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Data Exchange

Posted on 2002-03-18
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Last Modified: 2013-11-20
info:
The MFC application I am writing has Database DAO file support.

Its called TheoFrontEnd

I have an edit box on my main form that is displaying the wrong value.

The control is:
IDC_EDIT_RecordCNT

Its member varible is:
long     m_RecordCNT;

The applications CTheoFrontEndView::OnInitialUpdate()function looks like this:
void CTheoFrontEndView::OnInitialUpdate()
{
        //start code generated by MFC
     m_pSet = &GetDocument()->m_theoFrontEndSet;
     CDaoRecordView::OnInitialUpdate();
     GetParentFrame()->RecalcLayout();
     ResizeParentToFit();
        //end code generated by MFC

        //start of my code
     m_pSet->MoveLast();
     m_RecordCNT=m_pSet->GetRecordCount(); //counts the number of records in the table I have linked to
        //end of my code
}

When I debug the app. the member variable m_RecordCNT DOES get the correct value!  However, that values does not show up in the edit box that the member variable is attached to.

From what I can tell the
void CTheoFrontEndView::DoDataExchange(CDataExchange* pDX)
function is never getting called. (maybe)

Or

Maybe I need to invalidate the rectangle that the edit box occupies.  I don't know.

What do you think?

Thanx
Ace
0
Comment
Question by:Smave
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6 Comments
 

Author Comment

by:Smave
ID: 6878745
OK.  After little more investigation the
void CTheoFrontEndView::DoDataExchange(CDataExchange* pDX)
is getting called.

But somehow the member variable
long     m_RecordCNT;
is getting reset to 0 after the
void CTheoFrontEndView::OnInitialUpdate()
is executed.

I moved the statement
 m_RecordCNT=m_pSet->GetRecordCount(); //counts the number of records in the table I have linked to
from the
void CTheoFrontEndView::OnInitialUpdate()
function to the
void CTheoFrontEndView::DoDataExchange(CDataExchange* pDX)
function.
Now the correct value does display in the edit box.

This fix works, but it is unacceptable.  I only need to count the records once, not every time the view is changed.

Why is the member variable loosing its value?

Thanx
Dave
0
 
LVL 49

Expert Comment

by:DanRollins
ID: 6878752
To transfer the data from a variable to a screen element, use
   UpdateData( FALSE );

This assumes that you have used ClassWizard to associate a m_RecordCNT with the edit control.  If so, there will be something like this in your DoDataExchange fn:

     DDX_Text(pDX, IDC_EDIT1, m_sEdit1);

-- Dan
0
 

Author Comment

by:Smave
ID: 6878816
Yes the class wizard did add:
DDX_Text(pDX, IDC_EDIT_RecordCNT, m_RecordCNT);
to the
void CTheoFrontEndView::DoDataExchange(CDataExchange* pDX)
function.

Somehow the
m_RecordCNT
member variable is loosing it values after the
void CTheoFrontEndView::OnInitialUpdate()
function is run.

I thought the member variable is global within the CTheoFrontEndView scope.

Ace
0
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Author Comment

by:Smave
ID: 6878829
Maybe this deserves 100 points.
0
 
LVL 49

Accepted Solution

by:
DanRollins earned 100 total points
ID: 6878853
Did you use  
   UpdateData( FALSE );
after assigning the desired value to m_RecordCNT?  There are other things to try, but that is the first and you did not mention trying it.

-- Dan
0
 
LVL 6

Expert Comment

by:peterdownes
ID: 6878887
Hi S,

As Dan has said, call UpdateData(FALSE);

The problem with your code is that CDaoRecordView::OnInitialUpdate() calls UpdateData(FALSE) before you set the value of m_RecordCNT

void CTheoFrontEndView::OnInitialUpdate()
{
   //start code generated by MFC
   m_pSet = &GetDocument()->m_theoFrontEndSet;
   CDaoRecordView::OnInitialUpdate();
   GetParentFrame()->RecalcLayout();
   ResizeParentToFit();
   //end code generated by MFC

   //start of my code
   m_pSet->MoveLast();
   m_RecordCNT=m_pSet->GetRecordCount(); //counts the number of records in the table I have linked
to
   UpdateData(FALSE);
   //end of my code
}

So the way to fix the problem is to add UpdateData as above.

Regards.
0

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