Classes

[nishds2]

What are the benefits of using classes rather than using public variables, subs and functions. Whats the key thing that I'm missing that makes them so good ???

[Muddy]

Originally posted by nishds2
What are the benefits of using classes rather than using public variables, subs and functions. Whats the key thing that I'm missing that makes them so good ???

pros: Inheritance, methods, events, readonly properties, to name a few

con is that they are slower (at least they were in VB6)

[hellswraith]

You missed one, a big one by my standards: You can reuse them over and over again without having to copy and paste code. You know it works, so you won't need to spend the extra time testing after the first time.

They are a tad bit slower, but not much. VB is now fully OO so the overhead you had with VB6 has been sliced WAY down.

[Cander]

Everything is a class in VB .NET now anyway, so it is kinda of a moot point anyway..

[nishds2]

So if I had code something like as follows:

Type car
colour As String
fuel As Integer
engineRunning As Boolean
End Type

Public cars(0 to 9) As car

Function getFuel(carId As Integer) As Integer
getFuel = car(carId).fuel
End Function

Sub startEngine(carId As Integer)
engineRunning = True
End Sub


As I see it this enables me to have 10 different cars and to retrieve and set values from them individually.

Is this the sort of thing that classes are useful for and if so then how do they help

[Edneeis]

For one you can associate the methods with the type better with a class. And use properties for more control of their access.

Public Class car
 
Private _colour As String
Private _fuel As Integer
Private _engineRunning As Boolean
 
Public Property Colour() as string
  Get
     Colour=_colour
  End Get
  Set(ByVal Value as string)
     _colour=Value
  End Set
End Property
 
Public Property Fuel() as Integer
  Get
     Fuel=_Fuel
  End Get
  Set(ByVal Value as Integer)
     _Fuel=Value
  End Set
End Property
 
Public Sub startEngine()
'now this can only be changed via this method which gives you more control
 _engineRunning = True
End Sub
 
Public Sub StopEngine()
  _engineRunning=false
End Sub
 
End Class
 
Public cars(9) As New car()'I wont go into the usefulness of constructors here
 
getFuel = car(carId).fuel
 
car(carId).StartEngine

And here is a sample of the wonderfulness of inheritence:

Public Class Van
   Inherits Car
 
Public Cargo as integer
End Class
 
Public vans(9) as new van()
 
vans(vanid).startEngine()'automatically has the methods and properties of the car class
 
vans(vanid).cargo=5 'plus its own

There is more but really you have to pick what is going to best suit your needs for the project at end, whether it be a class or a structure.

[nishds2]

Ok thats great, but still a couple of things. Where exactly in my project would I put this. Do I just have a separate .vb file for all my classes and put them all one under the other, cars then vans underneath etc. Does it need to be contained within a module or can it just be on its own in the .vb file.

Also where would the Public cars(9) As New car() code go. And if I want to access / set a property in code do I need a dim... before getFuel = car(carId).fuel & car(carId).StartEngine will work

[Edneeis]

Classes can be in any file either in a module file, form file, class file, just put it outside of the Module..End Module, Form...End Form, Class...End Class. Really all files are just vb files.

After you lay down the code for the class the rest works just like you would for a type, structure, or any object in VB6. Except you put the New keyword when declaring them (which you also have to do with structures, which replaced types in .NET).

[nishds2]

So in the following code could you put in the Public cars(9) As New car() where ever it goes and also a line to set a property and a line to get a property where I put the comments.


Imports System
Imports System.Windows.Forms
Imports System.Drawing

Module Main

Sub Main
Dim fMainForm As New MainForm
fMainForm.ShowDialog()
End Sub

Public Class MainForm
Inherits System.Windows.Forms.Form

Public Sub New
MyBase.New()
Me.WindowState = 2 'Maximize
End Sub

Private Sub fMainForm_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Load

'CODE TO SET PROPERTY

someSub
End Sub

Public Sub someSub()

'CODE TO GET PROPERTY

End Sub

End Class

End Module

Public Class car

Private _colour As String
Private _fuel As Integer
Private _engineRunning As Boolean

Public Property Colour() as string
Get
Colour=_colour
End Get
Set(ByVal Value as string)
_colour=Value
End Set
End Property

Public Property Fuel() as Integer
Get
Fuel=_Fuel
End Get
Set(ByVal Value as Integer)
_Fuel=Value
End Set
End Property

Public Sub startEngine()
'now this can only be changed via this method which gives you more control
_engineRunning = True
End Sub

Public Sub StopEngine()
_engineRunning=false
End Sub

End Class

Thanks

[Edneeis]

Imports System
Imports System.Windows.Forms
Imports System.Drawing
 
Module Main
 
Sub Main
Dim fMainForm As New MainForm
fMainForm.ShowDialog()
End Sub
 
Public Class MainForm
Inherits System.Windows.Forms.Form
 
'make an array of car objects
Public cars(9) As New car() 
 
Public Sub New
MyBase.New()
Me.WindowState = 2 'Maximize
End Sub
 
Private Sub fMainForm_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Load
 
'CODE TO SET PROPERTY
cars(3).colour="Red"
 
 
someSub
End Sub
 
Public Sub someSub()
 
'CODE TO GET PROPERTY
Msgbox(cars(3).colour)
'or
dim temp as string=cars(3).colour
 
End Sub
 
End Class
 
End Module
 
Public Class car
 
Private _colour As String
Private _fuel As Integer
Private _engineRunning As Boolean
 
Public Property Colour() as string
Get
Colour=_colour
End Get
Set(ByVal Value as string)
_colour=Value
End Set
End Property
 
Public Property Fuel() as Integer
Get
Fuel=_Fuel
End Get
Set(ByVal Value as Integer)
_Fuel=Value
End Set
End Property
 
Public Sub startEngine()
'now this can only be changed via this method which gives you more control
_engineRunning = True
End Sub
 
Public Sub StopEngine()
_engineRunning=false
End Sub
 
End Class

[nishds2]

is the array only visible from within the class. Can it be accessed from other classes and if so, how

[Edneeis]

From what class? The way I have it it is only public to the MainForm but you can move that line to the Module if you need it public to the whole project.

Imports System
Imports System.Windows.Forms
Imports System.Drawing
 
Module Main
 
'make an array of car objects AVAILABLE TO WHOLE APP
Public cars(9) As New car() 
 
Sub Main
Dim fMainForm As New MainForm
fMainForm.ShowDialog()
End Sub
 
End Module
 
 
'YOU MAY NEED AN IMPORTS TO REFERENCE IT DIRECTLY NOT SURE
Imports Main
 
Public Class MainForm
Inherits System.Windows.Forms.Form
 
Public Sub New
MyBase.New()
Me.WindowState = 2 'Maximize
End Sub
 
'THE REST OF THE CODE HERE

[nishds2]

Thats great. Thanks for all your help.

[nishds2]

The Public cars(9) As New Car() line doesnt seem to work. It says Arrays cannot be declared with New

[Edneeis]

Sorry forgot about that, well you can either use a collection instead of an array, wait until you use a car the first time and then call its New constructor, or declare all 9 elements in the dim statement.

'Option 2
dim cars(9) as car
 
'before you use an element
cars(3)=New car
 
'Option 3
Dim cars() As car= {New car(), New car(), New car(), New car(), New car(), _
              New car(), New car(), New car(), New car(), New car()}
 
'then you are all set
MsgBox(cars(2).fuel)

[nishds2]

Thanks again that works fine