MFC - Combo Boxes


A combo box consists of a list box combined with either a static control or edit control. it is represented by CComboBox class. The list-box portion of the control may be displayed at all times or may only drop down when the user selects the drop-down arrow next to the control.

Here is the list of messages mapping for Combobox control −

Message Map entry Description
CBN_DBLCLK ON_CBN_DBLCLK( <id>, <memberFxn> ) The user double-clicks a string in the list box of a combo box.
CBN_DROPDOWN ON_CBN_DROPDOWN( <id>, <memberFxn> ) The list box of a combo box is about to drop down (be made visible).
CBN_EDITCHANGE ON_CBN_EDITCHANGE( <id>, <memberFxn> ) The user has taken an action that may have altered the text in the editcontrol portion of a combo box.
CBN_EDITUPDATE ON_CBN_EDITUPDATE( <id>, <memberFxn> ) The edit-control portion of a combo box is about to display altered text.
CBN_KILLFOCUS ON_CBN_KILLFOCUS( <id>, <memberFxn> ) The combo box is losing the input focus.
CBN_SELCHANGE ON_CBN_SELCHANGE( <id>, <memberFxn> ) The selection in the list box of a combo box is about to be changed as a result of the user either clicking in the list box or changing the selection by using the arrow keys.
CBN_SETFOCUS ON_CBN_SETFOCUS( <id>, <memberFxn> ) The combo box receives the input focus.

Let us look into an example of Radio button by creating a new MFC dialog based application.

Step 1 − Drag a Combo box and remove the Caption of Static Text control.

Remove Caption of Static Text

Step 2 − Add a control variable m_comboBoxCtrl for combobox and value variable m_strTextCtrl for Static Text control.

Step 3 − Add event handler for selection change of combo box.


Step 4 − Add the following code in OnInitDialog() to load the combo box.

for (int i = 0; i<10; i++) {
   str.Format(_T("Item %d"), i);

Step 5 − Here is the implementation of event handler.

void CMFCComboBoxDlg::OnCbnSelchangeCombo1() {
   // TODO: Add your control notification handler code here
   m_comboBoxCtrl.GetLBText(m_comboBoxCtrl.GetCurSel(), m_strTextCtrl);

Step 6 − When the above code is compiled and executed, you will see the following output.

Combobox Output

Step 7 − When you select any item then it will be displayed on the Text Control.