Chapter 24. Defining Class Methods and Events
Lesson 23 explains how to create a class and give it properties. In this lesson you learn how to add the remaining two key pieces of a class: methods and events.
A method is simply a subroutine or function in the class that other parts of the program can execute. The following code shows how the
Turtle drawing class described in Lesson 23 might implement its
' Make the Turtle move the indicated distance in its current direction. Public Sub Move(ByVal distance As Integer) ' Calculate the new position. Dim radians As Double = Direction * Math.PI / 180 Dim newX As Integer = CInt(X + Math.Cos(radians) * distance) Dim newY As Integer = CInt(Y + Math.Sin(radians) * distance) ' Draw to the new position. Using gr As Graphics = Graphics.FromImage(Canvas) gr.DrawLine(Pens.Blue, X, Y, newX, newY) End Using ' Save the new position. X = newX Y = newY End Sub
You can download the Turtle example program from the book's web site (at
www.vb-helper.com/24hourvb.html) as part of the Lesson24 folder and follow along in its code as you read through this lesson.
The method takes as a parameter the distance it should move. It uses the
Turtle's current position and direction to figure out where this move will terminate. It uses some graphics code to draw a line from the current position to the new one (don't worry about the details) and finishes by saving the new position.
That's all there is to adding a method to a class. ...