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How to Create ASP Applications Without Writing ASP Code


In this article, Robert shows us how to create web applications written in VB, allowing the use of all the features of the VB compiler and debugger.

Author Info:
By: Robert Gelb
Rating: 5 stars5 stars5 stars5 stars5 stars / 38
February 23, 2003
TABLE OF CONTENTS:
  1. · How to Create ASP Applications Without Writing ASP Code
  2. · How it Works
  3. · Troubleshooting
  4. · Conclusion

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How to Create ASP Applications Without Writing ASP Code - How it Works
(Page 2 of 4 )

So, how does this work? Let us start with basic facts. You will need one VB project. You will need a separate class for each page. That sounds like a lot of work especially if you have a large site. However, these classes are fairly small with no properties, one method and only several functions. Moreover, the classes are similar to each other, so there is going to be a lot of cut & paste. You will also need one ASP file. As this is where the users first touch your web site, it is here where we start to code. Create a file called exec.asp and add lines below to it.

<%@ Language=VBScript %>
<%
dim oInstance, sClass, sProject

sClass = Request.QueryString("cls")
sProject = Request.QueryString("prj")

set oInstance = Server.CreateObject(sProject & "." & sClass)
oInstance.ProcessRequest
set oInstance = nothing
%>


From here on out, that is all ASP you will ever have to write. Say goodbye to it, spit on it, cuss at it and generally get all the anger out of your system before proceeding.

Let's analyse what this ASP script is doing. It expects two items in the QueryString collection: cls and prj. Then it puts them together to form a class string and attempts to create an object. So for instance, if you type in on the browser line:

http://www.mysite.com/exec.asp?prj=MyProject&cls=View

...the ASP file assumes that you have a COM DLL with a class string called MyProject.View.

Futher down, notice the line oInstance.ProcessRequest. The ASP file assumes that the created object has a Public method called ProcessRequest. So obviously all the processing will go on in ProcessRequest method.

So far, so good - we need to create a class for each page and there should be a standard Public method called ProcessRequest...easy enough.

You maybe wondering at this point - how exactly am I going to get access to the ASP intrinsic objects? Well, because our COM object is being created with Server.CreateObject instead of CreateObject, the intrinsic objects will be available (with a little bit of code) in their full glory.

Now create a new ActiveX DLL project. Call the project "MyProject". Call the class "View".

Add the following to the class (you will have to add this to every single class that will be created the ASP script).

Option Explicit
Private mobjContext As ASPTypeLibrary.ScriptingContext
Private Const conHTMLTokenPrefix = "{|"
Private Const conHTMLTokenSuffix = "|}"
Public Sub OnStartPage(objContext As ASPTypeLibrary.ScriptingContext)
  Set mobjContext = objContext
End Sub
Public Sub OnEndPage()
  Set mobjContext = Nothing
End Sub
Public Sub ProcessRequest()
  On Error GoTo errProcessRequest

  'Your code goes here
  '...

  exitPoint:
  'generic exit point
  Exit Sub
errProcessRequest:
  'write out the error to the browser
  Call mobjContext.Response.Write(Err.Description)
  GoTo exitPoint
End Sub


Let's analyze this piece of code. The way ASP's Server.CreateObject works is that it looks for OnStartPage and OnEndPage methods to pass in the ASP context object (intrinsic objects, in other words). Once ASP passes in the object context intrinsic objects (Request, Response, Server, Application, Session) are available under the mobjContext super object. For instance, to write out a line of code you would use the following in the ProcessRequest sub.

mobjContext.Response.Write "My Test Line"

Pretty cool, huh? Keep in mind, you can place breakpoints in your ActiveX DLL and use the full power of the Visual Basic debugger.

Now you are probably thinking, the great thing about ASP was that I could create HTML page in my favorite editor and then intersperse VBScript code into it. Do I have to write HTML out one line at a time using this approach? Absolutely not - it would defeat the whole purpose of Rapid Application Development. In fact, our approach is relatively easy to implement.

We can achieve this ease by use of HTML templates. Let me explain. Let's say we have a page that has to be populated by the list of employees. So our final HTML page would look like this:

<html>
 <body>
  <font size=5><b>Employee List</b></font>
  <br>
    <select size="5">
      <option>John</option>
      <option>Mary</option>
      <option>Sam</option>
      <option>Claudia</option>
    </select>
  </body>
</html>
Employee List


Obviously, we can't just send out a hard-wired list, as our employee list may change. So we then create a template. We replace the hardwired names with a tag, our engine will understand.

<html>
<body>
<h1>Employee List</h1>
<select>
  {|EMPLOYEE LIST|}
</select>
</body>
</html>


So in our code, we will get the list of employees from the database, read in this template, replace the EMPLOYEE LIST tag with our real employee list and send the text out using mobjContext.Response.Write method. Easy enough? But wait, there is more. You can wrap the whole process of reading templates and replacing tags into a reusable class (one is provided with the download).

So here is how the final draft of the ProcessRequest method will look like:

Public Sub ProcessRequest()
  Dim objTemplate As clsTemplateManager
  Dim strReturn As String

  '******************************************
  'normally this code should be encapsulated
  'in another object or module
  Dim oConn As New ADODB.Connection
  Dim oRs As New ADODB.RecordSet
  Dim sList As String

  'open a connection to an Access database
  oConn.Open Provider="Microsoft.Jet.OLEDB.3.51;;Data Source=" & _
    App.Path & "\Sample.mdb"
  'populate the recordset with the names
  oRs.Open "select * from tblNames", oConn

  'build an HTML list
  Do While Not oRs.EOF
     sList = sList & "<option value=" & oRs!ID & ">" & _
     oRs!Name & "</option>"

     oRs.MoveNext
   Loop
  Set oRs = Nothing
  Set oConn = Nothing
  '******************************************

  'Template Manager
  Set objTemplate = New clsTemplateManager
  With objTemplate
    'Add values and Tokens
    .TokenAdd sList, "EMPLOYEE LIST"

    'Set Template Name and Tokens
    .TemplatePath = App.Path & "\Templates" & "\SeeName.htm"
    .TokenPrefix = gconHTMLTokenPrefix
    .TokenSuffix = gconHTMLTokenSuffix

    'Combine tokens and template and return HTML page
    strReturn = .WriteResponse
  End With

  ' Write out the page
  Call mobjContext.Response.Write(strReturn)

  exitPoint:
  'generic exit point
  Exit Sub
errProcessRequest:
  'write out the error to the browser
  Call mobjContext.Response.Write(Err.Description)
  GoTo exitPoint
End Sub


Here is a quick explanation on how to get this setup working on your computer.
  1. Make sure you have IIS or PWS installed and working.
  2. Then under c:\inetpub\wwwroot folder create a new directory called Sample. Unzip the downloaded project into this directory. Double-click on the MyProject.vbp file and click Run.
  3. Open your favorite browser and go to http://localhost/Sample
  4. That's all there is to it. Now you can place breakpoints in your VB code, learn how the code works and debug at will. The templates are location in the \Sample\Templates folder.
  5. What does the downloaded program do? Included with the download there is a simple access database With a single table. This table contains a list of employees. This application lets you manipulate the names of employees.

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