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Article: Q150122
Product(s): Microsoft C Compiler
Version(s): 4.00 4.10 4.20 4.20b 5.00
Operating System(s): 
Keyword(s): kbcode kbusage kbDAOsearch kbDatabase kbMFC kbVC kbVC400 kbVC410 kbVC420 kbVC500 kbVC60
Last Modified: 03-AUG-2001

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The information in this article applies to:

- The Microsoft Foundation Classes (MFC), included with:
   - Microsoft Visual C++, 32-bit Editions, versions 4.0, 4.1 
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 4.2 
   - Microsoft Visual C++, 32-bit Professional Edition, version 4.2 
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 4.2b 
   - Microsoft Visual C++, 32-bit Professional Edition, version 4.2b 
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 5.0 
   - Microsoft Visual C++, 32-bit Professional Edition, version 5.0 
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 6.0 
   - Microsoft Visual C++, 32-bit Professional Edition, version 6.0 
   - Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
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SYMPTOMS
========

CDaoRecordView depends on an instance of CDaoRecordset to display data. The
CDaoRecordView class also needs to stay in synchronization with the current
record displayed by the CDaoRecordset instance. Calling the Seek, MoveFirst,
MoveNext, or other methods directly on the CDaoRecordset being used by a
CDaoRecordView causes the CDaoRecordView to behave incorrectly.

CAUSE
=====

CDaoRecordView uses four member variables to keep track of bookkeeping
information. The first three variables listed below store bookmarks for the
first, last, and current record. The fourth variable is used to enable or
disable the toolbar buttons corresponding to MoveFirst, MovePrev, MoveNext, and
MoveLast.

  m_varBookmarkCurrent
  m_varBookmarkFirst
  m_varBookmarkLast
  m_nStatus

These variables are only maintained when the CDaoRecordView::OnMove method is
invoked. This method invokes the CDaoRecordset MoveFirst, MoveNext,
MovePrevious, or MoveLast methods, and updates the variables. Only OnMove keeps
these variables in synchronization.

The following list contains the more common CDaoRecordset methods that change the
current record:

  - Find            - Move            - Requery
  - FindFirst       - MoveFirst       - Seek
  - FindLast        - MoveLast        - SetAbsolutePosition
  - FindNext        - MoveNext        - SetBookmark
  - FindPrev        - MovePrev        - SetPercentPosition

When the AddNew method is called, a new record is added to the recordset but the
current record bookmark does not change. To change the newly added record to the
current record, use the following method:

     // set the current bookmark to the newly added record
     m_pSet->SetBookmark(GetLastModifiedBookmark());

NOTE: GetLastModifiedBookmark() needs to be called right after the call to
Update() to return the newly added record. Calling it after one of the
recordview MoveXXXX functions returns a bookmark to the record that was current
prior to the move operation.

RESOLUTION
==========

After performing a CDaoRecordset method for an instance utilized by
CDaoRecordView, reset the CDaoRecordView's bookkeeping variables as shown in the
following code:

     if (!m_pSet->Seek(...))
     {
       if( !m_pSet->IsEOF() )
       {
           m_varBookmarkCurrent = 1L;   // <<- re-initialize
           m_varBookmarkFirst =         // <<- the bookmark
              m_varBookmarkLast = 0L;   // <<- member variables!
          // Enable toolbar buttons
          m_nStatus |= AFX_DAOVIEW_SCROLL_BACKWARD;// First & Prev buttons
          m_nStatus |= AFX_DAOVIEW_SCROLL_NEXT;    // next toolbar button
          m_nStatus |= AFX_DAOVIEW_SCROLL_LAST;    // last toolbar button
       }
       else
       {
          // Move to some valid record
       }
    }
    else
    {
       // Seek failed - move to a valid record
    }

STATUS
======

This behavior is by design.

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

Steps to Reproduce Behavior
---------------------------

1. Generate a default AppWizard application named SeekTest, and give it the
  following attributes:

   - Database View without File Support.

   - Select a data source, using DAO and a Table recordset type.

   - Open the Student Registration database (STDREG32.MDB) on the SECTION
     table.

2. Using the Resource View, add several text boxes to the IDD_SEEKTEST_FORM
  dialog resource that appears. Use the CTRL-DBLCLK short-cut to bind columns
  in SECTION to the dialog resource.

3. Add a button to the IDD_SEEKTEST_FORM resource. Using ClassWizard, add the
  following code:

        m_pSet->SetCurrentIndex( _T("PrimaryKey") );

        COleVariant varCourse ( _T("MATH201"), VT_BSTRT );
        COleVariant varSection( _T( "1"     ), VT_BSTRT );

        if(! m_pSet->Seek( _T( "=" ), &varCourse, &varSection ) )
        {
            // Seek failed - need to move to a valid record
            m_pSet->MoveFirst();
        }
        UpdateData( FALSE );

4. Compile, build, and run the program.

5. Click the MoveNext (>) button and then the MovePrevious (<) button to
  disable the MoveFirst (|<) and MovePrevious (<) toolbar buttons.

6. Click the Seek button. Note that the MoveFirst and MovePrevious buttons are
  still incorrectly disabled.

Adding the code to clear the bookmarks, and resetting the m_nStatus variable
corrects the toolbar and prevents other problems.

REFERENCES
==========

For additional information, please see the following articles in the Microsoft
Knowledge Base:

  Q145686 CDaoRecordView Bookmark Members Invalid After Requery()

  Q145719 DAOENROL - Can't See Added Records in Windows 95

Additional query words:

======================================================================
Keywords          : kbcode kbusage kbDAOsearch kbDatabase kbMFC kbVC kbVC400 kbVC410 kbVC420 kbVC500 kbVC600 
Technology        : kbAudDeveloper kbMFC
Version           : 4.00 4.10 4.20 4.20b 5.00
Issue type        : kbprb

=============================================================================

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Q150122: PRB: CDaoRecordView Toolbar Buttons Malfunction