Chapter 11: Object-Oriented Programming

    Classes and Objects
    Fields, Properties, Methods, and Events
    Class vs. Object Members
    Abstraction, Encapsulation, Inheritance, and Polymorphism
    Overloading, Overriding, and Shadowing
    Constructors and Destructors
    An OOP Example
    Structures and Modules
    Immediate Solutions: Creating Classes
    Creating Objects
    Creating Structures
    Creating Modules
    Creating Constructors
    Using Is to Compare Objects
    Creating Data Members
    Creating Class (Shared) Data Members
    Creating Methods
    Creating Class (Shared) Methods
    Creating Properties
    Creating Class (Shared) Properties
    Creating Events
    Creating Class (Shared) Events
    Overloading Methods and Properties
    Getting Rid of Objects When You're Done with Them
    Triggering Garbage Collection
    Creating Class Libraries
    Creating Namespaces
    Using the Finalize Method (Creating Destructors)

In Depth

Just about everything you do in Visual Basic .NET involves objects in some way—even simple variables are based on the Visual Basic Object class. And all your code has to appear in a class of some sort, even if you're using a module or structure, which are also types of classes now. For these reasons, it's important to understand object-oriented programming (OOP) in Visual Basic, and now more than ever before. This and the following chapter are dedicated to OOP.

We haven't looked at OOP in detail until now, because we didn't really need to understand a great deal of the programming aspect of it. Visual Basic comes with thousands of built-in classes, ready to use, so we didn't have to plumb the depths too much. We knew that Windows forms are classes, of course, based on the System.Windows.Forms.Form class, and that our code was part of that class:

Public Class Form1
    Inherits System.Windows.Forms.Form

    Private Sub Form1_Load(ByVal sender As System.Object, _
    ByVal e As System.EventArgs) Handles MyBase.Load
        ⋮
    End Sub

End Class

And we knew, too, that controls such as text boxes are really based on classes, as with the TextBox class, as in this example from Chapter 5, CreateTextBox, where we created a new object of that class and used that object's various members to configure it:

    Private Sub Button1_Click(ByVal sender As System.Object, _
        ByVal e As System.EventArgs) Handles Button1.Click
        Dim TextBox1 As New TextBox()
        TextBox1.Size = New Size(150, 20)
        TextBox1.Location = New Point(80, 20)
        TextBox1.Text = "Hello from Visual Basic"
        Me.Controls.Add(TextBox1)
    End Sub

But that's just a start. To go further, we're going to have to create our own classes and objects.