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.ExecuteSQLTask2
Set oTask = goPackage.Tasks.New("DTSExecuteSQLTask")
Set oCustomTask0 = oTask.CustomTask


......doesn't work in my C# app. Here's how I've ported it:

DTS.Task oTask;
DTS.ExecuteSQLTask2 oCustomTask0;
oTask = goPackage.Tasks.New("DTSExecuteSQLTask");
oCustomTask0 = (DTS.ExecuteSQLTask2) oTask.CustomTask; //<----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]

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.ExecuteSQLTask2
Set oTask = goPackage.Tasks.New("DTSExecuteSQLTask")
Set oCustomTask0 = oTask.CustomTask


.....doesn't work in my C# app. Here's how I've ported it:

DTS.Task oTask;
DTS.ExecuteSQLTask2 oCustomTask0;
oTask = goPackage.Tasks.New("DTSExecuteSQLTask");
oCustomTask0 = (DTS.ExecuteSQLTask2) oTask.CustomTask; //<----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.ExecuteSQLTask2)oTask.CustomTask;], 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.SqlServer.DTSPkg80.CustomTask' to
'Microsoft.SqlServer.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/default.asp?url=/library/en-us/dtsprog/dtspothobj_9nhw.asp

 

[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.CustomTask is and try
explicitly casting to that. I'd imagine it will be an interface instead.

GL

 

[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