Accessing a DLL from C#

[Alfred B. Thordarson]

I have a problem accessing a DLL using C#.

I'm using C/FRONT with Navision's CFRONT.DLL, which contains the
method:

DBL_S32* DBL_NextKey(DBL _HTABLE hTable, DBL_S32* Key);
typedef signed long int DBL_S32;

In addition the documentation says that "hTable" is the "Handle to the
table" and "Key" is "A table key or a NULL". Trying to access this
method from C# (FYI: I'm using Visual Studio), I see the method
defined as:

object CFRONTClass.Nex tKey(int hTable,ref object key);

The first parameter is not a problem. I have a valid integer for the
hTable, which works for other methods that don't take "object" as a
parameter. But I would like to send "NULL" (as the documentation
describes) as the second parameter (key), it is this paramter's actual
type that is my problem.

I have spent some time on figuring out what the type should be but I
get type mismatch exceptions for all the different types like int[],
Int32[], object[], etc. In the end I found the IntPtr type and now I'm
writing the code as:

IntPtr[] key=new IntPtr[21];
object keyObject=(obje ct)key;
nav.NextKey(hTa bleRef,ref keyObject);

This gets me further but doesn't work. Besides, it is not NULL, it is
just a reference to an array of integer pointers (as I understand it).
This code now gives me the following exception:

An unhandled exception of type
'System.Runtime .InteropService s.COMException' occurred in mscorlib.dll
Additional information: Old format or invalid type library.
Unhandled Exception: System.Runtime. InteropServices .COMException
(0x80028019): Old format or invalid type library.
at System.RuntimeT ype.InvokeDispM ethod(String name, BindingFlags
invokeAttr, Object target, Object[] args, Boolean[]
byrefModifiers, Int32 culture, String[] namedParameters )
at System.RuntimeT ype.InvokeMembe r(String name, BindingFlags
invokeAttr, Binder binder, Object target, Object[] args,
ParameterModifi er[] modifiers, CultureInfo culture, String[]
namedParameters )
at System.RuntimeT ype.ForwardCall ToInvokeMember( String memberName,
BindingFlags flags, Object target, Int32[] aWrapperTypes,
MessageData& msgData)
at CFRONTLib.CFRON TClass.NextKey( Int32 hTable, Object& Key)
at WinNavAccessApp .Form1..ctor() in
c:\alfred\vstud io\wstest\winna vaccessapp\form 1.cs:line 90
at WinNavAccessApp .Form1.Main() in
c:\alfred\vstud io\wstest\winna vaccessapp\form 1.cs:line 148
The program '[1692] WinNavAccessApp .exe' has exited with code 0 (0x0).

I'm totally stuck here and need some help with changing my code above
so that I send the proper type and value into the NextKey method

I would appreciate all the help you could give me.

[Greg Ewing [MVP]]

Alfred, have you tried just passing null like this? I've never used that
dll myself but sounds like that might work for you.

IntPtr[] key=new IntPtr[21];
nav.NextKey(hTa bleRef, null);

--
Greg Ewing [MVP]
http://www.citidc.com/


"Alfred B. Thordarson" <at*********@la ndsteinar.je> wrote in message
news:79******** *************** ***@posting.goo gle.com...

I have a problem accessing a DLL using C#.

I'm using C/FRONT with Navision's CFRONT.DLL, which contains the
method:

DBL_S32* DBL_NextKey(DBL _HTABLE hTable, DBL_S32* Key);
typedef signed long int DBL_S32;

In addition the documentation says that "hTable" is the "Handle to the
table" and "Key" is "A table key or a NULL". Trying to access this
method from C# (FYI: I'm using Visual Studio), I see the method
defined as:

object CFRONTClass.Nex tKey(int hTable,ref object key);

The first parameter is not a problem. I have a valid integer for the
hTable, which works for other methods that don't take "object" as a
parameter. But I would like to send "NULL" (as the documentation
describes) as the second parameter (key), it is this paramter's actual
type that is my problem.

