Objective Grid: Displaying a messagebox during validation

Problem

How do I display a message-box from within OnValidateCell()?

Cause

Action

The easiest way is to override OnValidateCell() and call SetWarningText(). This technique is illustrated in the first example:

// Validate input
BOOL CDerGrid::OnValidateCell(ROWCOL nRow, ROWCOL nCol)
{
	CString s;
	CGXControl* pControl = GetControl(nRow, nCol);
	pControl->GetCurrentText(s);

	if (!s.IsEmpty( ))
	{
		if (_ttoi(s) < 1 || _ttoi(s) > 100)
		{
			SetWarningText (_T("Please enter a value between 1 and 100!"));
			return FALSE;
		}

		return TRUE;
	}

	return CGXGridView::OnValidateCell(nRow, nCol);
}

The second example displays a message box and also demonstrates how to correct the value or reset the cell to its previous value. Please note that we check the m_bLockActivateGrid before we display a message box. This avoids a message box being displayed when the grid loses focus because a user hit the "Cancel" key in a dialog.

BOOL CSample2GridWnd::OnValidateCell(ROWCOL nRow, ROWCOL nCol)
{
	CString s;
	// retrieve text from current cell
	CGXControl* pControl = GetControl(nRow, nCol);
	pControl->GetCurrentText(s);
 
	if (_ttol(s) < 0 || _ttol(s) > 100)
	{
		TCHAR sz[255];
		wsprintf(sz, _T("Please enter a value between 0 and 100!"));
		ScrollCellInView(nRow, nCol);

		// Display message box
		if (m_bLockActivateGrid)
		{
			AfxMessageBox(sz);

			// m_bWarningTextDisplayed is looked up in 
			// OnLButtonHitRowCol if you set this TRUE,
			// OnLButtonHitRowCol will cancel any further 
			// mouse processing
			m_bWarningTextDisplayed = TRUE;

			// If you want the current cell to be undone, call
			// TransferCurrentCell(FALSE);

			// This is only a sample. You might also display
			// a message box and ask the user if he wants to
			// retry or ignore the value or you could also
			// call pControl->SetCurrentText() to change
			// the value.
			// pControl->SetCurrentText("22");
		}

		// else do nothing, the focus will go back to the current cell
		return FALSE;
	}

	return TRUE;
}

The third example displays a message box and lets the user choose Yes, No or Cancel.

BOOL CGridSample9View::OnValidateCell(ROWCOL nRow, ROWCOL nCol)
{
	CString s;

	// Retrieve text from current cell
	CGXControl* pControl = GetControl(nRow, nCol);
	pControl->GetCurrentText(s);

	// Display message box
	if (m_bLockActivateGrid)
	{
		int result = AfxMessageBox(s, MB_YESNOCANCEL);

		// m_bWarningTextDisplayed is looked up in
		// OnLButtonHitRowCol.  If you set this TRUE,
		// OnLButtonHitRowCol will cancel any further
		// mouse processing
		m_bWarningTextDisplayed = TRUE;

		// If Yes then move to next cell.......
		if(result == IDYES)
			return TRUE;

		// If No then clear the current text and
		// return to the current cell
		else if(result == IDNO)
		{
			TransferCurrentCell(FALSE);
			return FALSE;
		}

		// If Cancel, then return to the current
		// cell for further editing.
		else if(result = IDCANCEL)
			return FALSE;
	}

	return TRUE;
}