Objects and Classes Creating your own class

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Objects and ClassesCreating your own class
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You should be able to

• Understand how to
• write a simple class.
• use a class to create multiple objects.

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Building our own Class

• We will build a dice class.
• It will have a face value property.
• The dice will be able to roll, and this will
  change the face value.

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Dice Class (CDice)
Class
Object (Instance of a Class)

• Attributes
• Face Value
• Methods
• Roll

CDice faceValue Integer roll
(CDice) 4
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Creating the Dice Class

• Let the program know we are creating a class.
• Put code in a class module (Project gt Add Class).
• Give the class a name this is the data type
  (i.e. Integer, String, CDice).
• VB will add some code into the class file
• Public Class CDice
• End Class
• Note Naming conventions
• we usually start a class name with a capital C.

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• Declare the properties.
• Public faceValue As Integer
• Declare the procedures.
• Public Sub roll()
• End Sub
• This procedure will alter the faceValue property
  of the dice object.
• Notice the scope - Public

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• ' class CDice
• Public Class Cdice
• Public faceValue As Integer
• Public Sub roll()
• ' randomly change the faceValue
• ' must be to an integer between 1 and 6
• ' can be the same as the previous value
• End Sub
• End Class

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Rolling the dice how?

• Roll the dice,
• i.e.
• Choose a random number between 1 and 6.
• Rnd
• Generates a random number between 0 and 1
  (includes 0, but not 1).
• Value Rnd(optional number)
• We will use it without the optional number. Look
  at the help for the Rnd Function for more
  details.
• Value Rnd()

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Rolling the dice

• Randoms in programming are not real randoms, but
  are generated from a pseudo random list.
• We must choose where to start in this list...
• Randomize
• Initialises the random number generator based on
  the time.
• Randomize()
• Initialises the random number generator based on
  a seed number.
• Randomize(optional number)

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Rolling the dice

• ' initialise random number generator
• Randomize()
• ' generates a random number between 0 1
• Value Rnd()
• But we want an integer between 1 6 (inclusive)!
• Start by getting a number between 1 and 6...
• Then convert this to an integer

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An integer between 1 6

• Change the range...
• Value Rnd() between 0.00 and 0.99
• 6Value between 0.00 and 5.99 (not including 6)
• Change the start value (min)
• 6Value 1 between 1.00 and 6.99
• So...
• NewValue 6Value 1
• Then, convert to an integer
• IntValue Int(NewValue)

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An integer between 1 6

• So...
• ' initialise random number generator
• Randomize()
• ' generates a random number between 0 1
• Value Rnd()
• ' change the range
• NewValue 6Value 1
• ' convert to an integer
• IntValue Int(NewValue)
• OR...
• Randomize()
• ' generates a random number between 0 1
• IntValue Int( 6 Rnd() 1 )

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Rolling the dice

• IntValue Int( 6 Rnd() 1 )
• More generally...
• Converting Random numbers
• Convert the number to an integer between min and
  max inclusive
• IntValueInt( (max-min 1)Rnd() min)
• Think through this expression. What happens with
  min1 and max6? When Rnd() gives 0 and when
  Rnd() gives 0.99?

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• ' class CDice
• Public Class Cdice
• Public faceValue As Integer
• Public Sub roll()
• Dim Value As Double
• Const min As Integer 1
• Const max As Integer 6
• ' initialise random number generator
• Randomize()
• ' Rnd generates a random number between 0 and
  1
• Value Rnd()
• ' convert random number to be an integer
• ' between 1 and 6 inclusive
• faceValue Int( (max-min 1)Value min)
• End Sub

This is the Public variable declared above.
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Using the Dice Class Declaring Creating Objects

• Declare name for Object of a specific type/class
• This declares a name to use to refer to the
  object.
• Use Public, Dim etc. to get the right scope.
• CDice should appear in the code complete window
  as a data type.
• Public myDice As CDice
• Create (instantiate) object of a specific
  type/class
• use the New keyword
• myDice New CDice
• Note Naming conventions
• we usually start object names with a lower case
  letter.

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Using the Dice Class

• We will create the dice object when the form is
  loaded.
• When we click on a roll button we want the dice
  object to perform a roll action the face value
  should change.
• We can then ask the dice object for the current
  face value and display this on the form.

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Many Dice Form
cmdGo
lblDice2
lblDice3
lblDice1
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• Form code
• Windows Form Designer generated code
• ' declare myDice object of type (class) CDice
• Public myDice1 As CDice
• Private Sub Form1_Load(... ) Handles ...
• ' create a new CDice object called myDice
• myDice1 New CDice
• End Sub
• Private Sub cmdRoll_Click(... ) Handles ...
• ' call the roll action of the myDice object
• myDice1.roll()
• ' display the faceValue property of myDice
• lblDice1.Text CStr(myDice1.faceValue)
• End Sub

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Creating more than 1

• We could create many objects of the type CDice,
  all would have the same properties and methods,
  but their own individual state.
• Once the class has been written, we do not have
  to worry about how the methods are implemented,
  only how to use them.

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Creating more than 1

• Declare more then one object name and type
• Public myDice1 As CDice
• Public myDice2 As CDice
• Create more than one object
• myDice1 New CDice
• myDice2 New CDice
• Roll and display more than one Dice
• ' call the roll action of the CDice objects
• myDice1.roll()
• myDice2.roll()
• 'display the faceValue of the Cdice objects
• lblDice1.Text CStr(myDice1.faceValue)
• lblDice2.Text CStr(myDice2.faceValue)

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Useful VB

• Randomize
• Initialises the random number generator based on
  the time.
• Randomize
• Rnd
• Generates a random number between 0 and 1
  (includes 0, but not 1).
• Number Rnd(optional number)
• Converting Random numbers
• Convert the number to an integer between min and
  max inclusive
• IntNumber Int(Value (max - min 1) min)

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You should be able to

• Understand how to
• write a simple class.
• use a class to create multiple objects.