Hi , I have some problem to access the twain interface using a callback function.

Here is the c-code for the function (Plattform is MS-Windows):

#ifdef _MSWIN_

TW_UINT16 FAR PASCAL DSM_Entry( pTW_IDENTITY pOrigin,

pTW_IDENTITY pDest,

TW_UINT32 DG,

TW_UINT16 DAT,

TW_UINT16 MSG,

TW_MEMREF pData);

and my JNA interface:

public interface Twain extends Library {

public static interface DSM_Entry extends Callback {

public int callback(TW_IDENTITY origin, //source of message

TW_IDENTITY dest, //destination of message

int dg, //data group ID: DG_xxxx

short dat, //data argument type: DAT_xxxx

short msg, //message ID: MSG_xxxx

Structure data); //pointer to data (TW_MEMREF = LPVOID)

}//end class DSM_Entry

}//end interface Twain

The C-structure of the pTW_IDENTITY from twain.h:

/* DAT_IDENTITY. Identifies the program/library/code resource. */

typedef struct {

TW_UINT32 Id; /* Unique number. In Windows, application hWnd */

TW_VERSION Version; /* Identifies the piece of code */

TW_UINT16 ProtocolMajor; /* Application and DS must set to TWON_PROTOCOLMAJOR */

TW_UINT16 ProtocolMinor; /* Application and DS must set to TWON_PROTOCOLMINOR */

TW_UINT32 SupportedGroups; /* Bit field OR combination of DG_ constants */

TW_STR32 Manufacturer; /* Manufacturer name, e.g. "Hewlett- Packard" */

TW_STR32 ProductFamily; /* Product family name, e.g. "ScanJet" */

TW_STR32 ProductName; /* Product name, e.g. "ScanJet Plus" */

} TW_IDENTITY, FAR * pTW_IDENTITY;

The java code I tried:

public class TW_IDENTITY extends Structure {

public int Id; // hWnd

public TW_VERSION Version; // TW_VERSION

public short ProtocolMajor; // TW_UINT16

public short ProtocolMinor; // TW_UINT16

public int SupportedGroups; // TW_UINT32

public String Manufacturer; // TW_STR32

public String Productfamily;

public String ProductName;

}//end class

The pData should be a pointer to the user interface:

C:

/* DAT_USERINTERFACE. Coordinates UI between application and data source. */

typedef struct {

TW_BOOL ShowUI; /* TRUE if DS should bring up its UI */

TW_BOOL ModalUI; /* For Mac only - true if the DS's UI is modal */

TW_HANDLE hParent; /* For windows only - Application window handle */

} TW_USERINTERFACE, FAR * pTW_USERINTERFACE;

Java:

public class TW_USERINTERFACE extends Structure {

public boolean ShowUI;

public boolean ModalUI;

public Pointer hParent;

} //end class TW_Userinterface

I tried this interface but got an Exception in thread "main" java.lang.NullPointerException

For the sake of completeness the source of the main program:

import com.sun.jna.*;

import image.twain.*;

public class JCam {

public interface Twain extends Library {

public static interface DSM_Entry extends Callback {

public int callback(TW_IDENTITY origin, //source of message

TW_IDENTITY dest, //destination of message

int dg, //data group ID: DG_xxxx

short dat, //data argument type: DAT_xxxx

short msg, //message ID: MSG_xxxx

Structure data); //pointer to data (TW_MEMREF = LPVOID)

}//end class DSM_Entry

}//end interface Twain

public static Twain.DSM_Entry dsm_entry;

public static TW_IDENTITY origin = new TW_IDENTITY();

public static TW_USERINTERFACE ui = new TW_USERINTERFACE();

public static void main(String[] args) {

//

Twain twain = (Twain) Native.loadLibrary("twain_32", Twain.class);

//Definition of Origin

origin.Id = 0; //null;

origin.Version.MajorNum = 0;

origin.Version.MinorNum = 1;

origin.Version.Language = TWAIN.TWLG_GER;

origin.Version.Country = TWAIN.TWCY_GERMANY;

origin.Version.Info = "JCam 0.1";

origin.ProtocolMajor = TWAIN.TWON_PROTOCOLMAJOR;

origin.ProtocolMinor = TWAIN.TWON_PROTOCOLMINOR;

origin.SupportedGroups = TWAIN.DG_CONTROL | TWAIN.DG_IMAGE;

origin.Manufacturer = "Hans-Guenter Krull";

origin.Productfamily = "Java based image capture";

origin.ProductName = "JCam";

int test = dsm_entry.callback(origin,

(TW_IDENTITY) null,

TWAIN.DG_CONTROL,

TWAIN.DAT_USERINTERFACE,

TWAIN.MSG_ENABLEDS,

ui);

}

} //end of class

Sorry for the stupid question