on how to use delegates, but I think I understand how they
> are used now. I have used your code as the basis for correcting what I had
> done. I still have one final issue that perhaps you may know how to fix.
> Here is the code:
>
> delegate void callbackEvent() ;
>
> void MyCallback()
> {
> MessageBox.Show ("Callback Event Received");
> }
>
> private void ptRegisterLinkS tateCallback_Cl ick(object sender, EventArgs e)
> {
> callbackEvent cb = new callbackEvent(M yCallback);
> status = ptAPI.ptRegiste rLinkStateCallb ack(ptHostLinkS tateChange, cb);
> MessageBox.Show ("Status = " + status.ToString ());
> }
>
> So when the "ptRegisterLink ...." button is clicked a pointer, cb, is created
> to MyCallback. The "ptAPI.ptRegist er..." function call is to an external DLL
> using DLLImport and I am expecting the 'cb' argument to be the pointer to the
> MyCallback method. The code in the DLL is:
>
> public class ptAPI
> {
> [DllImport("pats api.dll")]
> public static extern int ptRegisterLinkS tateCallback(in t callbackID, int
> mtdAddress);
> }
>
> The compiler complains that there are invalid arguments and that argument 2
> 'cannot convert from "...Form1.callb ackEvent to int". Clearly I still have
> something wrong with my code.
>
> Any ideas as to why this is wrong? Thanks for your help with this, much
> appreciated.
>
> Wayne
>
> "Dave" wrote:
>[color=green][color=darkred]
>> > callbackEvent Event = delegate()
>> > {
>> > MessageBox.Show ("Callback Event Received");
>> > }[/color]
>>
>> The above syntax is incorrect.
>> Treat your callback as a method:
>>
>> delegate void callbackEvent() ;
>>
>> void MyCallBack()
>> {
>> MessageBox.Show ("Callback Event Received");
>> }
>>
>> void ConsumeDelegate ()
>> {
>> // Create a pointer to MyCallBack using the callbackEvent signature:
>> callbackEvent cb = new callbackEvent(M yCallBack);
>>
>> // Use the method pointer in your interop call:
>> myAPIregister(c b);
>>
>> // > The parameter in myAPIregister(p arameter) is
>> // > expecting a pointer to the callback handler.
>> //
>> // .NET Interop will automattically Marshal the delegate you pass to the external method as a pointer to the method
>> }
>>
>> --
>> Dave Sexton
>> dave@www..jwaon line..com
>> -----------------------------------------------------------------------
>> "Wayne Weeks" <Wayne Weeks@discussio ns.microsoft.co m> wrote in message news:35A6F85C-A4DF-4F05-AED1-AC9667C96F4F@mi crosoft.com...[color=darkred]
>> >I am trying to use delegates for the first time and I am probably missing
>> > something. I have a legacy DLL and I have used DllImport to get to the
>> > functions that it contains...the normal function calls work fine, but I can't
>> > get callbacks to work. The delegate declaration etc is below.
>> >
>> > public delegate void callbackEvent() ;
>> >
>> > callbackEvent Event = delegate()
>> > {
>> > MessageBox.Show ("Callback Event Received");
>> > }
>> >
>> >
>> > The function in the DLL to register the callback is
>> >
>> > myAPIregister(E vent);
>> >
>> > So I am expecting that myAPIregister(E vent) will provide a pointer to the
>> > Event delegate. When the callback event occurs it should simply display the
>> > MessageBox with the text. The parameter in myAPIregister(p arameter) is
>> > expecting a pointer to the callback handler.
>> >
>> > I have done a lot of reading about delegates over the past few days to get
>> > this far but I appear to be missing something. The Compiler complains that
>> > the argument is invalid.
>> >
>> > Thanks for any help and guidance.[/color]
>>
>>
>>[/color][/color]

