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+2 A:

The <%=%> tags are simply a shortcut for Response.Write. If you think about it, the lambda expression is simply allowing you to defer execution of the Response.Write code until the appropriate time.

So, the important part is to call Response.Write to build your list, and when it’s time to inject the custom template, I just execute the lambda which does a Response.Write to inject the template.

Here is some example code to help illustrate:

public class TableBuilder
{
    private Action<int> _template;

    public TableBuilder Template(Action<int> template)
    {
        _template = template;
        return this;
    }

    public void Render()
    {
        var r = HttpContext.Current.Response;

        r.Write("<table>");

        for(int i=0; i<10; ++i)
        {
            r.Write("<tr><td>");
            if(_template != null)
            {
                _template(i);
            }
            r.Write("</td></tr>");
        }

        r.Write("</table>");
    }
}

Then, to use the Helper, do the following:

<body>
    <div>
    <% Html.TableBuilder().Template(i => { %>

                                          <%= i %>: I'm a template

                        <% }).Render(); %>
    </div>
</body>

This is a neat trick!

Page Brooks 2010-04-23 01:09:21

+1 for a great answer, even though I think the final syntax is uglier than string concatenation

Gabe Moothart 2010-04-27 17:58:27

I agree, it's pretty darn ugly!

Page Brooks 2010-04-28 02:11:47

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