[2005] Multiple Instances of a Custom Class

[Duckfather]

Hi all

I have a sub that runs on a button click which I want to create a new instance of a custom class and add it to a list of already created instances of this class. I want the result to be a List Of collection of all of my class instances.

My problem is that each time I run the sub, it simply 'overwrites' the first instance of the class and adds a copy of it to the list instead of writing a new instance. My code is along these lines :-

dim objFixture as new clsFixture

For n As Integer = 1 To intNoOfChannels
     objFixture.SetChannelAddress(n, intCurrentChannelTotal + 1)
     intCurrentChannelTotal += 1
next

lstFixtures.Add(objFixture)

Can anyone let me know what I'm obviously doing wrong?

Hope that makes sense

Andy

[Shaggy Hiker]

There's nothing obviously wrong with what you have posted. It does appear that two classes built in this fashion would be highly similar, based on my guess as to what SetChannelAddress does. Therefore, I would next pursue these two paths:

1) How can you tell that the new class overwrites the first, and how can you tell that the other class is a copy?

2) Are there any events or other things that might tie the two objects together such that changing one object can cause changes in the other object?

Edit: Also, I assume that lstFixtures is defined as List (of clsFixture). If that's not the case, then what is it?

[Duckfather]

Sorry for not explaining fully

Basically, the SetChannelAddress routine builds an array of Channel values. The first time the code is executed, the instance gets assigned values 1 - 5. The next time the code is executed, the new instance should get assigned values 6 - 10. I should end up with two instances, the first one holding values 1 - 5 and the second holding 6 - 10.

What actually happens when I step through the code and examine the List is that I end up with two instances in the List, each one containing values 6 - 10. I can actually see the first instance (which is already in the List) getting overwritten as the loop is executed (the first loop iteration for the second instance shows that my Channel values are 6,2,3,4,5 on the existing instance in the List for example).

There's no other code that accesses the List or class instance and nothing that could tie the instances together.

lstFixtures is indeed defined as a List (of clsFixture)

I'm stumped

[Shaggy Hiker]

Post the definition of SetChannelAddress, and the constructor (Sub New) for clsFixture, if there is one.

This type of question always has the same answer, but in your case it is MUCH more difficult to find than it normally would be. For some reason, all the classes that are being created have the same array. Somewhere in the code there is a line that does this:

arrayX = arrayY

It may not look like that, but it is there, in some fashion. The most likely sources for this are in the constructor for clsFixture, and the SetChannelAddress method.

[Duckfather]

It's a pretty simple class :-

Public Class clsFixture

    Private strName As String
    Private strManufacturer As String
    Private imgPicture As Image
    Private strDescription As String
    Private strFilename As String
    Private intType As Integer
    Private intNoOfChannels As Integer = 0
    Private arrChannelTypes() As Integer
    Private arrChannelDMXAddress() As Integer

    Public Sub New()
        arrChannelTypes = Nothing
        arrChannelDMXAddress = Nothing
    End Sub

    Public Property Name() As String
        Get
            Return strName
        End Get
        Set(ByVal value As String)
            strName = value
        End Set
    End Property

    Public Property Manufacturer() As String
        Get
            Return strManufacturer
        End Get
        Set(ByVal value As String)
            strManufacturer = value
        End Set
    End Property

    Public Property Picture() As Image
        Get
            Return imgPicture
        End Get
        Set(ByVal value As Image)
            imgPicture = value
        End Set
    End Property

    Public Property Description() As String
        Get
            Return strDescription
        End Get
        Set(ByVal value As String)
            strDescription = value
        End Set
    End Property

    Public ReadOnly Property StartAddress() As Integer
        Get
            Return arrChannelDMXAddress(0)
        End Get
    End Property

    Public Property Type() As Integer
        Get
            Return intType
        End Get
        Set(ByVal value As Integer)
            intType = value
        End Set
    End Property

    Public Property Filename() As String
        Get
            Return strFilename
        End Get
        Set(ByVal value As String)
            strFilename = value
        End Set
    End Property

    Public Property NoOfChannels() As Integer
        Get
            Return intNoOfChannels
        End Get
        Set(ByVal value As Integer)
            intNoOfChannels = value

            ReDim arrChannelDMXAddress(intNoOfChannels - 1)
            ReDim arrChannelTypes(intNoOfChannels - 1)

        End Set
    End Property

    Public Sub SetChannelAddress(ByVal Channel As Integer, ByVal Address As Integer)
        arrChannelDMXAddress(Channel - 1) = Address
    End Sub

    Public Sub SetChannelType(ByVal Channel As Integer, ByVal Type As String)
        arrChannelTypes(Channel - 1) = Type
    End Sub

End Class

[Shaggy Hiker]

Hmmm, still see nothing. That IS a simple class. Very interesting.

The next thing I would try would be to put a breakpoint on this line from your first post:

For n As Integer = 1 To intNoOfChannels

When the breakpoint is reached, I would examine the object in the list in detail (ok, I guess you'd have to reach that line the second time for anything to be in the list). Does it have the 1-5 that it should have? If so, I would then step through the code using F10 to skip over the functions, or else put a breakpoint on the .Add method, and at the point of the Add, I would look at the object that was just created to confirm that it holds 6-10, and look again at the object in the list to see whether it still holds 1-5.

If it was 1-5 at the first check (before the loop is run), then changes to 6-10 by the time of the Add, then I would repeat those steps and watch for when the existing object changes values. If it was 1-5 at the first check, then is STILL 1-5 at the Add, then I would check immediately AFTER the add, at which point it should not have changed at all.

[Duckfather]

Ok, so I've found the problem!

It's been down to how the initial object was created and properties set (which I omitted from the example code as I considered it irrelevant to the problem )

The actual application is for controlling light fixtures (as in for stage shows etc). These lights have multiple channels to control different properties such as brightness, red, green, blue, strobe etc, each one having a specific address assigned to it (using what's called the DMX512 protocol for lighting). The class only has to be for holding the light's settings for later use, hence the simplicity.

I already had a List of available fixtures set up (without any values for the channels or channel addresses, but apart from theat exactly the same as lstFixtures) using the same class. I was then using the available fixture list and picking what fixtures I actually wanted to control. The problem came when I created the new fixture from the available fixture list. I was assigning the new fixture to be equal to the specific one in the available fixture list.

Dim objFixture As New clsFixture

objFixture=lstAvailableFixtures(index)

For n As Integer = 1 To intNoOfChannels
     objFixture.SetChannelAddress(n, intCurrentChannelTotal + 1)
     intCurrentChannelTotal += 1
Next

This obviously tied any other instances of this same fixture together, so whenever I changed a value, all other corresponding values in the other clone fixtures changed

I've fixed it by assigning the properties of the new fixture to be equal to the properties of the available fixture instead of making it directly equal to the actual object.

Dim objFixture As New clsFixture

With objFixture
     .NoOfChannels=lstAvailableFixtures(strFixtureTag).NoOfChannels
     .Manufacturer = lstAvailableFixtures(strFixtureTag).Manufacturer
     .Description = lstAvailableFixtures(strFixtureTag).Description
     .Picture = lstAvailableFixtures(strFixtureTag).Picture
Next

For n As Integer = 1 To intNoOfChannels
     objFixture.SetChannelAddress(n, intCurrentChannelTotal + 1)
     intCurrentChannelTotal += 1
Next

Schoolboy error which I should have noticed (well, never done it in the first place would have been preferable )

Thanks for your help

Andy

[Shaggy Hiker]

Glad to hear that. As I said before, the answer to this type of problem is always the same...you just have to find it.