Html Encode in ASP.NET Web Control

I have a file called TopicTree.ascx.cs which I am trying to output encoded strings like so:

            string subject = 开发者_如何学Creader.IsDBNull(0) ? string.Empty : reader.GetString(0);
            string topic = reader.IsDBNull(1) ? string.Empty : reader.GetString(1);

            subject = subject.Trim();
            topic = topic.Trim();

            string en_subject = Server.HtmlEncode(subject);
            string en_topic = Server.HtmlEncode(topic);

            string output = string.Format("<li><a href=\"searchresults.aspx?type=topics&subject={1}&topic={2}\" style=\"cursor: pointer;\">{0}</a></li>", topic, en_subject, en_topic);

But when I actually see the output on the screen, it isn't encoded. What's wrong?

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For the link URL, you want Server.UrlEncode() instead of Server.HtmlEncode().

But for the link display, you want Server.HtmlEncode(topic) on the topic as well.