Writing a simple ActiveX control for IE that has one method

Question

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:

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!

Answer 1

You could mark your control as save for scripting by implementing IObjectSafety or by marking the Object as save while registering it (as supposed by the link you provided).

Have you run regsvr32 after adding the code to mark it save for scripting?

You can check the registry if your control has the safe for scripting bits set. If the bits are set you will find the two keys {7DD95802-9882-11CF-9FA9-00AA006C42C4} (Safe for Initialization) {7DD95801-9882-11CF-9FA9-00AA006C42C4}(Safe For Scripting) as subkeys of ImplementedCategories in your object.

I would suggest to implement IObjectSafety since it doesn't depend on your class to register itself.

Answer 2

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 :)