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 Windows 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.
Windows 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, Windows 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.
|file: /Techref/os/win/api/win32/mess/src/msg25_23.htm, 2KB, , updated: 2000/4/7 12:20, local time: 2022/5/16 09:14,
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