PRB: CDaoRecordView Toolbar Buttons Malfunction

ID: Q150122

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, 4.2, 4.2b, 5.0, 6.0

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

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

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.

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.

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 );

Compile, build, and run the program.

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

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 kbDAO kbDatabase kbMFC kbVC kbVC400 kbVC410 kbVC420 kbVC500 kbVC600
Version : 4.00 4.10 4.20 4.20b 5.00
Platform : NT WINDOWS
Issue type : kbprb