How to Exclude CLSIDs from OLE's Insert Object Dialog (120682)

SUMMARY

When building a container/server application with the Microsoft Foundation OLE Classes, you should prohibit the application user from inserting an object of the type serviced by the application itself. In fact, with an MDI application, if you try to embed your server's object in your server's document, you'll get the following message and trace messages indicating that a QueryInterface call failed:

Message box statement:

   Failed to create object. Make sure that the object is entered
   in the system registry.

Trace messages:

   Warning: constructing COleException, scode = E_NOINTERFACE ($80000004)
   Warning: Throwing an Exception of type COleException"

This article gives an example showing how to customize the OLE Insert Object dialog wrapped by the COleInsertDialog class. This customization omits your server object's class id from the selection list so the user won't be able to embed it.

MORE INFORMATION

The COleInsertDialog class contains a member m_io -- as described in online help for the OLE Classes:

   COleInsertDialog::m_io

   Structure of type OLEUIINSERTOBJECT used to control the
   behavior of the Insert Object dialog box. Members of
   this structure can be modified either directly or
   through member functions.

The OLEUIINSERTOBJECT dialog contains two members which allow the user to exclude specific object types from the dialog's selection list by CLSID. The member lpClsidExclude is a pointer of type LPCLSID and therefore must point directly to a variable of type CLSID. The member cClsidExclude is a UINT and contains the number of CLSID types that are pointed to by lpClsidExclude. If you want to exclude more than one CLSID, use an array.

The sample code below demonstrates how to exclude the AppWizard generated CLSID for the application's own object. This CLSID can be found in the CWinApp-derived class implementation file as the static global variable "clsid" and will look something like this:

// This identifier was generated to be statistically unique for your app.
// You may change it if you prefer to choose a specific identifier.
static const CLSID BASED_CODE clsid = {   0x565295c6, 0xc992, 0x11cd,
                        { 0x96, 0xf2, 0x0, 0xaa, 0x0, 0x3b, 0x80,0x67 } };

For the purpose of accessing clsid from a view class member function, take the "static" storage class off the above declaration.

You can then assign the lpClsidExclude pointer to &clsid from any module in the program. For the purpose of this sample, cClsidExclude is a count of one, so no array will be used.

The code to assign these members must be run before displaying the dialog. Therefore it's best to assign these members in the container view class' OnInsertObject() member. The OnInsertObject() shown in the sample code below is based on the one that AppWizard provides.

Sample Code

/* AppWizard generated OnInsertObject() function modified to
 * exclude our own object type from the OLE Insert Object Dialog.
 */ 
void CSvrcntrView::OnInsertObject()
{
    // Invoke the standard Insert Object dialog box to obtain information
    //  for new CSvrcntrCntrItem object.
    COleInsertDialog dlg;
    // Our own object's clsid - don't insert it!
    dlg.m_io.lpClsidExclude = (LPCLSID) &clsid;
    dlg.m_io.cClsidExclude = 1;    // Number of clsid's in the array.

    if (dlg.DoModal() != IDOK)
        return;

    BeginWaitCursor();

    CSvrcntrCntrItem* pItem = NULL;
    TRY
    {
        // Create new item connected to this document.
        CSvrcntrDoc* pDoc = GetDocument();
        ASSERT_VALID(pDoc);
        pItem = new CSvrcntrCntrItem(pDoc);
        ASSERT_VALID(pItem);

        // Initialize the item from the dialog data.
        if (!dlg.CreateItem(pItem))
            AfxThrowMemoryException();  // any exception will do
        ASSERT_VALID(pItem);

        // If item created from class list (not from file) then launch
        //  the server to edit the item.
        if (dlg.GetSelectionType() == COleInsertDialog::createNewItem)
            pItem->DoVerb(OLEIVERB_SHOW, this);

       ASSERT_VALID(pItem);

        // As an arbitrary user interface design, this sets the selection
        //  to the last item inserted.

        // TODO: reimplement selection as appropriate for your application

        m_pSelection = pItem;   // set selection to last inserted item
        pDoc->UpdateAllViews(NULL);
    }
    CATCH(CException, e)
    {
        if (pItem != NULL)
        {
            ASSERT_VALID(pItem);
            pItem->Delete();
        }
        AfxMessageBox(IDP_FAILED_TO_CREATE);
    }
    END_CATCH

    EndWaitCursor();
}