Visual Basic Scripts

VB NET

A Visual Basic program is a set of commands, coded in the special syntax of the language, that causes the computer to perform some type of processing to generate information where none has existed before. These commands, or statements, are arranged in a logical order so that the computer can carry out the processing in a step-by-step sequence. Within the context of Web-based processing, a set of Visual Basic statements is often called a script.

Visual Basic code can be physically located in two places. Code can appear on the Web page itself; it also can appear in a separate file that is accessible from the Web page. Wherever they appear, Visual Basic scripts are the processing routines called upon by the Web page to carry out its processing activities and to produce output results for display on the page.Script Blocks

When Visual Basic code appears on a Web page, it must be enclosed within an identifiable script block. A script block is simply a section of the page surrounded by <script> tags in the following format.

<script runat=”server” [language=”vb|Visual Basic”] >

Visual Basic code

</script>

 

The attribute runat=”server” indicates that the enclosed script is to be run, or executed, by the Web server computer prior to transmitting the page to the client computer which made the URL request for the page. The attribute also differentiates server scripts from browser scripts that also are enclosed within <script> tags. These browser-based scripts are usually written in the JavaScript language.

Optionally, language=”vb” or language=”Visual Basic” can be included in the opening tag to indicate the programming language used in the script. This attribute is optional since Visual Basic is the default server language for Web page scripts.

A script block can appear anywhere on the Web page, and there can be as many script blocks as needed. However, a single script block is normally sufficient, and it commonly appears at the top of the Web page, prior to any HTML code that appears on the page. The reason for placing the script at the top of the page is in recognition of the fact that the server runs the script first, before it takes action on any other components of the Web page.

Subprograms

A script block is the enclosing container for all Visual Basic statements on a page. However, most statements must be enclosed inside another programming structure in order to be executed properly. This structure is a named container that can be called upon to perform the processing given by its enclosed statements. The most common container for statements is a subprogram.

Although the topic of subprograms and other similar containers is covered later in these tutorials, one particular subprogram can provide the wrapper for the statements introduced over the next several tutorials. The Page_Load subprogram is the one that the server first runs when the Web page is opened. Any statements can be placed inside this subprogram for immediate execution. A general script setup to run Visual Basic statements, then, is shown by the following outline.

<script runat=”server”>

Sub Page_Load

Visual Basic statements

End Sub

</script>

As you are introduced to the foundational statements offered by the Visual Basic language over the next several tutorials, keep in mind that they can have residence within the above script block and its Page_Load subprogram.

Code-Behind Files

The second location for Visual Basic code is in a separate code-behind file. This file contains only Visual Basic code packaged as a Visual Basic class. The file name is given the extension .vb to indicate a Visual Basic program.

There are slight coding differences between an internal script and an external class. A Web-page script is supplied with various default language settings that must be made explicit when coding a formal Visual Basic class. These differences are pointed out later in the tutorials. When learning the Visual Basic language it is best to develop Web pages with on-page scripts to remove the complexities of constructing classes.

Resources: www. msconline.maconstate.edu

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