How to mimick VB use of COM Object Interface using C#

Question

I am working with a vendor's API. It is supplied as various COM object DLL's. I am trying to gain access to method "CreateDisconnectedADORecordset" contained within the interface IBBUtilityCode.

A code sample from the vendor is as follows:

Dim oReservices As New REServices
Dim oUtilCode As IBBUtilityCode
Dim rs As Recordset
Dim sSQL As String

sSQL = "SELECT * FROM CONSTITUENT_BANK"

oReservices.Init SessionContext
Set oUtilCode = oReservices

Set rs = oUtilCode.CreateDisconnectedADORecordset(sSQL)

They seem to be using the interface "IBBUtilityCode" by first declaring a pointer to one, then casting "oReservices" as a pointer to the interface???

I am not a VB programmer, so I really haven't a clue.

How can this be done with C#? Any help and/or pointers you can give me would be greatly appreciated.

Thanks, Jimmy

Hans Passant · Accepted Answer · 2014-03-15 17:17:57Z

1

They seem to be using the interface "IBBUtilityCode" by first declaring a pointer to one, then casting "oReservices" as a pointer to the interface???

The concept of a class implementing an interface is not special to COM or Visual Basic, you should be familiar with it in C# as well. Just as in this VB6 code, you don't need a cast to obtain the interface reference. The translation is entirely mechanical:

var oReservices = new REServices();
oReservices.Init(SessionContext);
IBBUtilityCode oUtilCode = oReservices
var sSQL = "SELECT * FROM CONSTITUENT_BANK"
var rs = oUtilCode.CreateDisconnectedADORecordset(sSQL)

No lack of traps with this kind of component, ADO has not aged well. A minor install or configuration problem can turn into a pretty unsolvable headache. Be sure to contact the vendor or author of this component when you have trouble.

answered Mar 15, 2014 at 17:17

Hans Passant

946k151 gold badges1.8k silver badges2.6k bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

JConnell Over a year ago

Hans: Your solution is correct and I had tried something like that earlier. What I discovered that prevented me from using it was that I needed to set "Embed Interop Types" in the properties of the DLL to "false". Once I made that change, everything began to work. Thanks for your help.

attila · Accepted Answer · 2014-03-15 17:00:09Z

0

I would suggest using cominvoke. Here is a link from Microsoft explaining it: http://msdn.microsoft.com/en-us/library/aa645736(v=vs.71).aspx

Here is an example of it from that page:

// Create an instance of a COM coclass:
FilgraphManager graphManager = new FilgraphManager();

// See if it supports the IMediaControl COM interface. 
// Note that this will throw a System.InvalidCastException if 
// the cast fails. This is equivalent to QueryInterface for 
// COM objects:
IMediaControl mc = (IMediaControl) graphManager;

// Now you call a method on a COM interface: 
mc.Run();

answered Mar 15, 2014 at 17:00

attila

2,2291 gold badge13 silver badges16 bronze badges

Collectives™ on Stack Overflow

How to mimick VB use of COM Object Interface using C#

2 Answers 2

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related