ASP / .ASP (Active Server Pages)
ASP.NET is a web application framework marketed by Microsoft that programmers can use to build dynamic web sites, web applications and XML web services. It is part of Microsoft’s .NET platform and is the successor to Microsoft’s Active Server Pages (ASP) technology. ASP.NET is built on the Common Language Runtime, allowing programmers to write ASP.NET code using any Microsoft .NET language.
ASPX file format
ASPX is a text file format used to create Web form pages; in programming jargon, the ASPX file typically contains static HTML or XHTML markup, as well as markup defining Web Controls and Web User Controls where the developers place all the required static and dynamic content for the web page. Additionally, dynamic code which runs on the server can be placed in a page within a block <% — dynamic code — %> which is similar to other web development technologies such as PHP, JSP, and ASP, but this practice is generally frowned upon by Microsoft except for the purposes of data binding since it requires more calls when rendering the page.
The method recommended by Microsoft for dealing with dynamic program code is to use the code-behind model, which places this code in a separate file or in a specially designated script tag. Code-behind files are typically named something to the effect of MyPage.aspx.cs or MyPage.aspx.vb based on the ASPX file name (this practice is automatic in Microsoft Visual Studio and other IDEs). When using this style of programming, the developer writes code to respond to different events, like the page being loaded, or a control being clicked, rather than a procedural walk through the document.
ASP.NET uses a visited composites rendering technique. During compilation the template (.aspx) file is compiled into initialization code which will build a control tree (the composite) representing the original (static) template. Literal text goes into instances of the Literal control class, server controls are represented by instances of a specific control class. The initialization code is combined with user-written code (usually by the assembly of multiple partial classes) and results in a class specific for the page. The page doubles as the root of the control tree.
Actual requests for the page are processed through a number of steps. First, during the initialization steps, an instance of the page class is created and the initialization code is executed. This produces the initial control tree which is now typically manipulated by the methods of the page in the following steps. As each node in the tree is a control represented as an instance of a class, the code may change the tree structure as well as manipulate the properties/methods of the individual nodes. Finally, during the rendering step a visitor is used to visit every node in the tree, asking each node to render itself using the methods of the visitor. The resulting HTML code is sent to the client.
After the request has been processed, the instance of the page class is discarded and with it the entire control tree.
