How to detect if a TreeView has a scrollbar and how to change its position?

Problem/Question/Abstract:

How to detect if a TreeView has a scrollbar?
How to change the scrollbar in a TreeView (if it has one)?

Answer:

procedure TForm1.FormMouseWheelDown(Sender: TObject;
  Shift: TShiftState;
  MousePos: TPoint;
  var Handled: Boolean);

var
  iMin, iMax: Integer;
  bTreeViewVertScrollBarVisible: Boolean;

begin
  bTreeViewVertScrollBarVisible := True;
  GetScrollRange(Form1.TreeView1.Handle, SB_VERT, iMin, iMax);
  if iMin = iMax then
    bTreeViewVertScrollBarVisible := False; // No scrollbar visible

  if bTreeViewVertScrollBarVisible then
  begin
    iPos := GetScrollPos(Form1.TreeView1.Handle, SB_VERT);
    SetScrollPos(Form1.TreeView1.Handle, SB_VERT, iPos + 1, True);
    // Don't set Handled to True!
    // If you do that then ONLY the scrollbar changes but NOT the
    // content of the TreeView!
  end;

end;