c# interop question-- QueryInterface trouble

[Jim Bancroft]

Hi everyone,

I've recently ported a COM component into .Net using a runtime callable
wrapper. The component in question is SQL Server's DTS package, if that
helps.

The import worked well enough....now I'm having some trouble using the
component. Specifically, this code below from VB6, which works:

Dim oTask As DTS.Task
Dim oCustomTask0 As DTS.ExecuteSQLT ask2
Set oTask = goPackage.Tasks .New("DTSExecut eSQLTask")
Set oCustomTask0 = oTask.CustomTas k
......doesn't work in my C# app. Here's how I've ported it:

DTS.Task oTask;
DTS.ExecuteSQLT ask2 oCustomTask0;
oTask = goPackage.Tasks .New("DTSExecut eSQLTask");
oCustomTask0 = (DTS.ExecuteSQL Task2) oTask.CustomTas k; //<----blows up here

On the last line above, where I do a cast, I get a runtime error telling me
QueryInterface failed. I'm not sure why it would fail in C#, when the
equivalent code in VB6 worked. Would anyone have an idea what I've done
wrong? Thanks!

[Jianwei Sun]

Jim Bancroft wrote:

Hi everyone,

I've recently ported a COM component into .Net using a runtime callable
wrapper. The component in question is SQL Server's DTS package, if that
helps.

The import worked well enough....now I'm having some trouble using the
component. Specifically, this code below from VB6, which works:

Dim oTask As DTS.Task
Dim oCustomTask0 As DTS.ExecuteSQLT ask2
Set oTask = goPackage.Tasks .New("DTSExecut eSQLTask")
Set oCustomTask0 = oTask.CustomTas k
.....doesn't work in my C# app. Here's how I've ported it:

DTS.Task oTask;
DTS.ExecuteSQLT ask2 oCustomTask0;
oTask = goPackage.Tasks .New("DTSExecut eSQLTask");
oCustomTask0 = (DTS.ExecuteSQL Task2) oTask.CustomTas k; //<----blows up here

On the last line above, where I do a cast, I get a runtime error telling me
QueryInterface failed. I'm not sure why it would fail in C#, when the
equivalent code in VB6 worked. Would anyone have an idea what I've done
wrong? Thanks!

Why do you need cast in [ oCustomTask0 =
(DTS.ExecuteSQL Task2)oTask.Cus tomTask;], based on your VB code, I don't
see you need a cast here. Is "CustomTask " defined in the default
interface DTS.Tas implement?

[Jim Bancroft]

Hi,

I'm doing the cast because if I don't, I get this error when compiling:

Cannot implicitly convert type 'Microsoft.SqlS erver.DTSPkg80. CustomTask' to
'Microsoft.SqlS erver.DTSPkg80. ExecuteSQLTask2

So, I figured a cast was the way to go. CustomTask inherits from DTS.Task,
if that helps.

Here's the hierarchy, if you're interested:
http://msdn.microsoft.com/library/de...thobj_9nhw.asp

Why do you need cast in [ oCustomTask0 =
(DTS.ExecuteSQL Task2)oTask.Cus tomTask;], based on your VB code, I don't
see you need a cast here. Is "CustomTask " defined in the default interface
DTS.Tas implement?

[Dave]

The fact that it's not a casting exception leads me to believe that your not doing anything wrong (unless you modified the type
library before importing) and that the wrapper is at fault.

Another possibility:

Your casting to a class it seems, and not an interface. In my experience I've found that marshalled members, in some cases, must be
cast to an interface and not a class. Try breaking on that line in a debugger and see what Type oTask.CustomTas k is and try
explicitly casting to that. I'd imagine it will be an interface instead.

GL

--
Dave Sexton
dave@www..jwaon line..com
-----------------------------------------------------------------------
"Jim Bancroft" <as******@nowhe re.com> wrote in message news:Ol******** ******@TK2MSFTN GP10.phx.gbl...

Hi everyone,

I've recently ported a COM component into .Net using a runtime callable wrapper. The component in question is SQL Server's DTS
package, if that helps.

The import worked well enough....now I'm having some trouble using the component. Specifically, this code below from VB6, which
works:

Dim oTask As DTS.Task
Dim oCustomTask0 As DTS.ExecuteSQLT ask2
Set oTask = goPackage.Tasks .New("DTSExecut eSQLTask")
Set oCustomTask0 = oTask.CustomTas k
.....doesn't work in my C# app. Here's how I've ported it:

DTS.Task oTask;
DTS.ExecuteSQLT ask2 oCustomTask0;
oTask = goPackage.Tasks .New("DTSExecut eSQLTask");
oCustomTask0 = (DTS.ExecuteSQL Task2) oTask.CustomTas k; //<----blows up here

On the last line above, where I do a cast, I get a runtime error telling me QueryInterface failed. I'm not sure why it would fail
in C#, when the equivalent code in VB6 worked. Would anyone have an idea what I've done wrong? Thanks!

[Jim Bancroft]

Thanks for the help. I think I've found out what's wrong. It seems there's
a problem with DTS in versions of SQL Server 2000 without Service Pack 2
installed:

http://www.sqldts.com/default.aspx?6,222,286,0,1
I'm off to update my installation now. Hope that fixes things!

Thanks everyone!

-Jim
"Dave" <NO*********@do tcomdatasolutio ns.com> wrote in message
news:ux******** ******@TK2MSFTN GP09.phx.gbl...

The fact that it's not a casting exception leads me to believe that your
not doing anything wrong (unless you modified the type library before
importing) and that the wrapper is at fault.

Another possibility:

Your casting to a class it seems, and not an interface. In my experience
I've found that marshalled members, in some cases, must be cast to an
interface and not a class. Try breaking on that line in a debugger and
see what Type oTask.CustomTas k is and try explicitly casting to that. I'd
imagine it will be an interface instead.

GL