Vb6.ActiveX.Hosting 0.1.0

Vb6.ActiveX.Hosting

Host VB6 ActiveX DLL modeless and modal forms inside a .NET process. ComHost.Open() starts a dedicated STA thread and message pump (MTA callers are fine). You do not register an OLE message filter or pump messages yourself.

Windows-only. Classic 32-bit VB6 DLLs must be loaded from an x86 (or AnyCPU prefer-32-bit) process.

Install

dotnet add package Vb6.ActiveX.Hosting

Sync

using (ComHost host = ComHost.Open())
{
  host.ModelessWindowOpened += (_, e) => { /* not on the host STA thread */ };
  dynamic launcher = host.CreateInstance("YourLib.YourClass");
  launcher.ShowNonModal();
}

CreateInstance (non-generic) returns a late-bound proxy: ShowModal / ShowNonModal run on the host STA thread, so a modal form can be closed with the title-bar close box or CloseWindows(). The host tracks each RCW and releases it on Dispose (or earlier via Release). Do not call Marshal.ReleaseComObject. CreateInstance<T> returns the raw RCW — call UI methods through Invoke / InvokeAsync.

Show vbModal blocks the caller until the form closes. From another thread, CloseWindows() or HostWindowEventArgs.Close() posts WM_CLOSE.

Async

await using (ComHost host = ComHost.Open())
{
  await host.InvokeAsync(() =>
  {
    dynamic launcher = host.CreateInstance("YourLib.YourClass");
    launcher.ShowModal();
  });
}

InvokeAsync does not block the caller. await using calls DisposeAsync.

Options

ComHostOptions options = new ComHostOptions
{
  EventContext = SynchronizationContext.Current, // WinForms/WPF UI thread
  ShutdownTimeout = TimeSpan.FromSeconds(2),
  Logger = logger,
};

using (ComHost host = ComHost.Open(options))
{
  foreach (HostWindowInfo window in host.GetWindows())
  {
    _ = window.Title;
  }
}

Activation failures throw ComHostException (ProgID/CLSID, HRESULT, regsvr32 hint). A 64-bit process throws PlatformNotSupportedException unless ThrowIf64BitProcess is false.

Requirements

• Windows, .NET Standard 2.0 or .NET 8+ Windows
• 32-bit process when loading 32-bit VB6 DLLs in-process
• The ActiveX DLL registered (regsvr32 from SysWOW64) or registration-free COM

Sample app and VB6 sources: github.com/jeromydean/VB6ComHost.