Delphi 10中如何捕获TScrollBox的水平和垂直滚动位置（解决继承报错）

我编写的代码意图在用户拖动滚动条时获取TScrollBox的水平和垂直滚动条位置，但拖动后滚动条会重置回初始位置。我认为这是无法继承控件相关方法导致的。此前看过基于Lazarus实现该功能的视频，但现在需要在Delphi 10中完成开发。

表单代码（DFM） #

object Form1: TForm1
  Left = 0
  Top = 0
  Caption = 'Form1'
  ClientHeight = 299
  ClientWidth = 635
  Color = clBtnFace
  Font.Charset = DEFAULT_CHARSET
  Font.Color = clWindowText
  Font.Height = -11
  Font.Name = 'Tahoma'
  Font.Style = []
  OldCreateOrder = False
  Position = poScreenCenter
  PixelsPerInch = 96
  TextHeight = 13
  object ScrollBox1: TScrollBox
    Left = 8
    Top = 8
    Width = 434
    Height = 289
    TabOrder = 0
    object Panel1: TPanel
      Left = 48
      Top = 41
      Width = 443
      Height = 385
      Caption = 'Panel1'
      TabOrder = 0
    end
  end
  object lbScrollBox_Vertical_Pos: TLabeledEdit
    Left = 448
    Top = 24
    Width = 121
    Height = 21
    EditLabel.Width = 105
    EditLabel.Height = 13
    EditLabel.Caption = 'ScrollBox Vertical Pos:'
    TabOrder = 1
  end
  object lbScrollBox_Horizontal_Pos: TLabeledEdit
    Left = 448
    Top = 64
    Width = 121
    Height = 21
    EditLabel.Width = 118
    EditLabel.Height = 13
    EditLabel.Caption = 'ScrollBox Horizontal Pos:'
    TabOrder = 2
  end
end

单元代码（PAS） #

unit uMain;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Dialogs, Vcl.Imaging.pngimage, Vcl.ExtCtrls,
  Vcl.StdCtrls, Vcl.Forms;

type
  TScrollBox = class(Vcl.Forms.TScrollBox)
    procedure WMHScroll(var Message: TWMHScroll); message WM_HSCROLL;
    procedure WMVScroll(var Message: TWMVScroll); message WM_VSCROLL;
  end;

  TForm1 = class(TForm)
    ScrollBox1: TScrollBox;
    lbScrollBox_Vertical_Pos: TLabeledEdit;
    lbScrollBox_Horizontal_Pos: TLabeledEdit;
    Panel1: TPanel;
    procedure WMHScroll(var Message: TWMHScroll);
    procedure WMVScroll(var Message: TWMVScroll);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

{ TScrollBox }
{$REGION 'TScrollBox'}
procedure TScrollBox.WMHScroll(var Message: TWMHScroll);
begin
  inherited WMHScroll(Message);
  Form1.WMHScroll(Message);
end;

procedure TScrollBox.WMVScroll(var Message: TWMVScroll);
begin
  inherited WMVScroll(Message);
  Form1.WMVScroll(Message);
end;
{$ENDREGION 'TScrollBox'}

{ TForm1 }

{$REGION 'TForm1'}
procedure TForm1.WMHScroll(var Message: TWMHScroll);
begin
  lbScrollBox_Horizontal_Pos.Text := Message.Pos.ToString;
end;

procedure TForm1.WMVScroll(var Message: TWMVScroll);
begin
  lbScrollBox_Vertical_Pos.Text := Message.Pos.ToString;
end;
{$ENDREGION 'TForm1'}
end.

遇到的问题 #

尝试调用inherited WMHScroll(Message)时，编译器报错：

Cannot access a private symbol TScrollingWinControl.WMHScroll

原因是Vcl.Forms中的TScrollingWinControl类将WMHScroll方法声明为Private，无法直接继承调用。

内容的提问来源于stack exchange，提问作者Yuppski