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Editorial Team
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Asked: 2026-05-16T10:14:47+00:00

I’m learning how to write a scriptable ActiveX control. My goal is to have

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I’m learning how to write a scriptable ActiveX control. My goal is to have a tiny control that can check to see if something is installed on the system. What I’ve done so far is:

  • Create a MFC ActiveX control project in VS2008
  • Add some ‘safe for scripting’ bits that I found here.
  • Extend the IDL to provide my “IsInstalled” method, which for now returns TRUE unconditionally (but will later read some keys from the registry.)
  • Build the control and run regsvr32 on it. I verified that it does show up in HKEY_CLASSES_ROOT, and when I instantiate the object, the IE Developer Tools “Locals” pane shows that the object is of type _D[my plugin name]. Not only that, but my IsInstalled() method shows up underneath that object.

However, when I call IsInstalled(), I just can’t get it to work:

JScript Debugger – Breaking on JScript runtime error -(n http://img138.imageshack.us/img138/1586/whycomwhy.png

I’m at a loss. I’ve also tried making IsInstalled a property instead of a method, using VARIANT_BOOL instead of boolean instead of BOOL in the IDL, you name it.

Here’s the relevant excerpts of code.

The header:

afx_msg VARIANT_BOOL IsInstalled();

The implementation:

afx_msg VARIANT_BOOL
CMyAXCtrl::IsInstalled()
{
   return TRUE;
}

The dispatch map:

BEGIN_DISPATCH_MAP(CMyAXCtrl, COleControl)
   DISP_FUNCTION_ID(CMyAXCtrl, "IsInstalled", dispidIsInstalled, IsInstalled, VT_BOOL, VTS_NONE)
END_DISPATCH_MAP()

The dispatch part of the IDL:

   [ uuid(6B662202-CF13-4144-AA33-C3FEE9C2C962),
      helpstring("Dispatch interface for My Control")]
   dispinterface _Daxplugin
   {
   properties:
   methods:
      [id(1)] VARIANT_BOOL IsInstalled();
   };

If there’s any other relevant bits of code I should provide, let me know. But I’m stumped here. Thank you in advance!

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1 Answer

  1. Editorial Team

    You almost certainly have the wrong prototype for a scriptable function. OLE Automation for scripting languages tends to rely on returning a HRESULT then using an out parameter for the actual return code.

    So change it to
    [id(1)] HRESULT IsInstalled(VARIANT_BOOL* p);

    Also TRUE != VARIANT_TRUE, you must return VARIANT_TRUE which is equal to -1 instead of 1.

    Hope some of that actually helps, but without the actual error I might be mistaken 🙂

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