how does using HtmlHelper.BeginForm() work?

Question

Ok so I want to know how

<% using (Html.BeginForm()) { %>
  <input type="text" name="id"/>
<% } %>

produce

<form>
  <input type="text" name="id"/>
</form>

namely how does it add the </form> at the end? I looked in codeplex and didn't find it in the htmlhelper. There is a EndForm method, but how does the above know to call it?

The reason is I want to create an htmlhelper extension, but don't know how to close out on the end of a using.

Any help would be appreciated :)

Answer 1

BeginForm returns an IDisposable which calls EndForm in Dispose.

When you write using(Html.BeginForm()) { ... }, the compiler generates a finally block that calls Dispose, which in turn calls EndForm and closes the <form> tag.

You can duplicate this effect by writing your own class that implements IDisposable.