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I have implemented an Automation Server in Delphi XE7 according to the code from the Eric Harmon Delphi COM programming book but I can't get COM events to work running on Windows 10.

The automation server has been setup for CiMultiInstance, so one server for multiple clients. The main class implements IConnectionPointContainer. In the Initialize method, I create FConnectionPoints and the FConnectionPoints.CreateConnectionPoint is called successfully. It also successfully calls RegisterActiveObject.

It works fine when calling the server methods, and it has an Events interface but when it tries to send data back to the client, it calls GetEnumerator and falls over at the QueryInterface(IConnectionPointContainer,Container) call.

I have run the server up from an elevated Command line but it makes no differences.

This is the first line of the class:

    TMRILocalProxyServer = class(TAutoObject, IConnectionPointContainer, IMRILocalProxyServer)

The IMRILocalProxyServer_TLB includes an event and has component wrappers so for instance there is an InvokeEventMethod.

procedure TMRILocalProxyServer.InvokeEvent(DispID: TDispID; var Params: TVariantArray);
begin
  case DispID of
    -1: Exit;  // DISPID_UNKNOWN
    203: if Assigned(FOnReturnData) then
         FOnReturnData(Self, Params[0] {OleVariant});
  end; {case DispID}
end;

In the client code the OnReturnData has been assigned to a method.

This is part of the Initialize method:

  FConnectionPoints := TConnectionPoints.Create(Self);
  if AutoFactory.EventTypeInfo <> nil then
    begin
      FConnectionPoints.CreateConnectionPoint(AutoFactory.EventIID, ckMulti, EventConnect);
      OleCheck(RegisterActiveObject(Self as IUnknown, CLASS_MRILocalProxyServer_, ActiveObject_Weak, FROTCookie))
    end

This is the code that fails, the first code line of this function.

function TMRILocalProxyServer.GetEnumerator: IEnumConnections;
var
  Container : IConnectionPointContainer;
  ConnectionPoint : IConnectionPoint;
begin
  OleCheck(QueryInterface(IConnectionPointContainer,Container));

 OleCheck(Container.FindConnectionPoint(Autofactory.EventIID,ConnectionPoint));
  ConnectionPoint.EnumConnections(Result);
end;

The error it is coming up with is '...raised exception class $C0000005 with message 'c0000005 ACCESS_VIOLATION'.

Looking at the two variables, they show as 00000000 i.e. nil.

One last thing, this is compiled for 64-bit code.

David Bolton
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  • Do youu get the AV if you include your code in a minimal 32-bit application? – MartynA Jul 12 '19 at 15:13
  • Yes, I recompiled and just ran it. The same error. Also If I run it on Windows 2016 it's a catastrophic exception!. – David Bolton Jul 12 '19 at 15:23
  • Well, until this is sorted out, personally I'd stick with 32bit on Win10 (I've never had any major problems with setting up client-side event handling). Next thing I'd do is to run the client under the IDE debugger and see if I could trace why the event handling object isn't being correctly created, as that seems the likely source of the error. – MartynA Jul 12 '19 at 16:05
  • I think you need to add a [minimal, reproducible example](https://stackoverflow.com/help/minimal-reproducible-example) to your q. Meanwhile, you might compare your event-sinking code with mine in my answer here: https://stackoverflow.com/questions/25527367/detect-when-the-active-element-in-a-twebbrowser-document-changes/25529412 - mine worked fine compiled to 32-bit on Win10. – MartynA Jul 12 '19 at 18:52
  • I suspect it is thread related. Even though I have used CoInitialize (it's all STA). This is occurring in an automation server that sends and receives messages via TCP using Indy. Multiple clients of my automation server connect and send messages; the automation server sends them down the wire. There's another automation server proxy at the other end doing the same. I use a timer in each proxy to poll the TCP endpoint and it should send the message back to the client. I suspect this is where my problem lies. Creating a simple example may be tricky! – David Bolton Jul 15 '19 at 08:16
  • I have fixed it. There were two issues. One was I hadn't used STA everywhere and needed to add CoInitialize in one place. The other was a timing issue. It's a complicated piece of code with a form that opens and gets a reference to the automation server. I had to add a timer on the form to query a variable set in Initialize. Once I did that, it all worked. – David Bolton Jul 17 '19 at 07:03

0 Answers0