**Wayne Weeks** · Nov 17 '05, 02:04 AM

Re: Delegates and pointers

OK, thankyou, yes that makes sense, need to make the parameter types the
same. Just one final issue and I hope I can move on with the fun part of
this application. As you note, I added the declaration of the delegate to
the library code as follows:

public class ptAPI
{
delegate void callbackEvent() ;

[DllImport("pats api.dll")]
public static extern int ptRegisterLinkS tateCallback(in t callbackID,
callbackEvent Callback);
}

However when I try to recompile the library the compiler complains that
there is "Inconsiste nt accessibility", parameter type ptAPI.callbackE vent is
less accessibile than ptAPI.ptRegiste rLinkStateCallb ack. Am I missing a
switch for the compiler? Something wrong with declaration of the delegate in
the library. This delegate construct is a tricky thing to grasp....thanks
again, hopefully I can get past this soon.

Wayne

"Dave" wrote:
[color=blue]
> No problem.
>
> The declaration for your interop call (external method) should also declare the paramter type as the delegate your passing it:
>[color=green]
> > [DllImport("pats api.dll")]
> > public static extern int ptRegisterLinkS tateCallback(in t callbackID, callbackEvent CallBack);[/color]
>
> This, of course, means that you have to declare the delegate in your library and not the consuming program.
>
> --
> Dave Sexton
> dave@www..jwaon line..com
> -----------------------------------------------------------------------
> "Wayne Weeks" <WayneWeeks@dis cussions.micros oft.com> wrote in message news:A05B408C-E89D-4B96-B8CD-C9F4753158F5@mi crosoft.com...[color=green]
> > Thanks Dave,
> >
> > I was confused on how to use delegates, but I think I understand how they
> > are used now. I have used your code as the basis for correcting what I had
> > done. I still have one final issue that perhaps you may know how to fix.
> > Here is the code:
> >
> > delegate void callbackEvent() ;
> >
> > void MyCallback()
> > {
> > MessageBox.Show ("Callback Event Received");
> > }
> >
> > private void ptRegisterLinkS tateCallback_Cl ick(object sender, EventArgs e)
> > {
> > callbackEvent cb = new callbackEvent(M yCallback);
> > status = ptAPI.ptRegiste rLinkStateCallb ack(ptHostLinkS tateChange, cb);
> > MessageBox.Show ("Status = " + status.ToString ());
> > }
> >
> > So when the "ptRegisterLink ...." button is clicked a pointer, cb, is created
> > to MyCallback. The "ptAPI.ptRegist er..." function call is to an external DLL
> > using DLLImport and I am expecting the 'cb' argument to be the pointer to the
> > MyCallback method. The code in the DLL is:
> >
> > public class ptAPI
> > {
> > [DllImport("pats api.dll")]
> > public static extern int ptRegisterLinkS tateCallback(in t callbackID, int
> > mtdAddress);
> > }
> >
> > The compiler complains that there are invalid arguments and that argument 2
> > 'cannot convert from "...Form1.callb ackEvent to int". Clearly I still have
> > something wrong with my code.
> >
> > Any ideas as to why this is wrong? Thanks for your help with this, much
> > appreciated.
> >
> > Wayne
> >
> > "Dave" wrote:
> >[color=darkred]
> >> > callbackEvent Event = delegate()
> >> > {
> >> > MessageBox.Show ("Callback Event Received");
> >> > }
> >>
> >> The above syntax is incorrect.
> >> Treat your callback as a method:
> >>
> >> delegate void callbackEvent() ;
> >>
> >> void MyCallBack()
> >> {
> >> MessageBox.Show ("Callback Event Received");
> >> }
> >>
> >> void ConsumeDelegate ()
> >> {
> >> // Create a pointer to MyCallBack using the callbackEvent signature:
> >> callbackEvent cb = new callbackEvent(M yCallBack);
> >>
> >> // Use the method pointer in your interop call:
> >> myAPIregister(c b);
> >>
> >> // > The parameter in myAPIregister(p arameter) is
> >> // > expecting a pointer to the callback handler.
> >> //
> >> // .NET Interop will automattically Marshal the delegate you pass to the external method as a pointer to the method
> >> }
> >>
> >> --
> >> Dave Sexton
> >> dave@www..jwaon line..com
> >> -----------------------------------------------------------------------
> >> "Wayne Weeks" <Wayne Weeks@discussio ns.microsoft.co m> wrote in message news:35A6F85C-A4DF-4F05-AED1-AC9667C96F4F@mi crosoft.com...
> >> >I am trying to use delegates for the first time and I am probably missing
> >> > something. I have a legacy DLL and I have used DllImport to get to the
> >> > functions that it contains...the normal function calls work fine, but I can't
> >> > get callbacks to work. The delegate declaration etc is below.
> >> >
> >> > public delegate void callbackEvent() ;
> >> >
> >> > callbackEvent Event = delegate()
> >> > {
> >> > MessageBox.Show ("Callback Event Received");
> >> > }
> >> >
> >> >
> >> > The function in the DLL to register the callback is
> >> >
> >> > myAPIregister(E vent);
> >> >
> >> > So I am expecting that myAPIregister(E vent) will provide a pointer to the
> >> > Event delegate. When the callback event occurs it should simply display the
> >> > MessageBox with the text. The parameter in myAPIregister(p arameter) is
> >> > expecting a pointer to the callback handler.
> >> >
> >> > I have done a lot of reading about delegates over the past few days to get
> >> > this far but I appear to be missing something. The Compiler complains that
> >> > the argument is invalid.
> >> >
> >> > Thanks for any help and guidance.
> >>
> >>
> >>[/color][/color]
>
>
>[/color]

