how do you implement association between objects

[Guest]

I am at my wits end. VB .net is supposed to be an object oriented language.
But I have tried hack after hack, and I can not get past either "Reference to
a non-shared member requires an object reference.", or "Name <object> is not
declared." or a stack overflow exception. This is simple object oriented
association. I need for objects generated by Form1, Class1, and Class2 to
talk to each other back and forth. Here is how it starts:

Imports System

Public Class Form1
Inherits System.Windows.Forms.Form

#Region " Windows Form Designer generated code "

Public Simulation As New Class1
Public CarA As New Class2
Public CarB As New Class2

Private Sub Button1_Click(ByVal sender As Object, ByVal e As
System.EventArgs) Handles Button1.Click
Simulation.update_rideList(True, 3)
End Sub

End Class

'Then the other classes:

Public Class Class1

Public Sub New()
MyBase.New()
End Sub

Public Overridable Sub update_rideList(ByVal car As Boolean, ByVal
floor As Integer)

If (car) Then
CarA.rideList.Add(floor)
CarA.test_change(True)
Else
CarB.rideList.Add(floor)
End If
End Sub

End Class

'and

Public Class Class2

Public Sub New()
MyBase.New()
End Sub

Public rideList As New ArrayList
Public Sub test_change(ByVal change As Boolean)
If (change) Then
Label1.BackColor = Label1.BackColor.Green
End If

End Sub
End Class


Please Help??!!!!

 

[Armin Zingler]

I am at my wits end. VB .net is supposed to be an object oriented
language. But I have tried hack after hack, and I can not get past
either "Reference to a non-shared member requires an object
reference.", or "Name <object> is not declared." or a stack overflow
exception. This is simple object oriented association. I need for
objects generated by Form1, Class1, and Class2 to talk to each other
back and forth. Here is how it starts:

You should have mentioned where you get the error.

Imports System

Public Class Form1
Inherits System.Windows.Forms.Form

#Region " Windows Form Designer generated code "

Public Simulation As New Class1
Public CarA As New Class2
Public CarB As New Class2

Private Sub Button1_Click(ByVal sender As Object, ByVal e As
System.EventArgs) Handles Button1.Click
Simulation.update_rideList(True, 3)
End Sub

End Class

'Then the other classes:

Public Class Class1

Public Sub New()
MyBase.New()
End Sub

Public Overridable Sub update_rideList(ByVal car As Boolean,
ByVal floor As Integer)

If (car) Then
CarA.rideList.Add(floor)
CarA.test_change(True)
Else
CarB.rideList.Add(floor)
End If
End Sub

End Class

CarA is a member of the Form. If you want to access CarA, you need a
reference to the Form that contains CarA. If you had 5 instances of the
Form, you would have 5 x CarA, so you must say ThisForm.CarA or
ThatForm.CarA. Or maybe no single Form instance exists. Which CarA would
Class1 refer to?

Solution: Pass the reference to the Form into sub update_rideList:

Public Overridable Sub update_rideList( _
ByVal car As Boolean, ByVal floor As Integer, _
ByVal TheForm As Form1)

If (car) Then
TheForm.CarA.rideList.Add(floor)
TheForm.CarA.test_change(True)
Else
TheForm.CarB.rideList.Add(floor)
End If
End Sub


Call:

Simulation.update_rideList(True, 3, Me)

'and

Public Class Class2

Public Sub New()
MyBase.New()
End Sub

Public rideList As New ArrayList
Public Sub test_change(ByVal change As Boolean)
If (change) Then
Label1.BackColor = Label1.BackColor.Green
End If

End Sub
End Class

Here's the same with Label1.



Armin

 

[rowe_newsgroups]

I am at my wits end. VB .net is supposed to be an object oriented language.

It is an object orientated language, you're just confused on how to
program using it. The errors, with the exception of the stack
overflow, tell you exactly the problem. You are trying to use a
variable unknown to a Class. There are at least two ways of fixing
this:

Public CarA As New Class2
Public CarB As New Class2

If these are the two variable you want to be visible to Class1, you
must either pass a reference to them to the instance of Class1 or make
Class1 a subclass to Form1. Making Class1 a subclass would give it
access to these two variables, but also could break your class
structure. For that reason I'll assume you are going to use the first
method (passing the reference to the class).

Public Overridable Sub update_rideList(ByVal car As Boolean, ByVal
floor As Integer)

This needs changed to the below if you want to pass the reference to
your class variables:

///////////
Public Overridable Sub update_ridelist(car As Boolean, floor As
Integer, carA as Class2, carB as Class2)
///////////

If you want to be able to access the CarA and CarB objects.

Private Sub Button1_Click(ByVal sender As Object, ByVal e As
System.EventArgs) Handles Button1.Click
Simulation.update_rideList(True, 3)
End Sub

This is where you need to pass the references to CarA and CarB. With
the above change you would call the method like this:

///////////
Simulation.update_ridelist(True, 3, CarA, CarB)
///////////

Then the CarA and CarB variables should be changed properly.

Public Sub test_change(ByVal change As Boolean)
If (change) Then
Label1.BackColor = Label1.BackColor.Green
End If
End Sub

On a side note, I find the "change" variable pointless as you don't
have an else clause. Basically, if you want the change call the
method, otherwise don't. Adding the bool check just adds overhead.

Thanks,

Seth Rowe

 

[Guest]

It's unlikely that Label1 (presumably from Form1) is exposed publicly to
Class2. Even if it is, you need to let the instance of Class2 (either carA
or CarB) to have a reference to the creating form instance.

 

[Guest]

Thank you Seth, passing the reference to the Form1 seems to have fixed it.

Incidentally, this is just a test case.

Thanks again.

 

[Guest]

Thank you, Armin, passing the reference seems to have worked. Thanks again.