请问IHTMLElement 的引用空间是什么？
为什么我下面这段代码 会提示，IHTMLElement 缺少引用空间。
  /// <summary>
  /// 得到元素的位置
  /// </summary>
  /// <param name="elem">元素</param>
  /// <returns></returns>
  public static Rectangle GetElementRect(IHTMLElement body, IHTMLElement elem)
  {
  int x, y, w, h;
  x = y = w = h = 0;

  // 计算元素本身的位置
  IHTMLElement2 elem2 = elem as IHTMLElement2;
  IHTMLRect elemRect = elem2.getBoundingClientRect();
  x = elemRect.left;
  y = elemRect.top;
  w = elemRect.right - elemRect.left;
  h = elemRect.bottom - elemRect.top;

  // TODO: 计算顶端htmlElem(docElem)的位置，一般不用计算，其位置应该为（0,0，xx，xx）

  // 计算父亲iframes
  if (body.document != elem.document)
  {
  List<IHTMLDOMNode> frames = new List<IHTMLDOMNode>();
  _getEleParentFrames(body as IHTMLDOMNode, elem as IHTMLDOMNode, frames);
  foreach (IHTMLDOMNode f in frames)
  {
  IHTMLElement2 frame2 = f as IHTMLElement2;
  IHTMLRect frameRect = frame2.getBoundingClientRect();
  x += frameRect.left;
  y += frameRect.top;
  }
  }

  Rectangle ret = new Rectangle();
  ret.X = x;
  ret.Y = y;
  ret.Width = w;
  ret.Height = h;

  return ret;
  }

------解决方案--------------------
在VS项目中添加Com对象引用：Microsoft Html Object Library

 using mshtml;

http://longkm.blog.163.com/blog/static/116662640201203033841286/