LM_INSERTMULTITEMS inserts multiple items into a list box at one time, up to 32 768 items.

If either LIT_SORTASCENDING or LIT_SORTDESCENDING is specified in the lItemIndex field of LBOXINFO, then the complete list is sorted after the items have been inserted. If items are being added using several LM_INSERTMULTITEMS messages, it is faster to specify LIT_END for all the insert messages except the last one, and then set one of the sort flags to sort the entire list after the last set of items have been inserted.

The sorting sequence is the same as that defined for WinCompareStrings.

WM_MEASUREITEM (in List Boxes) is sent to the owner of an ownerdraw list box for every item inserted into the list box.