The WM_MEASUREITEM message is sent to the owner window of an owner-drawn button, combo box, list box, list view control, or menu item when the control or menu is created.
WM_MEASUREITEM
idCtl = (UINT) wParam; // control identifier
lpmis = (LPMEASUREITEMSTRUCT) lParam; // item-size information
If the value is zero, the message was sent by a menu. If the value is nonzero, the message was sent by a combo box or by a list box. If the value is nonzero, and the value of the itemID member of the MEASUREITEMSTRUCT pointed to by lpmis is (UINT) –1, the message was sent by a combo edit field.
If an application processes this message, it should return TRUE.
When the owner window receives the WM_MEASUREITEM message, the owner fills in the MEASUREITEMSTRUCT structure pointed to by the lParam parameter of the message and returns; this informs the system of the dimensions of the control. If a list box or combo box is created with the LBS_OWNERDRAWVARIABLE or CBS_OWNERDRAWVARIABLE style, this message is sent to the owner for each item in the control; otherwise, this message is sent once.
The system sends the WM_MEASUREITEM message to the owner window of combo boxes and list boxes created with the OWNERDRAWFIXED style before sending the WM_INITDIALOG message. As a result, when the owner receives this message, the system has not yet determined the height and width of the font used in the control; function calls and calculations requiring these values should occur in the main function of the application or library.
Windows NT: Requires version 3.1 or later.
Windows: Requires Windows 95 or later.
Windows CE: Requires version 1.0 or later.
Header: Declared in winuser.h.
Combo Boxes Overview, Combo Box Messages, MEASUREITEMSTRUCT, WM_INITDIALOG