Visual Basic

Foundations: The Free Stuff

Assuming you've installed and set up your Web server, the next step is to fire up Visual Basic 6. Select New Project from the File menu to display the New Project dialog box, and then select the IIS Application template to start developing your new application.

Right away you'll notice something different-the Project Explorer window contains a folder called Designers in the project tree. Designers, which act as hosts for a particular type of object, appeared in Visual Basic 5, although none of the templates supplied with Visual Basic 5 used them. Designers could (and still can) be added to a project by selecting Components from the Project menu, choosing the Designers tab of the Components dialog box, and then checking a designer in the list. Designers have features that enable the development of particular objects within the Visual Basic integrated development environment (IDE). In Visual Basic 5, two designers came as standard components; now there are seven. IIS Applications use the WebClass designer to develop WebClass objects. Each IIS application contains at least one WebClass object.

The IIS Application template provides you with a single item in your new project; a WebClass object named WebClass1. Even at this early stage your project is in a state where it can be run (and can demonstrate the fact that it is running). Clicking the Start button on the toolbar (or using any of the other methods to start a project in the IDE) brings up a scaled-down version of the Project Properties dialog box with only the Debugging tab visible. This allows you to specify which WebClass component you want to start the application with in an IIS application. This dialog box also contains a Use Existing Browser check box, which, when selected, will launch the application in a browser that's currently running. If this option is not checked, Visual Basic will launch Internet Explorer 4 to act as the client for your application. Even if Internet Explorer 4 is not your default browser, Visual Basic will still launch Internet Explorer 4 (and then ask you if you want to make it your default browser). The options available when you start the project in the IDE are shown in Table 3-2.

Table 3-2 Project Debugging Options

Startup Option Possible Use
Wait For Components To Be Created Simulates a more normal method of operation, where the application is already running on a Web server and waits for browser requests
Start Component Opens browser and automatically accesses the specified component
Start Program Accesses the application using a different browser or a program with browsing capabilities
Start Browser With URL Accesses a particular part of your application or a page with a link to your application

Once you have chosen your preferred options from this dialog box, you will be prompted to save your project and its files. In an IIS application the directory where you save your project has a bit more significance than normal since this is where the temporary files created at run/debug time will be placed. It is also the same directory where the HTML template files used in the application will be stored. When your application is deployed on a Web server, the directory structure used for development will be mirrored in the production directories, the only change being to the root directory for the application. As far as IIS is concerned, all directories stemming from a virtual root directory are part of the same Web application, unless they themselves are the virtual root directory for another application.

Once you've saved your project files, you'll be prompted for the name of a virtual directory that the Web server should use to host this application during development. When you deploy your application on your production Web server, you'll be able to specify into which directory you want to place your application files. You'll also be able to specify which virtual directory you want your Web server to associate with the physical application directory. The virtual directory name will form part of the URL that browsers use to reference your application.

Finally, after selecting a name for the virtual directory, your application will start. To see your application running, you'll have to switch to a Web browser. If you've chosen to start with a particular Web class, the focus will automatically have been transferred to a browser. If you have not yet entered any code, you'll be greeted by a Web page with the heading "WebClass1's Starting Page."

It's worth taking a moment to have a look in the project directory for the application. In addition to seeing the Web class designer files and project files, you'll also see that an ASP file has been created. During development, this is a temporary file that gets created whenever you start a debug session for your application and is destroyed when you finish the debug session. If you examine this file in Notepad, you'll see that this ASP file (WEBCLASS1.ASP for the default project) contains the following code:

  If (VarType(Application("~WC~WebClassManager")) = 0) Then
      If (VarType(Application("~WC~WebClassManager")) = 0) Then
          Set Application("~WC~WebClassManager") = _
      End If
  End If
  Application("~WC~WebClassManager").ProcessNoStateWebClass _
      "Project1.WebClass1", _
      Server, _
      Application, _
      Session, _
      Request, _

This is an ASP script (as shown by the script delimiters <% and %>) that uses the ASP Server and Response objects and creates an instance of our Web class. From this script, we can see that our IIS application is a single-page ASP application that simply runs an instance of a single object. Normally, as already mentioned, an ASP application would be made up of ASP files containing a mixture of script code to be processed by the Web server and HTML to be returned to the browser.

If we now shut down the browser and return to Visual Basic, we see that the application is still running. The temporary ASP used to access our application is still in existence, so we can start the browser and run the application again. We can even connect to our application from another computer if the Web server has been set up to allow access from that computer. You must close down your application from within Visual Basic, which causes the temporary ASP file to be deleted and thus denies access to your application.

So that's the Web application equivalent of "Hello World" done without writing even a single line of code! (As far as "Hello World" applications go, a Web application is likely to greet more of the world than a C application or a Visual Basic application.)

by BrainBellupdated