...scroll a Treeview when Drag/Drop?

procedure TForm1.TreeView1DragOver(Sender, Source: TObject; X, Y: Integer;
State: TDragState; var Accept: Boolean);
begin
if (y < 15) then {On the upper edge - should scroll up }
SendMessage(TreeView1.Handle, WM_VSCROLL, SB_LINEUP, 0)
else if (TreeView1.Height - y < 15) then { On the lower edge - should scroll down }
SendMessage(TreeView1.Handle, WM_VSCROLL, SB_LINEDOWN, 0);
end;

{+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
             ERWEITERUNG von / ENHANCEMENT sent by
           Stef Mientki (http://Punthoofd.flappie.nl)
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++}

{
Thomas Stutz wrote a code snippet, to scroll a treeview,
when dragging near top/bottom of a treeview.
But with his code, you had to keep your mouse moving.
Adding a timer, does the work for you.
}
....
  private
    { Private declarations }
    scroll_down   :boolean;
....

procedure TForm_test_list.tv_filesDragOver(Sender, Source: TObject; X, Y: Integer;
  State: TDragState; var Accept: Boolean);
(*******************************************************************************
Start auto scroll when draging near top or bottom
*******************************************************************************)
begin
  if y<15 then
  begin
    scroll_down:=true;
    timer_autoscroll.Enabled:=true;
  end
  else
    if (list.Height-y)<15 then
    begin
      scroll_down:=false;
      timer_autoscroll.Enabled:=true;
    end
    else timer_autoscroll.Enabled:=false;
end;

procedure TForm_test_list.Timer_autoscrollTimer(Sender: TObject);
(*******************************************************************************
Set timer to about 100 msec (disabled at initialization)
*******************************************************************************)
begin
  if scroll_down then
    SendMessage(tv_files.Handle, WM_VSCROLL, SB_LINEUP, 0)
  else
    SendMessage(tv_files.Handle, WM_VSCROLL, SB_LINEDOWN, 0);
end;

printed from
www.swissdelphicenter.ch
developers knowledge base