ASP.NET Fundamentals: ASP.NET is Object-Oriented Language
ASP provides a relatively feeble object model. It provides a small set of objects; these objects are really just a thin layer over the raw details of HTTP and HTML. On the other hand, ASP.NET is truly object oriented. Not only does your code have full access to all objects in the .NET Framework, but you can also exploit all the conventions of an OOP (object-oriented programming) environment. For example, you can create reusable classes, standardize code with interfaces, extend existing classes with inheritance, and bundle useful functionality in a distributable, compiled component.
One of the best examples of object-oriented thinking in ASP.NET is found in server-based controls. Server-based controls are the epitome of encapsulation. Developers can manipulate control objects programmatically using code to customize their appearance, provide data to display, and even react to events. The low-level HTML markup that these controls render is hidden away behind the scenes. Instead of forcing the developer to write raw HTML manually, the control objects render themselves to HTML just before the web server sends the page to the client. In this way, ASP.NET offers server controls as a way to abstract the low-level details of HTML and HTTP programming.
Here’s a quick example with a standard HTML text box that you can define in an ASP.NET web page:
<input type="text" id="myText" runat="server" />
With the addition of the runat="server" attribute, this static piece of HTML becomes a fully functional server-side control that you can manipulate in C# code. You can now work with events that it generates, set attributes, and bind it to a data source. For example, you can set the text of this box when the page first loads using the following C# code:
void Page_Load(object sender, EventArgs e)
myText.Value = "Hello World!";
Technically, this code sets the Value property of an HtmlInputText object. The end result is that a string of text appears in a text box on the HTML page that’s rendered and sent to the client.
HTML Controls VS. Web Controls
When ASP.NET was first created, two schools of thought existed. Some ASP.NET developers were most interested in server-side controls that matched the existing set of HTML controls exactly. This approach allows you to create ASP.NET web-page interfaces in dedicated HTML editors, and it provides a quick migration path for existing ASP pages. However, another set of ASP.NET developers saw the promise of something more—rich server-side controls that didn’t just emulate individual HTML tags. These controls might render their interface from dozens of distinct HTML elements while still providing a simple objectbased interface to the programmer. Using this model, developers could work with programmable menus, calendars, data lists, validators, and so on.
After some deliberation, Microsoft decided to provide both models. You’ve already seen an example of HTML server controls, which map directly to the basic set of HTML tags. Along with these are ASP.NET web controls, which provide a higher level of abstraction and more functionality. In most cases, you’ll use HTML server-side controls for backward compatibility and quick migration, and use web controls for new projects.
ASP.NET web control tags always start with the prefix asp: followed by the class name. For example, the following snippet creates a text box and a check box:
<asp:TextBox id="myASPText" Text="Hello ASP.NET TextBox" runat="server" />
<asp:CheckBox id="myASPCheck" Text="My CheckBox" runat="server" />
Again, you can interact with these controls in your code, as follows:
myASPText.Text = "New text";
myASPCheck.Text = "Check me!";
Notice that the Value property you saw with the HTML control has been replaced with a Text property. The HtmlInputText.Value property was named to match the underlying value attribute in the HTML <input> tag. However, web controls don’t place the same emphasis on correlating with HTML syntax, so the more descriptive property name Text is used instead.
The ASP.NET family of web controls includes complex rendered controls (such as the Calendar and TreeView), along with more streamlined controls (such as TextBox, Label, and Button), which map closely to existing HTML tags. In the latter case, the HTML server-side control and the ASP.NET web control variants provide similar functionality, although the web controls tend to expose a more standardized, streamlined interface. This makes the web controls easy to learn, and it also means they’re a natural fit for Windows developers moving to the world of the Web, because many of the property names are similar to the corresponding Windows controls.