ID Number: Q66479
3.00
WINDOWS
Summary:
The WM_SETREDRAW message can be used to set and clear the redraw flag
for a window. Before an application adds many items to a list box,
this message can be used to turn the redraw flag off, which prevents
the list box from being painted after each addition. Properly using
the WM_SETREDRAW message keeps the list box from flashing after each
addition.
More Information:
The following four steps outline ways to use the WM_SETREDRAW message
to facilitate making a number of changes to the contents of a list box
in a visually pleasing manner:
1. Clear the redraw flag by sending the list box a WM_SETREDRAW
message with wParam set to FALSE. This prevents the list box from
being painted after each change.
2. Send appropriate messages to make any desired changes to the
contents of the list box.
3. Set the redraw flag by sending the list box a WM_SETREDRAW message
with wParam set to TRUE. The list box does not update its display
in response to this message.
4. Call InvalidateRect(), which instructs the list box to update its
display. Set the third parameter to TRUE to erase the background in
the list box. If this is not done, if a short list box item is
drawn over a long item, part of the long item will remain visible.
The following code fragment illustrates the process described above:
/* Step 1: Clear the redraw flag. */
SendMessage(hWndList, WM_SETREDRAW, FALSE, 0L);
/* Step 2: Add the strings. */
for (i = 0; i < n; i++)
SendMessage(hWndList, LB_ADDSTRING, ...);
/* Step 3: Set the redraw flag. */
SendMessage(hWndList, WM_SETREDRAW, TRUE, 0L);
/* Step 4: Invalidate the list box window to force repaint. */
InvalidateRect(hWndList, NULL, TRUE);
Additional reference words: 3.00 SR# G900921-44 flash flicker