Codenotes for Asp.Net

Chapter 1 INTRODUCTION ASP.NET is Microsoft's new technology for developing web-based applications. The most significant feature of ASP.NET (formerly named ASP+) is that it allows you to develop web applications using the intuitive drag-and-drop methodology that made Visual Basic popular. Simply "paint" your application within an intuitive development environment, and it will look and behave identically when deployed on a client's browser. In addition to this noteworthy capability, ASP.NET boasts a number of improvements over the traditional Active Server Page (ASP) technology that you may be using today. These improvements, which we will examine throughout this book, are listed below. STRONGLY TYPED AND COMPILED LANGUAGES The languages used to write traditional ASP applications (VBScript and JScript) have two primary limitations. First, they are inherently typeless, meaning that they have no concept of variable types. For example, in VBScript all variables are implicitly Variantsthere is no way to declare a variable as a more specific Integer or String. Second, these languages are interpreted, meaning that ASP translates an application's source on a line-by-line basis. If the fiftieth line of the application contains a syntax error, ASP must process the first forty-nine lines before the error will be detected. With ASP.NET, applications are developed using strongly typed languages such as Visual Basic, C++, JScript.NET, or Microsoft's new language, C# (pronounced "C-sharp"). Furthermore, applications in ASP.NET are compiled, which means that the entire source file is quickly examined and converted into machine code before the application is executed. Compiled applications are not only significantly faster than their interpreted counterparts, they are also easier to debug since syntax errors can be caught at compile time (while you are developing), as opposed to runtime (when the application executes). SEPARATION OF CODE FROM CONTENT Another cumbersome aspect of ASP development is the interspersion of source code with HTML. Because ASP scripts contain both code and HTML, source files are often lengthy, difficult to read, and hard to debug. The intermixing of HTML with ASP code is particularly problematic for larger web applications, where content must be kept separate from business logic. ASP.NET eliminates this problem by keeping the design and programmatic aspects of your application separate. One file contains the application's design (the HTML), whereas another file, called the CodeBehind file, houses its associated logic (the source code). Thus, developers can work on the application's code while designers and graphic artists independently work on its content. BROWSER NEUTRALITY Supporting multiple browsers is a recurrent and persistent problem when developing web applications. ASP.NET eliminates this concern through its Web Control technology. A Web Control is a graphical entity very similar to an intrinsic control found in Visual Basic 6 (such as a Textbox or Button). Like its Visual Basic counterpart, a Web Control exposes a rich event model that you program against (such as a TextChanged() event, which triggers when the contents of the control change). What is important about Web Controls is that they reside entirely on the server and generate client-side and server-side code to render themselves appropriately in a browser. In the eyes of ASP.NET, a browser can be one of two types: An UpLevel browser, defined as Internet Explorer 4.0 or higher; or a DownLevel browser, defined as everything else (including all versions of Netscape). If the browser is UpLevel, then the control generates client-side JavaScript so that events can be trapped directly on the client. If the browser is of the DownLevel type, then the control generates standaBrill, Gregory is the author of 'Codenotes for Asp.Net', published 2002 under ISBN 9780812992205 and ISBN 0812992202.