How to track scrolling of TScrollBox in Delphi - delphi

Question

Is there any simple way to track scrolling of TScrollbox content with his scrollbars ?
I have several TScrollBox components (each of them has some components inside) and would like to keep them synchronous. If one of scrollboxes scrolled (vertically or horizontally) i need to scroll other scrollboxes synchronously. That is why i need to know when scrollbars positions are changed.
It is strange, but Delphi's TScrollbox component doesn't have such events.

Answer 1

This can be done by adding own Events for the messages WM_HSCROLL and WM_HSCROLL.
The example is using a interposer class, this could also be done creating by an own component.
If you don't need two Events, you also can implement only one, beeing called in both message procedures.
unit Unit3;
interface
uses
Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.ExtCtrls;
type
TScrollBox=Class(VCL.Forms.TScrollBox)
procedure WMHScroll(var Message: TWMHScroll); message WM_HSCROLL;
procedure WMVScroll(var Message: TWMVScroll); message WM_VSCROLL;
private
FOnScrollVert: TNotifyEvent;
FOnScrollHorz: TNotifyEvent;
public
Property OnScrollVert:TNotifyEvent read FOnScrollVert Write FonScrollVert;
Property OnScrollHorz:TNotifyEvent read FOnScrollHorz Write FonScrollHorz;
End;
TForm3 = class(TForm)
ScrollBox1: TScrollBox;
Panel1: TPanel;
Panel2: TPanel;
ScrollBox2: TScrollBox;
Panel3: TPanel;
Panel4: TPanel;
procedure FormCreate(Sender: TObject);
private
procedure MyScrollHorz(Sender: TObject);
procedure MyScrollVert(Sender: TObject);
end;
var
Form3: TForm3;
implementation
{$R *.dfm}
{ TScollBox }
procedure TScrollBox.WMHScroll(var Message: TWMHScroll);
begin
inherited;
if Assigned(FOnScrollHorz) then FOnScrollHorz(Self);
end;
procedure TScrollBox.WMVScroll(var Message: TWMVScroll);
begin
inherited;
if Assigned(FOnScrollVert) then FOnScrollVert(Self);
end;
procedure TForm3.MyScrollVert(Sender: TObject);
begin
Scrollbox2.VertScrollBar.Position := Scrollbox1.VertScrollBar.Position
end;
procedure TForm3.MyScrollHorz(Sender: TObject);
begin
Scrollbox2.HorzScrollBar.Position := Scrollbox1.HorzScrollBar.Position
end;
procedure TForm3.FormCreate(Sender: TObject);
begin
ScrollBox1.OnScrollVert := MyScrollVert;
ScrollBox1.OnScrollHorz := MyScrollHorz;
end;
end.