how to write a callback function to be invoked by C++ DLL?

[Wen]

hello,
now, i wanna port a c++ program into C# project. a DLL written by C++ and
keep it no change, and UI wirtten by C#.

my C++ UI code is as below:

// error handlers --global function callback function
// C++ dll would invoke this function if needed
void ImageConv_Callb ack_Handler(con st char *szInfo)
{
AfxMessageBox(s zInfo);
}

CXXXDlg::OnInit Dialog(...)
{
....
// Set Callback Function
SetImageConvCal lbackFunc(Image Conv_Callback_H andler);
....
}

{ // work flow
.....
}

and it works fine.

i wrote C# code for the same function, so that i need 2 write a callback
function in C#. my C# code is as below:

namespace ImageConvTest
{

partial class Form1 : Form
{
.....
public delegate void delegateCH(stri ng szInfo);

private void ImageConv_Callb ack_Handler(str ing szInfo)
{
MessageBox.Show (szInfo);
}

// error functions
[DllImport("Imag eConv.dll", EntryPoint = "SetImageConvCa llbackFunc")]
public static extern void
SetImageConvCal lbackFunc(deleg ateCHpFuncCallb ackProc);// in this case, is
delegateCHcorre ct? is it equal to "void *"???

private void Form1_Load(obje ct sender, EventArgs e)
{
InitImageConvLi brary();
//
delegateCH delegate_Callba ck_Handler = new
delegateCH(Imag eConv_Callback_ Handler);
SetImageConvCal lbackFunc(deleg ate_Callback_Ha ndler);
}

here, strange things happened to the C# project.
compiled it and got no errors. run it with no errors too. once i trigger the
function which is in C++ DLL, runtime exception occurs :-(

and if comments //SetImageConvCal lbackFunc(deleg ate_Callback_Ha ndler);
the program works fine.


is there any method to solve this problem? thank u very much.

--
With my kind regards,
Wen

[Roland Polzer]

RE: how to write a callback function to be invoked by C++ DLL?

Hi Wen,

Greetings form GarbageCollecti on!!!

you got in trouble cause of you lost the instance of your delegate (it's
only in your Form_Load).
[color=blue]
> public delegate void delegateCH(stri ng szInfo);[/color]

It's not an instance member, but a type declaration somewhat like this (the
compiler internally generates a type!!!)

public class delegateCH : Delegate{...}


So introduce in your Form a member of the delegate

partial class Form1 : Form
{

pivate static delegateCH _delegate_Callb ack_Handler = null;

[color=blue]
> private void Form1_Load(obje ct sender, EventArgs e)
> {[/color]
....

_delegate_Callb ack_Handler = new delegateCH(Imag eConv_Callback_ Handler);

SetImageConvCal lbackFunc(_dele gate_Callback_H andler);

....
}

I think it should work

Roland

[Wen]

Re: how to write a callback function to be invoked by C++ DLL?

[color=blue]
> Hi Wen,
>
> Greetings form GarbageCollecti on!!!
>
> you got in trouble cause of you lost the instance of your delegate (it's
> only in your Form_Load).
>[color=green]
> > public delegate void delegateCH(stri ng szInfo);[/color]
>
> It's not an instance member, but a type declaration somewhat like this[/color]
(the[color=blue]
> compiler internally generates a type!!!)
>
> public class delegateCH : Delegate{...}
>
>
> So introduce in your Form a member of the delegate
>
> partial class Form1 : Form
> {
>
> pivate static delegateCH _delegate_Callb ack_Handler = null;
>
>[color=green]
> > private void Form1_Load(obje ct sender, EventArgs e)
> > {[/color]
> ...
>
> _delegate_Callb ack_Handler = new delegateCH(Imag eConv_Callback_ Handler);
>
> SetImageConvCal lbackFunc(_dele gate_Callback_H andler);
>
> ...
> }
>
> I think it should work
>
> Roland[/color]

yes, i did and it works now, but when i trigger the function which is
implemented in C++ dll, the app will disappear :-(

these are APIs of my C++ DLL:
// Init & DeInit functions
IMAGECONV_API
void DLL_CALLCONV InitImageConvLi brary();
IMAGECONV_API
void DLL_CALLCONV DeInitImageConv Library();

// error functions
typedef void (*IMAGECONV_CAL LBACK)(const char *);
IMAGECONV_API

//void DLL_CALLCONV SetImageConvCal lbackFunc(void *pFuncCallbackP roc);
void DLL_CALLCONV SetImageConvCal lbackFunc(IMAGE CONV_CALLBACK
pFuncCallbackPr oc);