I have spent some time on figuring out what the type should be but I
get type mismatch exceptions for all the different types like int[],
Int32[], object[], etc. In the end I found the IntPtr type and now I'm
writing the code as:

IntPtr[] key=new IntPtr[21];
object keyObject=(obje ct)key;
nav.NextKey(hTa bleRef,ref keyObject);

This gets me further but doesn't work. Besides, it is not NULL, it is
just a reference to an array of integer pointers (as I understand it).
This code now gives me the following exception:

An unhandled exception of type
'System.Runtime .InteropService s.COMException' occurred in mscorlib.dll
Additional information: Old format or invalid type library.
Unhandled Exception: System.Runtime. InteropServices .COMException
(0x80028019): Old format or invalid type library.
at System.RuntimeT ype.InvokeDispM ethod(String name, BindingFlags
invokeAttr, Object target, Object[] args, Boolean[]
byrefModifiers, Int32 culture, String[] namedParameters )
at System.RuntimeT ype.InvokeMembe r(String name, BindingFlags
invokeAttr, Binder binder, Object target, Object[] args,
ParameterModifi er[] modifiers, CultureInfo culture, String[]
namedParameters )
at System.RuntimeT ype.ForwardCall ToInvokeMember( String memberName,
BindingFlags flags, Object target, Int32[] aWrapperTypes,
MessageData& msgData)
at CFRONTLib.CFRON TClass.NextKey( Int32 hTable, Object& Key)
at WinNavAccessApp .Form1..ctor() in
c:\alfred\vstud io\wstest\winna vaccessapp\form 1.cs:line 90
at WinNavAccessApp .Form1.Main() in
c:\alfred\vstud io\wstest\winna vaccessapp\form 1.cs:line 148
The program '[1692] WinNavAccessApp .exe' has exited with code 0 (0x0).

I'm totally stuck here and need some help with changing my code above
so that I send the proper type and value into the NextKey method

I would appreciate all the help you could give me.

[Alfred B. Thordarson]

No I haven't; because you can't pass a null to a ref parameter. A ref
parameter requires the caller to pass a valid object of the proper
type. My question is what is a proper C# type to a "ref object" that
is being marshalled to the type (signed long int *) in a dll written
in C.

"Greg Ewing [MVP]" <gewing@_NO_SPA M_citidc.com> wrote in message news:<e0******* ******@TK2MSFTN GP10.phx.gbl>.. .

Alfred, have you tried just passing null like this? I've never used that
dll myself but sounds like that might work for you.

IntPtr[] key=new IntPtr[21];
nav.NextKey(hTa bleRef, null);

--
Greg Ewing [MVP]
http://www.citidc.com/

[Alfred B. Thordarson]

I also tried to add a reference to the CFRONT.DLL in a managed C++
ClassLibrary Project and then I get the following declaration:

object __gc *NextKey(int, object __gc * __gc *)

If I now use this method as:

Object __gc *key=Navision->NextKey(TableH andle,NULL);

I get An unhandled exception of type 'System.Executi onEngineExcepti on'
occurred in mscorlib.dll. Probably because the DLL doesn't like the
NULL. So, I tried the following code:

Object __gc * __gc *keyPtr;
(*keyPtr)=NULL;
Object __gc *key=Navision->NextKey(TableH andle,keyPtr);

Again I get an exception:

Unhandled Exception: System.NullRefe renceException: Object reference
not set to an instance of an object.
at CPPNavLib.Class 1.GetKey(Int32 TableHandle, Int32 KeyNo) in
c:\alfred\vstud io\wstest\cppna vlib\cppnavlib. cpp:line 47
at WinNavAccessApp .Form1..ctor() in
c:\alfred\vstud io\wstest\winna vaccessapp\form 1.cs:line 91
at WinNavAccessApp .Form1.Main() in
c:\alfred\vstud io\wstest\winna vaccessapp\form 1.cs:line 152
The program '[2928] WinNavAccessApp .exe' has exited with code 0 (0x0).

Isn't there someone out there that can help me?

[Greg Ewing [MVP]]

Alfred, how about this:

Object o = null;
nav.NextKey(hTa bleRef, ref o);

--
Greg Ewing [MVP]
http://www.citidc.com/


"Alfred B. Thordarson" <at*********@la ndsteinar.je> wrote in message
news:79******** *************** ***@posting.goo gle.com...

No I haven't; because you can't pass a null to a ref parameter. A ref
parameter requires the caller to pass a valid object of the proper
type. My question is what is a proper C# type to a "ref object" that
is being marshalled to the type (signed long int *) in a dll written
in C.