**Dave** · Nov 17 '05, 02:04 AM

Re: Delegates and pointers

you haven't specified an access modifier on the delegate declaration. This error has nothing to do with the fact that your using a
delegate :) My sample code didn't specify it because it was intended for use within class-scope.

Try:

public delegate void callbackEvent() ;

--
Dave Sexton
dave@www..jwaon line..com
-----------------------------------------------------------------------
"Wayne Weeks" <WayneWeeks@dis cussions.micros oft.com> wrote in message news:D0A4B1FC-242F-482C-AEB6-21F437359172@mi crosoft.com...[color=blue]
> OK, thankyou, yes that makes sense, need to make the parameter types the
> same. Just one final issue and I hope I can move on with the fun part of
> this application. As you note, I added the declaration of the delegate to
> the library code as follows:
>
> public class ptAPI
> {
> delegate void callbackEvent() ;
>
> [DllImport("pats api.dll")]
> public static extern int ptRegisterLinkS tateCallback(in t callbackID,
> callbackEvent Callback);
> }
>
> However when I try to recompile the library the compiler complains that
> there is "Inconsiste nt accessibility", parameter type ptAPI.callbackE vent is
> less accessibile than ptAPI.ptRegiste rLinkStateCallb ack. Am I missing a
> switch for the compiler? Something wrong with declaration of the delegate in
> the library. This delegate construct is a tricky thing to grasp....thanks
> again, hopefully I can get past this soon.
>
> Wayne
>
>
>
> "Dave" wrote:
>[color=green]
>> No problem.
>>
>> The declaration for your interop call (external method) should also declare the paramter type as the delegate your passing it:
>>[color=darkred]
>> > [DllImport("pats api.dll")]
>> > public static extern int ptRegisterLinkS tateCallback(in t callbackID, callbackEvent CallBack);[/color]
>>
>> This, of course, means that you have to declare the delegate in your library and not the consuming program.
>>
>> --
>> Dave Sexton
>> dave@www..jwaon line..com
>> -----------------------------------------------------------------------
>> "Wayne Weeks" <WayneWeeks@dis cussions.micros oft.com> wrote in message news:A05B408C-E89D-4B96-B8CD-C9F4753158F5@mi crosoft.com...[color=darkred]
>> > Thanks Dave,
>> >
>> > I was confused on how to use delegates, but I think I understand how they
>> > are used now. I have used your code as the basis for correcting what I had
>> > done. I still have one final issue that perhaps you may know how to fix.
>> > Here is the code:
>> >
>> > delegate void callbackEvent() ;
>> >
>> > void MyCallback()
>> > {
>> > MessageBox.Show ("Callback Event Received");
>> > }
>> >
>> > private void ptRegisterLinkS tateCallback_Cl ick(object sender, EventArgs e)
>> > {
>> > callbackEvent cb = new callbackEvent(M yCallback);
>> > status = ptAPI.ptRegiste rLinkStateCallb ack(ptHostLinkS tateChange, cb);
>> > MessageBox.Show ("Status = " + status.ToString ());
>> > }
>> >
>> > So when the "ptRegisterLink ...." button is clicked a pointer, cb, is created
