When an event occurs in a dialog box control, the control notifies the dialog box procedure by means of a WM_COMMAND message. The example in Creating a Square Meal Dialog Box processes notification messages from the combo box, the list box, and the OK button. The control identifier is in the low-order word of wParam, and the notification message is in the high-order word of wParam.
If the control identifier is IDCOMBO, an event has occurred in the combo box. In response, the dialog box procedure ignores all other combo box events except CBN_SELENDOK, which indicates that a selection was made, the drop down was closed up, and the changes made should be accepted. The dialog box procedure calls InitFoodList to reset the contents of the list box and to add the names of the current selection in the drop-down list box.
If the control identifier is IDLIST, an event has occurred in the list box. This causes the dialog box procedure to ignore all list box events except LBN_DBLCLK, which indicates that the user has double-clicked a list item. This event is processed in the same way as if an OK button has been chosen.
If the control identifier is IDOK, the user has chosen the OK button. In response, the dialog box procedure inserts the name of the selected food into the application's multi-line edit control, then calls the EndDialog function to close the dialog box.
If the control identifier is IDCANCEL, the user has clicked the Cancel button. In response, the dialog box procedure calls EndDialog to close the dialog box.