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POHandling a VB6 event in C# - why does it only work sometimes?
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copied!<p>I have a VB6 application implemented as an ActiveX exe. I also have a C# application that interacts with the VB6 app via COM.</p> <p>This all works fine except in one scenario.</p> <p>If the VB6 app is kicked off from the C# app, everything is fine. If, however, the VB6 app is already running stand-alone, then although the COM interface still works, the C# event handlers never fire. </p> <p>A (very simplified) extract of the code follows, names & GUIDs changed to protect the innocent.</p> <p>VB6 app: myVB6App.cls (GlobalSingleUse)</p> <pre><code>Event myEvent() public function RaiseMyEvent() RaiseEvent myEvent end function </code></pre> <p>(partial) IDL generated from the built VB6 exe:</p> <pre><code>... [ uuid(xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx), version(1.10), appobject ] coclass myApp { [default] interface _myApp; [default, source] dispinterface __myApp; }; ... [ uuid(yyyyyyyy-yyyy-yyyy-yyyy-yyyyyyyyyyyy), version(1.10), hidden, nonextensible ] dispinterface __myApp { properties: methods: ... [id(0x00000005)] void myEvent(); ... }; ... </code></pre> <p>C# app:</p> <pre><code>public class myAppInterface : IDisposable, ImyAppEvents { public delegate void myEventDelegate(); public event myEventDelegate myEventHandler; private object _myApp = null; private IConnectionPoint _connectionPoint; private int _sinkCookie; public myAppInterface() { _myApp = Activator.CreateInstance(Type.GetTypeFromProgID("myVB6ProjectName.myApp")); Guid g = new Guid("yyyyyyyy-yyyy-yyyy-yyyy-yyyyyyyyyyyy"); connectionPointContainer.FindConnectionPoint(ref g, out _connectionPoint); _connectionPoint.Advise(this, out _sinkCookie); } public void myEvent() { if (myEventHandler != null) { myEventHandler(); } } } [ComImport, Guid("yyyyyyyy-yyyy-yyyy-yyyy-yyyyyyyyyyyy"), TypeLibType((short)4240)] [InterfaceTypeAttribute(ComInterfaceType.InterfaceIsIDispatch)] public interface ImyAppEvents { [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime), DispId(5)] void myEvent(); } public class myC#App { private static myAppInterface _vb6App; public static myAppInterface VB6Application { get { if (_vb6App == null) { _vb6App = new myAppInterface(); _vb6App.myEventHandler += new myAppInterface.myEventDelegate(DoSomething); } return _vb6App; } } static void DoSomething() { //code to actually handle the event } } </code></pre> <p>As I say, if at the point that <code>Activator.CreateInstance</code> runs, the VB6 exe is not currently running, everything work as expected and the code in <code>DoSomething()</code> is executed when <code>myEvent</code> is fired in the VB6 app. </p> <p>If the VB6 app is running stand-alone beforehand, the C# app can still control it via COM (methods not shown above for clarity) but the <code>DoSomething()</code> code never runs in response to <code>myEvent</code>.</p> <p>Any ideas where I'm going wrong?</p>

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