Delphi - Get and Set Scrollbar Position of a ListView

Save the top item before clearing,

FSaveTop := ListView1.TopItem;

After updating, scroll the listview so that the saved top item's 'y' position will be 0 (+ header height):

var
  R: TRect;
begin
  if Assigned(FSaveTop) then begin
    // account for header height
    GetWindowRect(ListView_GetHeader(ListView1.Handle), R);
    ListView1.Scroll(0, FSaveTop.Position.Y - (R.Bottom - R.Top));
  end;
end;

Actually, since you're re-populating the listview, you have to devise a mechanism to find which item you want to be at the top instead of saving a reference to it.

If you don't like modifying scroll position through 'top item', since functions like SetScrollInfo, SetScrollPos won't update the client area of the control, you can use GetScrollInfo to get the 'nPos' of a TScrollInfo before clearing the list, and then send that many WM_VSCROLL messages with 'SB_LINEDOWN` after populating.

Save scroll position:

var
  FPos: Integer;
  SInfo: TScrollInfo;
begin
  SInfo.cbSize := SizeOf(SInfo);
  SInfo.fMask := SIF_ALL;
  GetScrollInfo(ListView1.Handle, SB_VERT, SInfo);
  FPos := SInfo.nPos;
  ...

After populating, scroll (assuming scroll position is 0):

var
  R: TRect;
begin
  ...
  R := ListView1.Items[0].DisplayRect(drBounds);
  ListView1.Scroll(0, FPos * (R.Bottom - R.Top));

or,

var
  i: Integer;
begin
  ...
  for i := 1 to FPos do
    SendMessage(ListView1.Handle, WM_VSCROLL, SB_LINEDOWN, 0);