ASP.NET Architecture, Part 2 - Creating User Controls
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ASP.NET divides the built-in server controls in two groups: HTML controls and web controls. Each is contained within its own namespace. HTML controls map one to one with standard HTML elements, whereas some elements do not map to a specific HTML control. You have the option of changing the functionality of a page at runtime by modifying the control’s attributes programmatically. Creating a user control is new to ASP.NET. User controls consist of HTML markup or ASP.NET code that bears the .ascx file extension. You can employ the @ Control directive to specify precisely how a control behaves on the web form. A caveat to employing user controls is that you cannot call them directly. They must reside on an already existing page. In addition, user controls should not contain <html>, <body>, or <form> elements primarily because they are already present on the page where your control is placed. You can strong type the control programmatically by adding the ClassName attribute as follows:
<%@ Control ClassName="RegisterClient" %>
Let’s create a user control and see how easy it is to do.
<%@ Control ClassName="RegisterClient" %>
<script language="vb" runat="server" %>
Private name As String = ""
Public Property Name As String
Get
Return name
End Get
Set
name = Value
End Set
End Property
Public Sub GreetClient()
Label1.Text = "Please register to use our services", & name
End Sub
</script>
<asp:Label id="Label1" runat="server"></asp:Label>
The file should be saved as Register.ascx and stored in your Internet Information Services virtual directory.
The code declares a string variable called name; then a property procedure called Name sets and retrieves the value of the variable. Finally, a Sub procedure called GreetClient() sets the Text property of the Label server control.
 This has been part two of ASP.NET Architecture (see part 1 here), chapter six of .NET & J2EE Interoperability, by Dwight Peltzer (McGraw-Hill/Osborne, ISBN 0-07-223054-1, 2004).
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