TScrollBox without scrollbars - delphi

Question

I want to dynamically create some buttons in a TScrollBox (that has VertScrollBar.Vissible= False).
I want to programmatically bring some of those buttons in view, so I would like to use something like:
ScrollBox.VertScrollBar.Position:= i; //Does not work
However, the box won't scroll to the indicated position unless the VertScrollBar.Vissible= True.
Note: ScrollBy() works, but I don't want to use that.
How to circumvent this behavior?
(A "solution" would be to let the scrollbars visible and hide them outside the screen (place the scrollbox in a panel))
Code:
unit UnitVert;
interface
uses
System.SysUtils, System.Classes, Vcl.Graphics, Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls;
type
TForm3 = class(TForm)
ScrollBox1: TScrollBox;
Button1: TButton;
Button2: TButton;
procedure Button2Click(Sender: TObject);
end;
var
Form3: TForm3;
implementation {$R *.dfm}
procedure TForm3.Button2Click(Sender: TObject);
begin
ScrollBox1.VertScrollBar.Position:= -20;
//ScrollBox1.ScrollBy(0, -20); //Works
end;
end.
object Form3: TForm3
Left = 0
Top = 0
Caption = 'Form3'
ClientHeight = 336
ClientWidth = 635
Color = clBtnFace
Font.Charset = DEFAULT_CHARSET
Font.Color = clWindowText
Font.Height = -11
Font.Name = 'Tahoma'
Font.Style = []
OldCreateOrder = False
PixelsPerInch = 96
TextHeight = 13
object ScrollBox1: TScrollBox
Left = 176
Top = 75
Width = 283
Height = 203
HorzScrollBar.Visible = False
VertScrollBar.Visible = False
TabOrder = 0
object Button1: TButton
Left = 188
Top = 132
Width = 123
Height = 99
Caption = 'Dummy'
TabOrder = 0
end
end
object Button2: TButton
Left = 26
Top = 50
Width = 111
Height = 51
Caption = 'Test'
TabOrder = 1
OnClick = Button2Click
end
end

Answer 1

Works as expected
Cannot reproduce your issue with D7 on Win7:
Scrollbox1.HorzScrollBar.Visible:= FALSE;
Scrollbox1.VertScrollBar.Visible:= FALSE;
Scrollbox1.ScrollBy( -30, -45 );
...moves the viewport 30 px to the left and 45 px to the top. Also note that the first parameter is X (horizontal) and the second parameter is Y (vertical) - actually anything I've seen in life was always in the X,Y order.
Why invisible scrollbars won't work
The method TWinControl.ScrollBy() includes this code:
IsVisible := (FHandle <> 0) and IsWindowVisible(FHandle);
if IsVisible then ScrollWindow(FHandle, DeltaX, DeltaY, nil, nil);
...which means: it is essentially using the WinAPI's ScrollWindow() function. Changing the position of one of the scrollbars executes TControlScrollBar.SetPosition(), which in turn calls .ScrollBy() again for just one dimension:
OldPos := FPosition;
if Kind = sbHorizontal then
FControl.ScrollBy(OldPos - Value, 0) else
FControl.ScrollBy(0, OldPos - Value);
...and since this time the parent control is the scrollbar (not the scrollbox) its invisibility prevents the WinAPI function from being called. Content wise there's no gain in using scrollbars - they just conveniently remember what you already scrolled.