This code could be useful for example if you changed the wallpaper through code and need to refresh the desktop
Code:
//Method 1
uses
ShlObj;
procedure RefreshDesktop1;
begin
SHChangeNotify(SHCNE_ASSOCCHANGED, SHCNF_IDLIST, nil, nil);
end;
//Method 2
procedure RefreshDesktop2;
var
hDesktop: HWND;
begin
hDesktop := FindWindowEx(FindWindowEx(FindWindow('Progman', 'Program Manager'), 0,
'SHELLDLL_DefView', ''), 0, 'SysListView32', '');
PostMessage(hDesktop, WM_KEYDOWN, VK_F5, 0);
PostMessage(hDesktop, WM_KEYUP, VK_F5, 1 shl 31);
end;