>> > to MyCallback. The "ptAPI.ptRegist er..." function call is to an external DLL
>> > using DLLImport and I am expecting the 'cb' argument to be the pointer to the
>> > MyCallback method. The code in the DLL is:
>> >
>> > public class ptAPI
>> > {
>> > [DllImport("pats api.dll")]
>> > public static extern int ptRegisterLinkS tateCallback(in t callbackID, int
>> > mtdAddress);
>> > }
>> >
>> > The compiler complains that there are invalid arguments and that argument 2
>> > 'cannot convert from "...Form1.callb ackEvent to int". Clearly I still have
>> > something wrong with my code.
>> >
>> > Any ideas as to why this is wrong? Thanks for your help with this, much
>> > appreciated.
>> >
>> > Wayne
>> >
>> > "Dave" wrote:
>> >
>> >> > callbackEvent Event = delegate()
>> >> > {
>> >> > MessageBox.Show ("Callback Event Received");
>> >> > }
>> >>
>> >> The above syntax is incorrect.
>> >> Treat your callback as a method:
>> >>
>> >> delegate void callbackEvent() ;
>> >>
>> >> void MyCallBack()
>> >> {
>> >> MessageBox.Show ("Callback Event Received");
>> >> }
>> >>
>> >> void ConsumeDelegate ()
>> >> {
>> >> // Create a pointer to MyCallBack using the callbackEvent signature:
>> >> callbackEvent cb = new callbackEvent(M yCallBack);
>> >>
>> >> // Use the method pointer in your interop call:
>> >> myAPIregister(c b);
>> >>
>> >> // > The parameter in myAPIregister(p arameter) is
>> >> // > expecting a pointer to the callback handler.
>> >> //
>> >> // .NET Interop will automattically Marshal the delegate you pass to the external method as a pointer to the method
>> >> }
>> >>
>> >> --
>> >> Dave Sexton
>> >> dave@www..jwaon line..com
>> >> -----------------------------------------------------------------------
>> >> "Wayne Weeks" <Wayne Weeks@discussio ns.microsoft.co m> wrote in message
>> >> news:35A6F85C-A4DF-4F05-AED1-AC9667C96F4F@mi crosoft.com...
>> >> >I am trying to use delegates for the first time and I am probably missing
>> >> > something. I have a legacy DLL and I have used DllImport to get to the
>> >> > functions that it contains...the normal function calls work fine, but I can't
>> >> > get callbacks to work. The delegate declaration etc is below.
>> >> >
>> >> > public delegate void callbackEvent() ;
>> >> >
>> >> > callbackEvent Event = delegate()
>> >> > {
>> >> > MessageBox.Show ("Callback Event Received");
>> >> > }
>> >> >
>> >> >
>> >> > The function in the DLL to register the callback is
>> >> >
>> >> > myAPIregister(E vent);
>> >> >
>> >> > So I am expecting that myAPIregister(E vent) will provide a pointer to the
>> >> > Event delegate. When the callback event occurs it should simply display the
>> >> > MessageBox with the text. The parameter in myAPIregister(p arameter) is
>> >> > expecting a pointer to the callback handler.
>> >> >
>> >> > I have done a lot of reading about delegates over the past few days to get
>> >> > this far but I appear to be missing something. The Compiler complains that
>> >> > the argument is invalid.
>> >> >
>> >> > Thanks for any help and guidance.
>> >>
>> >>
>> >>[/color]
>>
>>
>>[/color][/color]

