Delphi 5 使 DBGrid 支援滑鼠滾輪的程式碼

Delphi 5 的 TDBGrid 無法支援滑鼠滾輪移動資掉指標，而且當有 PickList 的 Column 或是 Lookup Field 下拉時
滾動滑鼠滾輪會有很奇怪的行為。
要解決這個問題，可以繼承 TDBGrid 寫一個新的 DBGrid 類別，並覆寫兩個方法：

interface
type
  TNewDBGrid = class(TDBGrid)
  protected
    function DoMouseWheelDown(Shift: TShiftState; MousePos: TPoint): Boolean; override;
    function DoMouseWheelUp(Shift: TShiftState; MousePos: TPoint): Boolean; override;    
  end;

implementation
  function TNewDBGrid.DoMouseWheelDown(Shift: TShiftState; MousePos: TPoint): Boolean;
  begin
    Result := False;
    if Assigned(OnMouseWheelDown) then
      OnMouseWheelDown(Self, Shift, MousePos, Result);
    if (not Result) and (DataLink <> nil) and (DataLink.Active)
       and (DataLink.DataSet <> nil) and (DataLink.DataSet.Active) then
    begin
      DataLink.DataSet.MoveBy(1);
      Result := True;
    end;
  end;

  function TNewDBGrid.DoMouseWheelUp(Shift: TShiftState; MousePos: TPoint): Boolean;
  begin
    Result := False;
    if Assigned(OnMouseWheelDown) then
      OnMouseWheelDown(Self, Shift, MousePos, Result);
    if (not Result) and (DataLink <> nil) and (DataLink.Active)
       and (DataLink.DataSet <> nil) and (DataLink.DataSet.Active) then
    begin
      DataLink.DataSet.MoveBy(-1);
      Result := True;
    end;
  end;