PRB: CDaoRecordView Toolbar Buttons Malfunction

• The Microsoft Foundation Classes (MFC) included with: Microsoft Visual C++, 32-bit Edition, version 4.0, 4.1, 4.2, 4.2b, 5.0

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

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

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

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.

REFERENCES

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