Walkthrough: Defining Classes (Visual Basic)
This walkthrough demonstrates how to define classes, which you can then use to create objects. It also shows you how to add properties and methods to the new class, and demonstrates how to initialize an object.
Your computer might show different names or locations for some of the Visual Studio user interface elements in the following instructions. The Visual Studio edition that you have and the settings that you use determine these elements. For more information, see Personalizing the IDE.
To define a class
Create a project by clicking New Project on the File menu. The New Project dialog box appears.
Select Windows Application from the list of Visual Basic project templates to display the new project.
Add a new class to the project by clicking Add Class on the Project menu. The Add New Item dialog box appears.
Select the Class template.
Name the new class
UserNameInfo.vb, and then click Add to display the code for the new class.
Public Class UserNameInfo End Class
You can use the Visual Basic Code Editor to add a class to your startup form by typing the
Classkeyword followed by the name of the new class. The Code Editor provides a corresponding
End Classstatement for you.
Define a private field for the class by adding the following code between the
Private userNameValue As String
Declaring the field as
Privatemeans it can be used only within the class. You can make fields available from outside a class by using access modifiers such as
Publicthat provide more access. For more information, see Access levels in Visual Basic.
Define a property for the class by adding the following code:
Public Property UserName() As String Get ' Gets the property value. Return userNameValue End Get Set(ByVal Value As String) ' Sets the property value. userNameValue = Value End Set End Property
Define a method for the class by adding the following code:
Public Sub Capitalize() ' Capitalize the value of the property. userNameValue = UCase(userNameValue) End Sub
Define a parameterized constructor for the new class by adding a procedure named
Public Sub New(ByVal UserName As String) ' Set the property value. Me.UserName = UserName End Sub
Sub Newconstructor is called automatically when an object based on this class is created. This constructor sets the value of the field that holds the user name.
To create a button to test the class
Change the startup form to design mode by right-clicking its name in Solution Explorer and then clicking View Designer. By default, the startup form for Windows Application projects is named Form1.vb. The main form will then appear.
Add a button to the main form and double-click it to display the code for the
Button1_Clickevent handler. Add the following code to call the test procedure:
' Create an instance of the class. Dim user As New UserNameInfo("Moore, Bobby") ' Capitalize the value of the property. user.Capitalize() ' Display the value of the property. MsgBox("The original UserName is: " & user.UserName) ' Change the value of the property. user.UserName = "Worden, Joe" ' Redisplay the value of the property. MsgBox("The new UserName is: " & user.UserName)
To run your application
Run your application by pressing F5. Click the button on the form to call the test procedure. It displays a message stating that the original
UserNameis "MOORE, BOBBY", because the procedure called the
Capitalizemethod of the object.
Click OK to dismiss the message box. The
Button1 Clickprocedure changes the value of the
UserNameproperty and displays a message stating that the new value of
UserNameis "Worden, Joe".