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There are two kinds of programming.
Programming with reusable code and non reusable code. To achieve
reusable code you can write functions and procedures. In ASP scripts
you can write functions and procedures and call them as often you
want. But the main drawback with ASP script is you can not hide
your code from the buyer. This is applicable when you are writing
some commercial applications and sell it. Your buyer can tweak the
code and even resell it as it is his own. When you want to avoid
this, here comes the concept of VB COM.
ActiveX DLLs:
ActiveX DLLs are COMponents where you can
hide your code,call it in your ASP and distribute with your application.
In this article we shall discuss how to write functions in ActiveX
Dlls and then call those same functions from ASP Scripts. We can
write Dlls with C++, VC++, Delphi and Visual Basic. Here we can
discuss How to with VB?
DLL's with VB
We
shall begin creating the DLL in Visual Basic. As an example we will
create a simple calculator that can do addition, division, subtraction
and multiplication with two numbers together. When we create the
project we are asked to choose the type of program we are creating.
Here we should select ActiveX DLL.
Initial Settings
1.
Let us change the project name first. Go to the the menu, choose
Project and then Project1 Properties. Under the ProjectName box
enter the name you want to call this object we are creating. I have
changed as SimpleCalculator as the Project name.
2. Leave the Threading model as "Apartment Threaded"
3. Adding the reference Library.
Now let us add the reference Library. Open the Project -> Preferences,
then select Active server Pages Object Library from the List of References
appearing.
4. Change the names of the Class1 module. In the properties box, normally
on the right hand side of the screen, change the (name) to something
pertinent. We shall name this "AddNumbers". We have now
set up the foundation for the DLL.
Likewise
let us create the other classes with the names "MulNumbers,SubNumbers
and DivNumbers".
Coding
Now
let us to code the SimpleCalculator DLL. The first thing that we
need to do is declaring the variables. We will place the following
lines into our AddNumbers class:
Public
Number1 As Variant
Public Number2 As Variant
We will now create the function that adds
these two variables. We will call this function Add. The function
Add will get the two variables which will be added and then passed
back as the addition result.
Function
Add(Number1, Number2)
Add = Number1 + Number2
End Function
Likewise
let us create the functions Subtract, Multiple and Divide and the
corresponding code lines. You know how to do that.
Compiling the
code
Compiling the code will produce the DLL.
From the File menu choose "Make SimpleCalculator.dll",
this will produce the SimpleCalculator.dll. Save the DLL in a directory
which you have chosen. If you have already saved the project or
compiled the DLL it will save it by default in that directory.
Now
we have created the created our first ActiveX DLL. Now we need to
set up our webpage to send and receive the information to the DLL
and display the results.
Registering the DLL
We will need to be running this on an IIS Server version 4.0 or later version. Means we need the platforms Windows NT 4.0, 2000, or XP First, copy the SimpleCalculator.dll to the server where the website will reside. Next, open a MS-DOS command line window on the server. When the command line window appears change the directory where you saved the dll. In my server I have saved the file under D:/dllDemo. Move to that directory now, then type the following
D:/dllDemo/regsvr32 SimpleCalculator.dll
This will register the DLL for use of the server. What happens is, the dll will be registered in your system Registry and that can be called by your ASP script which is running on the same server. If you are courageous enough to open and check your registry you will be able to find it. |
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Creating the webpage
Open your HTML editor and type the following
lines.
<HTML
<TITLE>Simple Calculator Test</TITLE>
<BODY>
<%
Dim AddResult,SubResult,MulResult,DivResult
Dim AddNum,SubNum,MulNum,DivNum
Set
AddNum=Server.CreateObject("SimpleCalculator.Addnumbers")
This
line of code will create the object which will allow us to interact
with our dll "SimpleCalculator". It references the class
object "AddNumbers".
Result=AddNum.Add(140774,51174)
Our variable, final answer will be equal
to the results of the function "additionfunction" in the
class "AddNumbers" in the dll "SimpleCalcuator".
We are passing the numbers 140774 and 51174 to be added.
Like
wise we can add the other lines of code,
Set
SubNum = Server.CreateObject("SimpleCalculator.SubNumbers")
Set MulNum = Server.CreateObject("SimpleCalculator.MulNumbers")
Set DivNum = Server.CreateObject("SimpleCalculator.DivNumbers")
SubResult
= SubNum.Add(140774,51174)
MulResult = DivNum.Add(140774,51174)
DivResult = MulNum.Add(140774,51174)
Response.write
AddResult & "<br>"
Response.write SubResult & "<br>"
Response.write MulResult & "<br>"
Response.write DivResult
%>
<BODY>
<HTML>
Now you can under stand the syntax of calling a dlls as
Set
objName = Server.CreateObject("ProjectName.ClassModuleName")
Call
the function name by passing the necessary variables.
OK.
You have done it, Congrats. Now you may think why you need a dll
and hence the object in your coding life? Let us see as a conclusion.
1.
You can reuse your code, as you have created your code as an Object.
2. Its fast in execution, as its already compiled.
3. You can hide your code, when you create code as a commercial
product.
4. You can always use it in your other programs and applications
in later developments.
5. Finally, Its challenging and intersting. Huh? |
