ParseControl during runtime with a custom control

Introduction

ASP.NET 2.0 has made the use of master/details page inheritance much easier. It has, however, introduced some extra points to keep in mind while working with master/details pages. The ParseControl method is probably not the most difficult method to use, but if you want to render a custom control that is not part of the .NET framework, then you have to keep in mind to register the control on the page during runtime before rendering the control itself.

Background

I was recently trying to split web page content from the actual web page design. This led me to save the content in a database and have the page layout in a master/details page structure. To make life easier, I created custom controls with the additional functionality that was needed on the separate pages.

I did, however, get stuck while trying to render the controls during runtime. Even though I registered the custom controls in the master and details pages during design time, I kept getting a server error: "Unknown server tag...".

The solution is simple, if you know what you are looking for...

Using the Code

As I was working with master/details pages, I first had to get a reference to the ContentPlaceHolder of the master page during runtime from the details page:

Dim PlaceHolder1 As ContentPlaceHolder = Master.FindControl("ContentPlaceHolder1")

Next, declare a control of type Control and call the ParseControl method to assign the value of the custom control to the newly created control:

Dim c As Control
c = ParseControl("<search:searchbox ID="Searchbox" runat="server" />")

Add the newly created control to the ContentPlaceHolder control:

PlaceHolder1.Controls.Add(c)

As I mentioned at the beginning of the article, you first have to register the control on the page before you add the control.

Amend the ParseControl statement and add the @register directive that references your custom control.

c = ParseControl("<%@ register tagprefix="search" tagname="searchbox" " & _
   "src="~/searchresults.ascx" %><search:searchbox ID="Searchbox" runat="server" />")

Points of Interest

ParseControl accepts any HTML that you throw at it. You can therefore save the entire page's HTML in a database field and render it during runtime by parsing it out.