C# WebBrowser 获得选中部分的html源码

Winform程序  2.0的. 需要引用Microsoft.mshtml.

         private  void Form1_Load( object sender, EventArgs e)
        {
            webBrowser1.Navigate( " http://www.baidu.com ");
            webBrowser1.DocumentCompleted +=  new WebBrowserDocumentCompletedEventHandler(webBrowser1_DocumentCompleted);
        }

         void webBrowser1_DocumentCompleted( object sender, WebBrowserDocumentCompletedEventArgs e)
        {
            webBrowser1.Document.MouseUp +=  new HtmlElementEventHandler(Document_MouseUp);
        }

         void Document_MouseUp( object sender, HtmlElementEventArgs e)
        {
            IHTMLDocument2 document = (IHTMLDocument2)webBrowser1.Document.DomDocument;
            IHTMLTxtRange htmlElem = (IHTMLTxtRange)document.selection.createRange();
             string s = htmlElem.htmlText;
            richTextBox1.Text = s;
        }