Q153581: HOWTO: Implement the Type Property of a Custom OLE Control

Article: Q153581
Product(s): Microsoft Visual Basic for Windows
Version(s): 
Operating System(s): 
Keyword(s): 
Last Modified: 05-MAY-2001

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The information in this article applies to:

- Microsoft Visual Basic Standard Edition, 32-bit, for Windows, version 4.0 
- Microsoft Visual Basic Professional Edition, 16-bit, for Windows, version 4.0 
- Microsoft Visual Basic Professional Edition, 32-bit, for Windows, version 4.0 
- Microsoft Visual Basic Enterprise Edition, 16-bit, for Windows, version 4.0 
- Microsoft Visual Basic Enterprise Edition, 32-bit, for Windows, version 4.0 
- Microsoft Visual C++, 32-bit Enterprise Edition, version 4.x 
- Microsoft Visual C++, 32-bit Professional Edition, version 4.x 
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SUMMARY
=======

The type of an OLE control is the coclass name for the OLE control as defined in
its ODL file. For example, the type of Textbox control is TextBox, the type of
the Data Bound Grid control from Apex is DBGrid, and so on. In Visual Basic, the
type of an OLE Control appears to the right of the control name in the Editbox
portion of the property browser. This article shows how you can implement a
custom Type property for a custom OLE control that returns its type.

MORE INFORMATION
================

Step-by-Step Example
--------------------

1. Create a rudimentary 32-bit OLE Control using the MFC CDK that ships with
  Visual C++ 4.x. This article assumes that this custom OCX is called Test
  (coclass name) and that the control class name is CTestCtrl.

2. Use the Visual C++ MFC ClassWizard to add the following Property to your
  control class. The external name of this Property is Type. It is implemented
  as a Get method only (called GetControlType), so it is a read-only property.
  It takes no parameters and returns the type as a BSTR. The implementation of
  this Get method calls an internal private member function of the control
  class called GetCtrlType() that does all the work.

  You will also need to add a protected member variable m_bstrType (to actually
  hold the type name as a BSTR) and a protected member function GetCtrlType()
  to the control class in the header file as follows:

        Class CTestControl::COleControl
           {
            .
            .
            .

            protected:
            BSTR m_bstrType;
            BSTR GetCtrlType (void);
            }

3. Add the following code to the implementation file (.CPP) of the control
  class:

  ////////////////////////////////////////////////////////////////////// 
        // CTestCtrl::CTestCtrl - Constructor

        CTestCtrl::CTestCtrl()
        {
           InitializeIIDs(&IID_DTest, &IID_DTestEvents);

           // TODO: Initialize your control's instance data here.

           m_bstrType = NULL;

           .
           .
           .
         }

  ////////////////////////////////////////////////////////////////////// 
        // CTestCtrl::~CTestCtrl - Destructor

        CTestCtrl::~CTestCtrl()
        {
           // TODO: Cleanup your control's instance data here.

           if (m_bstrType)
              SysFreeString(m_bstrType);

           .
           .
           .
         }

         BSTR CTestCtrl::GetCtrlType (void)
         {

             IProvideClassInfo *pProvideClassInfo;
             LPTYPEINFO pTypeInfo;

             if(GetIDispatch(FALSE)->QueryInterface(IID_IProvideClassInfo,
               (LPVOID   *)&pProvideClassInfo) ==  NOERROR)
            {
               if (pProvideClassInfo->GetClassInfo(&pTypeInfo) == NOERROR)
               {
                  if (m_bstrType)
                     SysFreeString(m_bstrType);

                  pTypeInfo->GetDocumentation(MEMBERID_NIL, &m_bstrType,
                                              NULL, NULL, NULL);
                  pTypeInfo->Release();
               }

               pProvideClassInfo->Release();
            }

            return m_bstrType;
         }

         BSTR CTestCtrl::GetControlType()
         {
            CString strResult;
            // TODO: Add your property handler here

            strResult = GetCtrlType();
            return strResult.AllocSysString();
         }

4. Build the Test OLE control from Visual C++ 4.x, which should automatically
  register the control if everything compiles properly.

5. From Visual Basic 4.0 32-bit, open a new project, and add the Test OLE
  control to the Visual Basic toolbox by choosing it from the Tools Custom
  Controls menu.

6. Add an instance of the Test OLE control to Form1. This will be named Test1.

7. Add the following code to the general declarations portion of Form1:

     Private Sub Form_Click()
        Debug.Print Test1.Type
     End Sub

8. Run the Visual Basic program, and click the form. You should see Test printed
  in the Debug window

Additional query words: 4.00 vb4win vb4all vbctrl

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Keywords          :  
Technology        : kbVCsearch kbVBSearch kbAudDeveloper kbVB400Search kbVB400 kbVB16bitSearch kbVC32bitSearch
Issue type        : kbhowto

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