Owner Draw - ComboBox

Post date: Mar 15, 2010 9:17:02 PM

As with menus (menu items), an application can create an owner-drawn combo box to take responsibility for painting list items. An owner-drawn combo box can list/show information other than text strings - usually some graphical elements.

To create an owner-draw combo box, we set its Style property to csOwnerDrawFixed or csOwnerDrawVariable.

If all list items in the combo box are the same height, such as strings or icons, an application can use the csOwnerDrawFixed style.
If list items are of varying height, like bitmaps of different size, an application can use the csOwnerDrawVariable style. In this case the application will receive the WM_MEASUREITEM Windows message and the OnMeasureItem event will be fired for each item - to specify the height of list items in the combo box.

Having done this, Windows no longer draws the control. Instead it sends a WM_DRAWITEM message whenever a portion of the control needs to be repainted. The parent window (form) of an owner-drawn combo box (its owner) then fires the OnDrawItem event when a portion of the combo box needs to be painted.

To demonstrate owner-drawing with combo boxes create a combo box full of colors (two variations) and a combo with true-type fonts showing the actual image of the font.

To read more about Owner Drawing in Delphi read: http://delphi.about.com/od/vclusing/a/owner_drawing.htm

Only Delphi source code is included in the archive.