"Greg Ewing [MVP]" <gewing@_NO_SPA M_citidc.com> wrote in message

news:<e0******* ******@TK2MSFTN GP10.phx.gbl>.. .

Alfred, have you tried just passing null like this? I've never used that dll myself but sounds like that might work for you.

IntPtr[] key=new IntPtr[21];
nav.NextKey(hTa bleRef, null);

--
Greg Ewing [MVP]
http://www.citidc.com/

[Alfred B. Thordarson]

Hi Greg.

You wrote:

Object o = null;
nav.NextKey(hTa bleRef, ref o);
Unfortunatelly you can not send in a ref to null - it compiles but
gives a runtime exception:

An unhandled exception of type 'System.NullRef erenceException '
occurred in mscorlib.dll
Additional information: Object reference
not set to an instance of an object.

-Alfred

"Greg Ewing [MVP]" <gewing@_NO_SPA M_citidc.com> wrote in message news:<eb******* *******@TK2MSFT NGP11.phx.gbl>. .. Alfred, how about this:

Object o = null;
nav.NextKey(hTa bleRef, ref o);

--
Greg Ewing [MVP]
http://www.citidc.com/


"Alfred B. Thordarson" <at*********@la ndsteinar.je> wrote in message
news:79******** *************** ***@posting.goo gle.com...

No I haven't; because you can't pass a null to a ref parameter. A ref
parameter requires the caller to pass a valid object of the proper
type. My question is what is a proper C# type to a "ref object" that
is being marshalled to the type (signed long int *) in a dll written
in C.

"Greg Ewing [MVP]" <gewing@_NO_SPA M_citidc.com> wrote in message

news:<e0******* ******@TK2MSFTN GP10.phx.gbl>.. .

Alfred, have you tried just passing null like this? I've never used that dll myself but sounds like that might work for you.

IntPtr[] key=new IntPtr[21];
nav.NextKey(hTa bleRef, null);

--
Greg Ewing [MVP]
http://www.citidc.com/

[Greg Ewing [MVP]]

Alfred, you can definitely send a null object as a ref. That error sounds
like the NextKey function isn't checking to make sure the object isn't null
before accessing it. Are you sure you are supposed to pass null as the
second parm?

Here's some code from a simple windows form which demonstrates that this is
possible.

private void Form1_Load(obje ct sender, System.EventArg s e)
{
object o = null;
Test(ref o);
}
private void Test(ref object o)
{
if (o == null)
MessageBox.Show ("o was null");
else
MessageBox.Show ("o was not null");
}

--
Greg Ewing [MVP]
http://www.citidc.com/

"Alfred B. Thordarson" <at*********@la ndsteinar.je> wrote in message
news:79******** *************** **@posting.goog le.com...

Hi Greg.

You wrote:

Object o = null;
nav.NextKey(hTa bleRef, ref o);

Unfortunatelly you can not send in a ref to null - it compiles but
gives a runtime exception:

An unhandled exception of type 'System.NullRef erenceException '
occurred in mscorlib.dll
Additional information: Object reference
not set to an instance of an object.

-Alfred

"Greg Ewing [MVP]" <gewing@_NO_SPA M_citidc.com> wrote in message

news:<eb******* *******@TK2MSFT NGP11.phx.gbl>. ..

Alfred, how about this:

Object o = null;
nav.NextKey(hTa bleRef, ref o);

--
Greg Ewing [MVP]
http://www.citidc.com/


"Alfred B. Thordarson" <at*********@la ndsteinar.je> wrote in message
news:79******** *************** ***@posting.goo gle.com...

No I haven't; because you can't pass a null to a ref parameter. A ref
parameter requires the caller to pass a valid object of the proper
type. My question is what is a proper C# type to a "ref object" that
is being marshalled to the type (signed long int *) in a dll written
in C.

"Greg Ewing [MVP]" <gewing@_NO_SPA M_citidc.com> wrote in message

news:<e0******* ******@TK2MSFTN GP10.phx.gbl>.. .

> Alfred, have you tried just passing null like this? I've never used

that

> dll myself but sounds like that might work for you.
>
> IntPtr[] key=new IntPtr[21];
> nav.NextKey(hTa bleRef, null);
>
> --
> Greg Ewing [MVP]
> http://www.citidc.com/