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.
| Parameter | Description |
| 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 | 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.