Combo Box Types and Styles

Combo boxes can be characterized by type and style. Combo box types determine whether the combo box list is a drop-down list and whether the selection field is an edit control. A drop-down list appears only when the user opens it, so it uses less screen space than a list that is always visible. If the selection field is an edit control, the user can enter information not in the list; otherwise, the user can only select items in the list.

The following table shows the three combo box types and indicates whether each includes a drop-down list and an edit control:

Combo box type	Drop-down list	Edit control
Drop-down combo box	Yes	Yes
Drop-down list box	Yes	No
Simple combo box	No	Yes

Combo box styles define specific properties of a combo box. An application can combine styles; however some styles only apply to certain combo box types. The following table describes the combo box styles:

Style	Description
CBS_AUTOHSCROLL	Automatically scrolls the text in an edit control to the right when the user types a character at the end of the line. If this style is not set, only text that fits within the rectangular boundary is allowed.
CBS_DISABLENOSCROLL	Shows a disabled vertical scroll bar in the list box when the box does not contain enough items to scroll. Without this style, the scroll bar is hidden when the list box does not contain enough items.
CBS_DROPDOWN	Specifies a drop-down combo box.
CBS_DROPDOWNLIST	Specifies a drop-down list box.
CBS_HASSTRINGS	Specifies that an owner-drawn combo box contains items consisting of strings. The combo box maintains the memory and address for the strings so the application can use the CB_GETLBTEXT message to retrieve the text for a particular item.
CBS_LOWERCASE	Converts to lowercase all text in both the selection field and the list.
CBS_NOINTEGRALHEIGHT	Specifies that the size of the combo box is exactly the size specified by the application when it created the combo box. Normally, Windows sizes a combo box so that it does not display partial items.
CBS_OEMCONVERT	Converts text entered in the combo box edit control from the Windows character set to the OEM character set and then back to the Windows set. This ensures proper character conversion when the application calls the CharToOem function to convert a Windows string in the combo box to OEM characters. This style is most useful for combo boxes that contain filenames and applies only to combo boxes created with the CBS_SIMPLE or CBS_DROPDOWN style.
CBS_OWNERDRAWFIXED	Specifies that the owner of the list box is responsible for drawing its contents and that the items in the list box are all the same height. The owner window receives a WM_MEASUREITEM message when the combo box is created and a WM_DRAWITEM message when a visual aspect of the combo box has changed.
CBS_OWNERDRAWVARIABLE	Specifies that the owner of the list box is responsible for drawing its contents and that the items in the list box are variable in height. The owner window receives a WM_MEASUREITEM message for each item in the combo box when you create the combo box and a WM_DRAWITEM message when a visual aspect of the combo box has changed.
CBS_SIMPLE	Specifies a simple combo box.
CBS_SORT	Automatically sorts strings added to the list box.
CBS_UPPERCASE	Converts to uppercase all text in both the selection field and the list.

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