**Wayne Weeks** · Nov 17 '05, 02:05 AM

Re: Delegates and pointers

Dave, a big thank you....finally I can get the code to build and it seems to
work....thanks again for your support getting this resolved...now on to more
interesting development.

"Dave" wrote:
[color=blue]
> you haven't specified an access modifier on the delegate declaration. This error has nothing to do with the fact that your using a
> delegate :) My sample code didn't specify it because it was intended for use within class-scope.
>
> Try:
>
> public delegate void callbackEvent() ;
>
>
>
> --
> Dave Sexton
> dave@www..jwaon line..com
> -----------------------------------------------------------------------
> "Wayne Weeks" <WayneWeeks@dis cussions.micros oft.com> wrote in message news:D0A4B1FC-242F-482C-AEB6-21F437359172@mi crosoft.com...[color=green]
> > OK, thankyou, yes that makes sense, need to make the parameter types the
> > same. Just one final issue and I hope I can move on with the fun part of
> > this application. As you note, I added the declaration of the delegate to
> > the library code as follows:
> >
> > public class ptAPI
> > {
> > delegate void callbackEvent() ;
> >
> > [DllImport("pats api.dll")]
> > public static extern int ptRegisterLinkS tateCallback(in t callbackID,
> > callbackEvent Callback);
> > }
> >
> > However when I try to recompile the library the compiler complains that
> > there is "Inconsiste nt accessibility", parameter type ptAPI.callbackE vent is
> > less accessibile than ptAPI.ptRegiste rLinkStateCallb ack. Am I missing a
> > switch for the compiler? Something wrong with declaration of the delegate in
> > the library. This delegate construct is a tricky thing to grasp....thanks
> > again, hopefully I can get past this soon.
> >
> > Wayne
> >
> >
> >
> > "Dave" wrote:
> >[color=darkred]
> >> No problem.
> >>
> >> The declaration for your interop call (external method) should also declare the paramter type as the delegate your passing it:
> >>
> >> > [DllImport("pats api.dll")]
> >> > public static extern int ptRegisterLinkS tateCallback(in t callbackID, callbackEvent CallBack);
> >>
> >> This, of course, means that you have to declare the delegate in your library and not the consuming program.
> >>
> >> --
> >> Dave Sexton
> >> dave@www..jwaon line..com
> >> -----------------------------------------------------------------------
> >> "Wayne Weeks" <WayneWeeks@dis cussions.micros oft.com> wrote in message news:A05B408C-E89D-4B96-B8CD-C9F4753158F5@mi crosoft.com...
> >> > Thanks Dave,
> >> >
> >> > I was confused on how to use delegates, but I think I understand how they
> >> > are used now. I have used your code as the basis for correcting what I had
> >> > done. I still have one final issue that perhaps you may know how to fix.
> >> > Here is the code:
> >> >
> >> > delegate void callbackEvent() ;
> >> >
> >> > void MyCallback()
> >> > {
> >> > MessageBox.Show ("Callback Event Received");
> >> > }
> >> >
> >> > private void ptRegisterLinkS tateCallback_Cl ick(object sender, EventArgs e)
> >> > {
> >> > callbackEvent cb = new callbackEvent(M yCallback);
> >> > status = ptAPI.ptRegiste rLinkStateCallb ack(ptHostLinkS tateChange, cb);
> >> > MessageBox.Show ("Status = " + status.ToString ());
> >> > }
> >> >
> >> > So when the "ptRegisterLink ...." button is clicked a pointer, cb, is created
