ASP.NET - Server Controls

Server controls are tags that can be understood by the server.

ASP Classic

The listing below was copied from the previous chapter.

The inline code in red (also called a render block) is executed by the server before the page is sent to a browser:

<html>
<body bgcolor="yellow">
<center>
<h2>Hello W3Schools!</h2>
<p><%Response.Write(now())%></p>
</center>
</body>
</html>

Click on this link dynpage.asp to display the HTML page.

The code above illustrates a limitation in Classic ASP: The render block has to be placed where you want the output to appear.

With Classic ASP it is impossible to separate executable code from the HTML itself. This makes the page difficult to read, and difficult to maintain.

ASP.NET - Server Controls

ASP.NET has solved the "spaghetti code" problem described above with something called server controls.

Server controls are tags that can be understood by the server.

There are three kinds of server controls:

HTML Server Controls - Traditional HTML tags
Web Server Controls - New ASP.NET tags
Validation Server Controls - allow you to validate input

ASP.NET - HTML Server Controls

HTML server controls are standard HTML tags, except for one thing: they contain a runat="server" attribute.

This code illustrates how ASP.NET makes it possible to separate the executable code from the rest of the HTML:

<%
TimeStamp.InnerText=now()
%>
<html>
<body bgcolor="yellow">
<center>
<h2>Hello W3Schools!</h2>
<p id="TimeStamp" runat="server"></p>
</center>
</body>
</html>

The runat="server" attribute in the example above, has turned the <p> tag into a server control. In addition the id attribute gives it a name to make it possible to reference it from executable code.

The executable code itself has been moved outside the HTML.

ASP.NET - Web Server Controls

Web server controls are similar to HTML server controls, but more complex. They don't "act" as a part of an existing HTML tag but have a more "independent" existence. Web controls are often used in interactive applications such as input forms.

Web server controls are tags starting with <asp:

This code illustrates the use of Web server controls:

<%
TimeStamp.Text=now()
%>
<html>
<body bgcolor="yellow">
<center>
<h2>Hello W3Schools!</h2>
<p><asp:label id="TimeStamp" runat="server" /></p>
</center>
</body>
</html>

Notice the Web server control called asp:label in the listing above. This is one of many predefined Web server controls that can be understood by ASP.NET.

Also notice the use of Text instead of InnerText to change the content of the tag. This is defined by the object model for this particular Web server control.

ASP.NET - Validation Server Controls

Validation server controls allow you to validate an input server control (like a TextBox), and display a message when validation fails.

Each validation control performs a specific type of validation (like validating against a specific value or a range of values).

By default, page validation is performed when a Button, ImageButton, or LinkButton control is clicked. You can prevent validation when a button control is clicked by setting the CausesValidation property to false.

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