Question Initialisation of an Array of a class within a class

[ballybeg]

All,

I know this issue has been asked and answered a few times on the net, but I can seem to fin an answer that applies to my case.

I have main class of Races with mulitple properties. One of those properties has been defined as another class Runners.

So I have a race with multiple runners and when I try to update the data i get an instantiation error.

For the life of me I can't get it to work.

This is what I am trying to do...

In the clsRace class I have defined :

[FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff]Public[/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff]Property[/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][FONT=Consolas][SIZE=2][FONT=Consolas][SIZE=2] clsRunner([/SIZE][/FONT][/SIZE][/FONT][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff]ByVal[/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][FONT=Consolas][SIZE=2][FONT=Consolas][SIZE=2] index [/SIZE][/FONT][/SIZE][/FONT][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff]As[/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff]Long[/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][FONT=Consolas][SIZE=2][FONT=Consolas][SIZE=2]) [/SIZE][/FONT][/SIZE][/FONT][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff]As[/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][FONT=Consolas][SIZE=2][FONT=Consolas][SIZE=2] clsRunner[/SIZE][/FONT][/SIZE][/FONT][FONT=Consolas][SIZE=2][FONT=Consolas][SIZE=2]    
[/SIZE][/FONT][/SIZE][/FONT][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff]Get[/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT]
[FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff]Return[/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][FONT=Consolas][SIZE=2][FONT=Consolas][SIZE=2] m_clsRunner(index)[/SIZE][/FONT][/SIZE][/FONT]
[FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff]End[/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff]Get[/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT]
[FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff]Set[/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][FONT=Consolas][SIZE=2][FONT=Consolas][SIZE=2]([/SIZE][/FONT][/SIZE][/FONT][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff]ByVal[/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][FONT=Consolas][SIZE=2][FONT=Consolas][SIZE=2] value [/SIZE][/FONT][/SIZE][/FONT][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff]As[/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][FONT=Consolas][SIZE=2][FONT=Consolas][SIZE=2] clsRunner)[/SIZE][/FONT][/SIZE][/FONT]
[FONT=Consolas][SIZE=2][FONT=Consolas][SIZE=2]       m_clsRunner(index) = value
[/SIZE][/FONT][/SIZE][/FONT][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff]End[/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff]Set[/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT]
[FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff]End[/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff]Property[/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT]

[FONT=Consolas][SIZE=2][FONT=Consolas][SIZE=2] 
[FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff]Dim[/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][FONT=Consolas][SIZE=2][FONT=Consolas][SIZE=2] oRace [/SIZE][/FONT][/SIZE][/FONT][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff]As[/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff]New[/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][FONT=Consolas][SIZE=2][COLOR=#2b91af][FONT=Consolas][SIZE=2][COLOR=#2b91af][FONT=Consolas][SIZE=2][COLOR=#2b91af]clsRace[/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT]
[/SIZE][/FONT][/SIZE][/FONT][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff]For[/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][FONT=Consolas][SIZE=2][FONT=Consolas][SIZE=2] intCount = 1 [/SIZE][/FONT][/SIZE][/FONT][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff]To[/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][FONT=Consolas][SIZE=2][FONT=Consolas][SIZE=2] intRunners[/SIZE][/FONT][/SIZE][/FONT]
[FONT=Consolas][SIZE=2][FONT=Consolas][SIZE=2]            oRace.clsRunner(intCount).TabNo = 1 'etc etc 'ERROR HITS HERE.  
[/SIZE][/FONT][/SIZE][/FONT][FONT=Consolas][SIZE=2][FONT=Consolas][SIZE=2]next intcount
        
[/SIZE][/FONT][/SIZE][/FONT][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff][FONT=Consolas][SIZE=2][COLOR=#0000ff]Next[/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][/COLOR][/SIZE][/FONT][FONT=Consolas][SIZE=2][FONT=Consolas][SIZE=2] intCount[/SIZE][/FONT][/SIZE][/FONT]

I have defined clsRunners as a separate class. What I want to do is have a race, with an array of runners...I know I cannot use the NEW keyword with an array so I am stuck...

 

[jmcilhinney]

You're going about this the wrong way. Your Race class should not have an indexed property named Runner. It should have a property named Runners that returns a collection. That collection has an indexed Item property that will get or set a single Runner object. That's how it's done throughout the .NET Framework. Think about the Control.Controls property, which is a collection of child controls. Think about the DataSet.Tables property, which is a collection of DataTables. Think about the DataTable.Columns and DataTable.Rows properties, which are collections of DataColumns and DataRows respectively. There are many, many more examples of the same pattern too. In your case, your Race class should look something like this:

Public Class Race

    Private _runners As New List(Of Runner)

    Public ReadOnly Property Runners() As List(Of Runner)
        Get
            Return _runners
        End Get
    End Property

End Class

You can then use it something like this, which is the sort of code you will have seen many times before:

myRace.Runners.Add(New Runner)

myRunner = myRace.Runners(0)

myRace.Runners(0) = myRunner

If you want to you can declare your own collection class instead of using the standard List(Of T). If you intend to expose your Race class to other applications then you should do so.

Public Class RunnerCollection
    Inherits System.Collections.ObjectModel.Collection(Of Runner)
End Class

Public Class Race

    Private _runners As New RunnerCollection

    Public ReadOnly Property Runners() As RunnerCollection
        Get
            Return _runners
        End Get
    End Property

End Class

 

[ballybeg]

Thanks for the direction, solved my problem

Thanks Jim, very helpful as always...

I have started off by changing the Runner index to a List of Runner objects that I can now add an retrieve data from successfully.

As I want to expose the Race Class to other applications I want to follow up your second suggestion regarding the creation of a collection class...

Just to make sure I have it correctly, 1) I create the Runner Collection Class as you outlined 2) add to the Runner collection class along these lines:

oRace.Runners.Add(New clsRunner With {.TabNo = Box(intCount + 2, 0), .Scratched = fnScratchFix(Box(intCount + 2, 1)), .Name = Box(intCount + 2, 2), .JdtName = Box(intCount + 2, 3)......

What is the advantage in following the second method? Your first suggestion worked fine, couldn't I just expose the List of Runners within the Race Class?

Thanks again

ballybeg

 

[JohnH]

Why we don’t recommend using List<T> in public APIs

Using a derived class also means you can make changes to it internally without breaking its external interface.
If you used a List(Of T) and figured you had to add something to it you would have to make a derived class, which would mean you had to change all the places that used the List(Of T) to you new type also.

 

[ballybeg]

Ok, thanks John. I understand now - and that is an important consideration for my application.

Love this forum! Full of experts willing to help without the high hat. Keep up the good work.

ballybeg