DLL Tutorial: MyFirstDLL
Author: Rob Loach
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In this tutorial you will learn:
[if !supportLists]·
[endif]How to make a DLL file.
[if !supportLists]·
[endif]How to call the DLL from a different project.
[if !supportLists]·
[endif]How to make a class with properties, subs, and
functions.
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Welcome
Welcome to my tutorial,
MyFirstDLL. If you read through this
tutorial, and do all the coding, it will take you about 3-10 minutes for you to
fully understand how the DLL system in VB works. If you want to do it more quickly, all the important
information is bolded. The goal of
this tutorial is to explain step-by-step how to create and use a DLL file.
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What is a DLL?
A DLL is a file that you
can have your application use. A
programmer can use the functions in a DLL file, but the code itself cannot be
accessed. This allows you to make
various things such as game engines.
You can then distribute the engine to the public without actually giving
out the code. DLLs are very useful
because it allows you to hold a large amount of code in only one file.
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So how do I make a DLL file?
To make a DLL, follow
these simple steps:
[if !supportLists]1)
[endif]Open
Microsoft Visual Basic.
[if !supportLists]2)
[endif]Goto
File à
New Project.
[if !supportLists]3)
[endif]Start
an ActiveX DLL.
[if !supportLists]4)
[endif]This
new window is your DLL. You currently
only have one object in it, a class.
Now it is time to put in the code that you want your DLL to use. In this case, just add in the following
code.
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'=====================
'Title: MyFirstDLL
'Purpose: Holds a text string and when the DisplayMsg
' sub is called, it displays a message box
of
' the string.
' This is just an example showing how a
class
' file works.
Now you can type CLASS and . and
' a list of properties and subs will
appear.
'Author: Rob Loach
'=====================
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'Variables
'=========
Private
p_Text
As String
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'Properties
'==========
Public Property Get
Text() As String
Text =
p_Text
End Property
Public Property Let
Text(ByVal i_Text
As String)
p_Text
= i_Text
End Property
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'Functions and Subs
'==================
Public Sub DisplayMsg()
MsgBox
p_Text, vbOKOnly, "DLL Function Called"
End Sub
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This is your class file inside
your new DLL. All it will do is
hold a string called p_Text. Calling
the property named Text can change the string.
When the DisplayMsg sub is called, it will make a messagebox saying the
Text string.
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You could put any code you want
into this class. This is just an example
that we will be using. You can put
anything you want into the DLL file (Forms, Classes, Modules, etc).
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[if !supportLists]5)
[endif]Now
you have to rename your class file.
For this example, name it clsMyFirstDLL.
[if !supportLists]6)
[endif]You
can then rename your DLL to MyFirstDLL (or anything you want). Click on the ActiveX Icon in the top left of
the project window. Next, in the
properties window, change the Name property to MyFirstDLL.
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[endif]Now,
once your done making your DLL, your going to have to save it as an actual
file. Goto File à
Make MyFirstDLL.dll… Save it
wherever you want. Just take note of
where you put it.
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Now that I’ve made my DLL, how do I use it?
You can call the DLL a
number of ways. In this tutorial, I
will only show you one.
Once you have a DLL file,
and want to make use of it, do the following.
[if !supportLists]1)
[endif]Start
Microsoft Visual Basic.
[if !supportLists]2)
[endif]Start
a Standard EXE. This will be the new
project that will use the DLL.
[if !supportLists]3)
[endif] Goto Project à
References. It will take some time
to load. This is a list of DLL files
that the application is currently using.
Click on browse and load the DLL that you just made. It will then add the DLL to the list. Now click on OK. Your project has now successfully loaded the DLL information,
functions, and properties into memory.
[if !supportLists]4)
[endif]Now
is the time to use the DLL and see how the class works within the DLL. Make two command buttons, one named
Command1 and the other named Command2.
Next, make a textbox and name it Text1. These are going to be used in this example.
[if !supportLists]5)
[endif] Now view the code of the form and put in the
following code:
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'=====================================
'Title: MyFirstDLL Application Use
'Purpose: An application that uses the DLL that was just
made.
' It requires a form (Form1)
' two commands (Command1 and Command2)
' a text box (Text1).
'Author: Rob Loach
'=====================================
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'Variables
'=========
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'Make a variable that uses the class
in the
'MyFirstDLL DLL file so that we can
make use of it.
Dim MyFirstDLL As
New clsMyFirstDLL
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Private Sub Command1_Click() 'Set text
'Set the property of MyFirstDLL to text1 text
'This shows how to set a property of the class/DLL.
MyFirstDLL.Text = Text1.Text
End Sub
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Private Sub Command2_Click()
'Call the sub DisplayMsg in the DLL.
'This shows how to call a sub/function of the
class/DLL.
MyFirstDLL.DisplayMsg
End Sub
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Private Sub Form_Load()
'Initialize the Objects
Form1.Caption =
"MyFirstDLL"
Text1.Text = "Enter text to be displayed
here..."
Command1.Caption = "Set Text"
Command2.Caption = "Display Text"
End Sub
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[if !supportLists]6)
[endif]Now
run the program and play around with it.
As you can see, when you click Set Text, it sets the property “Text” in
MyFirstDLL to whatever you typed in. When
you click Display Text, it calls the sub DisplayMsg in the DLL.
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Quick Things To Remember
[if !supportLists]·
[endif]To make a DLL, use ActiveX DLL project.
[if !supportLists]·
[endif]Project à References
[if !supportLists]·
[endif]Keep your DLLs in the same directory as the project.
[if !supportLists]·
[endif]Name everything to keep organization.
[if !supportLists]·
[endif]Make sure to use as many variables as possible in every
sub/function in your DLLs to allow diversity of programs.
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Conclusion
That concludes this tutorial! In it you learned how to make a DLL and use it in a different
program. Thank you for reading MyFirstDLL
and I hope you have learned the DLL-VB concept.
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(4(4 Vote))