procedure TForm1.CreateExcel(NewInstance: boolean);
var IU: IUnknown;
    isCreate: boolean;
begin
  // FIXLSApp - private-поле у формы
  //            у меня в привычке добавлять букву I для всех интерфейсов
  //            понятно почему FI… ?
  if not Assigned(FIXLSApp) then begin // а зачем создавать, если уже есть?
    isCreate := NewInstance or
      (not SUCCEEDED( GetActiveObject(CLASS_Application_, nil, IU) ) );
    if isCreate then
      FIXLSApp := CreateComObject(CLASS_Application_) as _Application
    else
      FIXLSApp := IU as _Application;
  end;
end;

procedure TForm1.CreateExcel(NewInstance: boolean);
begin
  if not Assigned(IXLSApp) then begin
    FIXLSApp := TExcelApplication.Create(Self);
    if NewInstance then FIXLSApp.ConnectKind := ckNewInstance;
    FIXLSApp.Connect;
  end;
end;

procedure TForm1.ShowExcel;
begin
  if Assigned(FIXLSApp) then begin // а если он не создан?
    FIXLSApp.Visible[0] := true;
    if FIXLSApp.WindowState[0] = TOLEEnum(xlMinimized) then
      FIXLSApp.WindowState[0] := TOLEEnum(xlNormal);
    FIXLSApp.ScreenUpdating[0] := true;
  end;
end;

procedure TForm1.HideExcel;
begin
  if Assigned(FIXLSApp) then begin
    FIXLSApp.Visible[0] := false;
  end;
end;

procedure TForm1.ReleaseExcel;
begin
  if Assigned(FIXLSApp) then begin
    if (FIXLSApp.Workbooks.Count > 0) and (not FIXLSApp.Visible[0]) then begin
      FIXLSApp.WindowState[0] := TOLEEnum(xlMinimized);
      FIXLSApp.Visible[0] := true;
      Application.BringToFront;
    end;
  end;
  FIXLSApp := nil;
end;

procedure TForm1.ReleaseExcel;
begin
  if Assigned(IXLSApp) then begin
    if (IXLSApp.Workbooks.Count > 0) and (not IXLSApp.Visible[0]) then begin
      IXLSApp.WindowState[0] := TOLEEnum(xlMinimized);
      IXLSApp.Visible[0] := true;
      if not(csDestroying in ComponentState) then Self.SetFocus;
      Application.BringToFront;
    end;
  end;
  FreeAndNil(FIXLSApp);
end;

function TForm1.AddWorkbook(const WorkbookName: string): Excel8TLB._Workbook;
begin
  Result := nil;
  if Assigned(FIXLSApp) and (trim(WorkbookName) <> '') then begin
    Result := FIXLSApp.Workbooks.Add(WorkbookName, 0);
  end;
end;

procedure TForm1.btnDataToBookClick(Sender: TObject);
var LaunchDir: string;
    IWorkbook: Excel8TLB._Workbook;
    ISheet: Excel8TLB._Worksheet;
    IRange: Excel8TLB.Range;
    NewValueArray, V: OLEVariant;
    i: integer;
begin
  if Assigned(IXLSApp) then begin
    LaunchDir := ExtractFilePath( ParamStr(0) );
    IWorkbook := AddWorkbook( LaunchDir + 'Test.xls' );
    try
      ISheet := IWorkbook.Worksheets.Item['Лист1'] as Excel8TLB._Worksheet;
      IRange := ISheet.Range['TestRange', EmptyParam];
      NewValueArray := VarArrayCreate([0, 20, 1, 4], varVariant);
      for i := 0 to 20 do begin
        NewValueArray[i, 1] := TestDataArray[i].V1;
        NewValueArray[i, 2] := TestDataArray[i].V2;
        NewValueArray[i, 3] := TestDataArray[i].V3;
        NewValueArray[i, 4] := date + i;
      end;
      IRange.Value := NewValueArray;
    finally
      IRange := nil;
      ISheet := nil;
      IWorkbook := nil;
    end;
  end;
end;

procedure TForm1.btnDataClick(Sender: TObject);
type
var LaunchDir: string;
    IWorkbook: Excel97.ExcelWorkbook;
    ISheet: Excel97.ExcelWorksheet;
    IRange: Excel97.Range;
    NewValueArray, V: OLEVariant;
    i: integer;
begin
  if Assigned(IXLSApp) then begin
    LaunchDir := ExtractFilePath( ParamStr(0) );
    IWorkbook := AddWorkbook( LaunchDir + 'Test.xls' );
    try
      ISheet := IWorkbook.Worksheets.Item['Лист1'] as Excel97.ExcelWorksheet;
      IRange := ISheet.Range['TestRange', EmptyParam];
      NewValueArray := VarArrayCreate([0, 20, 1, 4], varVariant);
      for i := 0 to 20 do begin
        NewValueArray[i, 1] := TestDataArray[i].V1;
        NewValueArray[i, 2] := TestDataArray[i].V2;
        NewValueArray[i, 3] := TestDataArray[i].V3;
        NewValueArray[i, 4] := date + i;
      end;
      IRange.Value := NewValueArray;
    finally
      IRange := nil;
      ISheet := nil;
      IWorkbook := nil;
    end;
  end;
end;