Thursday, October 18, 2007

ASP.NET compared to ASP classic

ASP.NET attempts to simplify developers' transition from Windows application development to web development by offering the ability to build pages composed of controls similar to a Windows user interface. A web control, such as a button or label, functions in very much the same way as its Windows counterpart: code can assign its properties and respond to its events. Controls know how to render themselves: whereas Windows controls draw themselves to the screen, web controls produce segments of HTML and JavaScript which form part of the resulting page sent to the end-user's browser. ASP.NET encourages the programmer to develop applications using an event-driven GUI paradigm (event-driven GUI model), rather than in conventional web-scripting environments like ASP and PHP. The framework attempts to combine existing technologies such as JavaScript with internal components like "ViewState" to bring persistent (inter-request) state to the inherently stateless web environment. Other differences compared to ASP classic are: Compiled code means applications run faster with more design-time errors trapped at the development stage. Significantly improved run-time error handling, making use of exception handling using try-catch blocks. Similar metaphors to Windows applications such as controls and events, which make development of rich user interfaces, previously only found on the desktop, possible. An extensive set of controls and class libraries allows the rapid building of applications, plus user-defined controls allow commonly used templates, such as menus. Layout of these controls on a page is easier because most of it can be done visually in most editors. ASP.NET leverages the multi-language capabilities of the .NET CLR, allowing web pages to be coded in VB.NET, C#, J#, etc. Ability to cache the whole page or just parts of it to improve performance. Ability to use the code-behind development model to separate business logic from presentation. If an ASP.NET application leaks memory, the ASP.NET runtime unloads the AppDomain hosting the erring application and reloads the application in a new AppDomain. Session state in ASP.NET can be saved in a SQL Server database or in a separate process running on the same machine as the web server or on a different machine. That way session values are not lost when the web server is reset or the ASP.NET worker process is recycled. Previous versions of ASP.NET (1.0 and 1.1) were criticized for their lack of standards compliance. The generated HTML and JavaScript sent to the client browser would not always validate against W3C/ECMA standards. In addition, the framework's browser detection feature sometimes incorrectly identified web browsers other than Microsoft's own Internet Explorer as "downlevel" and returned HTML/JavaScript to these clients with some of the features removed, or sometimes crippled or broken. However, in version 2.0, all controls generate valid HTML 4.0, XHTML 1.0 (the default) or XHTML 1.1 output, depending on the site configuration. Detection of standards-compliant web browsers is more robust and support for Cascading Style Sheets is more extensive. Web Server Controls: these are controls introduced by ASP.net for providing the UI for the web form. These controls are state managed controls and are WYSIWYG (What You See Is What You Get) controls.