// do convert images functions

IMAGECONV_API
bool DLL_CALLCONV BMPtoGIF(int phoneType, const char *in_filename, const
char *out_filename);
IMAGECONV_API
bool DLL_CALLCONV BMPtoPNG(int phoneType, const char *in_filename, const
char *out_filename);

.....


in C# project, the related code is as following:
partial class Form1 : Form
{
... ...
public delegate void delegateCH(stri ng szInfo);

public void ImageConv_Callb ack_Handler(str ing szInfo)
{
MessageBox.Show (szInfo);
}

private static delegateCH _delegate_Callb ack_Handler = null;

// Init & Deinit
[DllImport("Imag eConv.dll", EntryPoint = "InitImageConvL ibrary")]
public static extern void InitImageConvLi brary();

[DllImport("Imag eConv.dll", EntryPoint = "DeInitImageCon vLibrary")]
public static extern void DeInitImageConv Library();

// error functions
[DllImport("Imag eConv.dll", EntryPoint =
"SetImageConvCa llbackFunc")]
public static extern void SetImageConvCal lbackFunc(deleg ateCH
pFuncCallbackPr oc);

// do convert images functions
[DllImport("Imag eConv.dll", EntryPoint = "BMPtoGIF")]
public static extern bool BMPtoGIF(int phoneType, string
in_filename, string out_filename);

[DllImport("Imag eConv.dll", EntryPoint = "BMPtoPNG")]
public static extern bool BMPtoPNG(int phoneType, string
in_filename, string out_filename);

.... ....

private void Form1_Load(obje ct sender, EventArgs e)
{
InitImageConvLi brary();
//
_delegate_Callb ack_Handler = new
delegateCH(Imag eConv_Callback_ Handler);
SetImageConvCal lbackFunc(_dele gate_Callback_H andler); // i must
comment this sentence to make the app run properly, and i cannot use
callback function to support more details for users :-(
}

private void Form1_FormClose d(object sender, FormClosedEvent Args e)
{
DeInitImageConv Library();
}

private void ImageConvert_Cl ick(object sender, EventArgs e)
{
....
if (strFileExtensi on.CompareTo(". BMP") == 0)
{
BMPtoPNG(m_nPho neTypeConversat ion, strSrcPath,
strDestPath);
}
else if (strFileExtensi on.CompareTo(". JPG") == 0)
{
JPEGtoPNG(m_nPh oneTypeConversa tion, strSrcPath,
strDestPath);
}
...
}


}
}


very strange! :-(

[Willy Denoyette [MVP]]

Re: how to write a callback function to be invoked by C++ DLL?


"Wen" <wenming_hu2002 @hotmail.com> wrote in message
news:eCcm82xCFH A.2180@TK2MSFTN GP12.phx.gbl...[color=blue]
>[color=green]
>> Hi Wen,
>>
>> Greetings form GarbageCollecti on!!!
>>
>> you got in trouble cause of you lost the instance of your delegate (it's
>> only in your Form_Load).
>>[color=darkred]
>> > public delegate void delegateCH(stri ng szInfo);[/color]
>>
>> It's not an instance member, but a type declaration somewhat like this[/color]
> (the[color=green]
>> compiler internally generates a type!!!)
>>
>> public class delegateCH : Delegate{...}
>>
>>
>> So introduce in your Form a member of the delegate
>>
>> partial class Form1 : Form
>> {
>>
>> pivate static delegateCH _delegate_Callb ack_Handler = null;
>>
>>[color=darkred]
>> > private void Form1_Load(obje ct sender, EventArgs e)
>> > {[/color]
>> ...
>>
>> _delegate_Callb ack_Handler = new delegateCH(Imag eConv_Callback_ Handler);
>>
>> SetImageConvCal lbackFunc(_dele gate_Callback_H andler);
>>
>> ...
>> }
>>
>> I think it should work
>>
>> Roland[/color]
>
> yes, i did and it works now, but when i trigger the function which is
> implemented in C++ dll, the app will disappear :-(
>
> these are APIs of my C++ DLL:
> // Init & DeInit functions
> IMAGECONV_API
> void DLL_CALLCONV InitImageConvLi brary();
> IMAGECONV_API
> void DLL_CALLCONV DeInitImageConv Library();
>
> // error functions
> typedef void (*IMAGECONV_CAL LBACK)(const char *);
> IMAGECONV_API
>[/color]

How is IMAGECONV_CALLB ACK defined (typedef)?

Willy.