This message is sent by an application to a window in order to allow changes in that window to be redrawn, or to prevent changes in that window from being redrawn.
wParam
Specifies the state of the redraw flag. If the wParam parameter is nonzero, the redraw flag is set. If wParam is zero, the flag is cleared.
lParam
This parameter is not used.
This message sets or clears the redraw flag. However, it does not direct a list box to update its display. When the redraw flag is set, a control can be redrawn immediately after each change. When the redraw flag is cleared, no redrawing is done. Applications that need to add several names to a list without redrawing until the final name is added should set the redraw flag before adding the final name to the list.