PRB: ATL Full Control Needs Enabled Stock Property for Access 97

• Microsoft Visual C++, 32-bit Editions, versions 5.0, 6.0
• Microsoft Access 97

SYMPTOMS

When opening a form that was saved in Access 97 and contains ActiveX controls developed with ATL, you might get a message box stating the following:

There is no object in this control.

CAUSE

This error can be caused when the control does not support the stock property for Enabled.

RESOLUTION

If you are developing a control using ATL and plan to use it in Microsoft Access, be sure to support the Enabled stock property. The ATL COM Object Wizard can add the needed code if you select Enabled from the list of available stock properties on the last property page when inserting the full control.

If you already have a control project that does not have the Enabled stock property selected, you can add support for it using the steps outlined here.

1. Determine whether or not your control has support for ANY stock properties. If not, modify the header file for the control to include support for ATL's default stock property support and comment out the IDispatchImpl derived class. For example:




class ATL_NO_VTABLE CATLAccessKBControl :
  public CComObjectRootEx<CComSingleThreadModel>,
//public IDispatchImpl<IATLAccessKBControl, &IID_IATLAccessKBControl,
\    //&LIBID_ATLACCESSCONTROLLib>,
public CStockPropImpl<CATLAccessKBControl, IATLAccessKBControl, \ 
          &IID_IATLAccessKBControl, &LIBID_ATLACCESSCONTROLLib>,
//rest of interfaces that are derived.... 

2. Modify the IDL file by adding support for propget/propput methods for DISPID_ENABLED. For example:




[
  object,
  uuid(91A905D0-8B9F-11D2-8F10-00C04F94089E),
  dual,
  pointer_default(unique)
]
interface IATLAccessKBControl : IDispatch
{
[propput, id(DISPID_ENABLED)] HRESULT Enabled([in]VARIANT_BOOL
   vbool);
[propget, id(DISPID_ENABLED)] HRESULT Enabled([out,retval] \ 
   VARIANT_BOOL*pbool);
}; 

3. Add a member variable to the control's header file, which will have the enabled stock property value. For example:




class ATL_NO_VTABLE CATLAccessKBControl :
  public CComObjectRootEx<CComSingleThreadModel>,
//rest of interfaces that are derived...
{
  public:
    BOOL m_bEnabled;
  //rest of class definition
}; 

Be sure to name the property "m_bEnabled" so ATL framework correctly sets it.

STATUS

This behavior is by design.

MORE INFORMATION

You do not get this problem with controls created with MFC or Visual Basic. Both of these products provide the Enabled stock property by default.

Steps to Reproduce Behavior

1. Create a new ATL COM AppWizard.



2. Select Dynamic Link Library (DLL) as the Server Type and accept the remaining defaults.



3. On the Insert menu, click New ATL Object.



4. Select controls from the category list on the left.



5. Select Full Control.



6. Give the control a name and accept the remaining defaults.



7. Build the control.



8. Start Access97 and open a database.



9. Insert a new form.



10. Insert the control and place it on the form.



11. Save the form and close it.



12. Attempt to re-open the form, and note that you receive a message box stating "There is no object in this control."

REFERENCES

For additional information, please click the article number below to view the article in the Microsoft Knowledge Base:

Q177105 ACC97: "No Object in This Control" Inserting Web Browser

Additional query words:

Keywords : kbnokeyword kbAccess97 kbATL210 kbCOMt kbContainer kbCtrlCreate kbVC500 kbVC600 kbATL300 kbDSupport kbGrpMFCATL
Version : WINDOWS:97; winnt:5.0,6.0
Platform : WINDOWS winnt
Issue type : kbprb