Filling a List Box from a Second Recordset (MFC Data Access)
By default, a record view is associated with a single recordset object, whose fields are mapped to the record view's controls. Sometimes you might want to put a list box or combo box control in your record view and fill it with values from a second recordset object. The user can use the list box to select a new category of information to display in the record view. This topic explains how and when to do that.
Tip
Be aware that filling a combo box or list box from a data source might be slow. Take precautions against trying to fill a control from a recordset with a large number of records.
The model for this topic consists of a primary recordset that fills the controls of your form, while a secondary recordset fills a list box or combo box. Selecting a string from the list box causes your program to requery the primary recordset based on what was selected. The following procedure uses a combo box but applies equally to a list box.
To fill a combo box or list box from a second recordset
Create the recordset object (CRecordset for ODBC, CDaoRecordset for DAO).
Obtain a pointer to the CComboBox object for the combo box control.
Empty the combo box of any previous contents.
Move through all records in the recordset, calling CComboBox::AddString for each string from the current record you want to add to the combo box.
Initialize the selection in the combo box.
void CSectionForm::OnInitialUpdate()
{
// ...
// Fill the combo box with all of the courses
CENROLLDoc* pDoc = GetDocument();
if (!pDoc->m_courseSet.Open())
return;
// ...
m_ctlCourseList.ResetContent();
if (pDoc->m_courseSet.IsOpen())
{
while (!pDoc->m_courseSet.IsEOF() )
{
m_ctlCourseList.AddString(
pDoc->m_courseSet.m_CourseID);
pDoc->m_courseSet.MoveNext();
}
}
m_ctlCourseList.SetCurSel(0);
}
This function uses a second recordset, m_courseSet, which contains a record for each course offered, and a CComboBox control, m_ctlCourseList, which is stored in the record view class.
The function gets m_courseSet from the document and opens it. Then it empties m_ctlCourseList and scrolls through m_courseSet. For each record, the function calls the combo box's AddString member function to add the course ID value from the record. Finally, the code sets the combo box's selection.