Microsoft Visual Basic Custom Libraries

	Custom Libraries

Introduction

If you cannot find a function you want, you can create one and be able to use it. If you plan to use such a function over and over again in different programs, you can create a library and store the function in it. You can even create one or a series of commercial functions and be able to distribute or sell it through a library.

A library is a program that contains procedures and/or other resources that other programs can use. Such a program is created with the same approach as the programs we have created so far. Because a library is not an executable, it does not need the Main() procedure. A library usually has the extension .dll.

Creating a Library

A library can be made of a single file or as many files as necessary. A file that is part of a library can contain one or more procedures (or classes). Each procedure (or class) should implement a behavior that can eventually be useful and accessible to other procedures (or classes). The contents of a library are created exactly like those we have used so far. Everything depends on how you compile it.

To create a library:

On the main menu of Microsoft Visual Studio, you can click File -> New -> Project
On the Start Page, on the right side of Create, you can click Project
On the Standard toolbar, you can click the New Project button or click the arrow of the New Project button and click New Project

In the Templates list of the New Project dialog box, click Class Library. Accept or specify the name and click OK. Once the starting project has been generated, write the necessary code. To compile it, on the main menu, click Build -> Build Solution. If you were working from the command prompt, you would execute the following command:

vbc /target:library NameOfFile.vb

After doing this, a library with the name of the file and the extension .dll would be created. If you use the above technique, the new library would be created using the name of the file. If you are working from the Command Prompt, to compile the project and create a custom name, use the following syntax:

vbc /target:library /out:DesiredNameOfLibrary.dll NameOfFile.vb

Here is an example:

vbc /target:library /out:Arithmetic.dll exo.vb

Practical Learning: Creating a Library

Start Microsoft Visual Studio
To start a new project, on the main menu, click File -> New -> Project...
In the Project Types list, make sure Visual Basic is selected.
In the Templates List, click Class Library
Change the Name to Arithmetic and click OK
In the Solution Explorer, right-click Module.vb and click Rename
Type Operations.vb and press Enter

Change the file as follows:

Public Class Arithmetic
    Function Add(ByVal x As Double, ByVal y As Double) As Double
        Return x + y
    End Function

    Function Subtract(ByVal x As Double, ByVal y As Double) As Double
        Return x - y
    End Function

    Function Multiply(ByVal x As Double, ByVal y As Double) As Double
        Return x * y
    End Function

    Function Divide(ByVal x As Double, ByVal y As Double) As Double
        If y = 0 Then Return 0
        Return x / y
    End Function
End Class

To create the library, on the main menu, click Build -> Build Arithmetic
To start another project, on the main menu, click File -> New -> Project...
In the Templates List, click Console Application
Change the Name to Algebra and click OK
In Windows Explorer or My Documents, locate the Arithmetic folder that contains the library project. Access a sub-folder of the same name, followed by the bin sub-folder, and followed by the Debug sub-folder
Right-click Arithmetic.dll and click Copy
Still in Windows Explorer or My Documents, locate the Algebra folder that contains the current project. Right-click the sub-folder of the same name and click Paste
In the Solution Explorer, right-click Algebra and click Add Reference...
In the Add Reference dialog box, click the Browse tab
Use the Look In combo box to locate and select a sub-folder named Algebra in the current project
Click Arithmetic.dll and click OK
In the Solution Explorer, right-click Module1.vb and click Rename
Type Exercise.vb and press Enter. Accept to make all necessary changes

Change the the file as follows:

Imports Operations

Module Exercise

    Public Function Main() As Integer
        Dim Result As Double
        Dim Oper As Arithmetic
        Dim Number1 As Double, Number2 As Double

        Number1 = 244.58
        Number2 = 5082.88
        Oper = New Arithmetic
        Result = Oper.Add(Number1, Number2)

        MsgBox(Number1 & " + " & Number2 & " = " & Result)
        Return 0
    End Function

End Module

To execute the project, on the main menu, click Debug -> Start Without Debugging