> >> > to MyCallback. The "ptAPI.ptRegist er..." function call is to an external DLL
> >> > using DLLImport and I am expecting the 'cb' argument to be the pointer to the
> >> > MyCallback method. The code in the DLL is:
> >> >
> >> > public class ptAPI
> >> > {
> >> > [DllImport("pats api.dll")]
> >> > public static extern int ptRegisterLinkS tateCallback(in t callbackID, int
> >> > mtdAddress);
> >> > }
> >> >
> >> > The compiler complains that there are invalid arguments and that argument 2
> >> > 'cannot convert from "...Form1.callb ackEvent to int". Clearly I still have
> >> > something wrong with my code.
> >> >
> >> > Any ideas as to why this is wrong? Thanks for your help with this, much
> >> > appreciated.
> >> >
> >> > Wayne
> >> >
> >> > "Dave" wrote:
> >> >
> >> >> > callbackEvent Event = delegate()
> >> >> > {
> >> >> > MessageBox.Show ("Callback Event Received");
> >> >> > }
> >> >>
> >> >> The above syntax is incorrect.
> >> >> Treat your callback as a method:
> >> >>
> >> >> delegate void callbackEvent() ;
> >> >>
> >> >> void MyCallBack()
> >> >> {
> >> >> MessageBox.Show ("Callback Event Received");
> >> >> }
> >> >>
> >> >> void ConsumeDelegate ()
> >> >> {
> >> >> // Create a pointer to MyCallBack using the callbackEvent signature:
> >> >> callbackEvent cb = new callbackEvent(M yCallBack);
> >> >>
> >> >> // Use the method pointer in your interop call:
> >> >> myAPIregister(c b);
> >> >>
> >> >> // > The parameter in myAPIregister(p arameter) is
> >> >> // > expecting a pointer to the callback handler.
> >> >> //
> >> >> // .NET Interop will automattically Marshal the delegate you pass to the external method as a pointer to the method
> >> >> }
> >> >>
> >> >> --
> >> >> Dave Sexton
> >> >> dave@www..jwaon line..com
> >> >> -----------------------------------------------------------------------
> >> >> "Wayne Weeks" <Wayne Weeks@discussio ns.microsoft.co m> wrote in message
> >> >> news:35A6F85C-A4DF-4F05-AED1-AC9667C96F4F@mi crosoft.com...
> >> >> >I am trying to use delegates for the first time and I am probably missing
> >> >> > something. I have a legacy DLL and I have used DllImport to get to the
> >> >> > functions that it contains...the normal function calls work fine, but I can't
> >> >> > get callbacks to work. The delegate declaration etc is below.
> >> >> >
> >> >> > public delegate void callbackEvent() ;
> >> >> >
> >> >> > callbackEvent Event = delegate()
> >> >> > {
> >> >> > MessageBox.Show ("Callback Event Received");
> >> >> > }
> >> >> >
> >> >> >
> >> >> > The function in the DLL to register the callback is
> >> >> >
> >> >> > myAPIregister(E vent);
> >> >> >
> >> >> > So I am expecting that myAPIregister(E vent) will provide a pointer to the
> >> >> > Event delegate. When the callback event occurs it should simply display the
> >> >> > MessageBox with the text. The parameter in myAPIregister(p arameter) is
> >> >> > expecting a pointer to the callback handler.
> >> >> >
> >> >> > I have done a lot of reading about delegates over the past few days to get
> >> >> > this far but I appear to be missing something. The Compiler complains that
> >> >> > the argument is invalid.
> >> >> >
> >> >> > Thanks for any help and guidance.
> >> >>
> >> >>
> >> >>
> >>
> >>
> >>[/color][/color]
>
>
>[/color]

Delegates and pointers

Delegates and pointers

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