dynamic array of class

Hi
Is it possible to create array of a class. 'But a unspecified number of elements

e.g Dim A() as String '(This creates a array of strings with a unspecified number of elements)

But !!

e.g Dim MyForm() As System.Windows.Forms.Form
Dim a As Integer = 2
Redim MyForm(a)
MyForm(1).Text = "Hello" ***No instance of class Form exception occurs****


I cannot reference a instance of a class in the array, any ideas why ?

Yes you can create array of class but you have to declare the all the methods as shared (because you can declare arrays with New keyword ) .

bts its a class of type form and form already has all its methids declared

Quote:

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Originally posted by SmagO
Hi
Is it possible to create array of a class. 'But a unspecified number of elements

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I meant this !

String is a value type not a reference type variable thus it doesn't require the New keyword to make a new instance. When declaring arrays of reference types the array does not declare new instances of the objects you must do this for each element in the array. You can do it at declaration but you would have to know how many instances or just individually as you add the elements to the array.

VB Code:

'specificied type but haven't created any instances
        Dim frms() As Form3
        ReDim frms(1)
        'create an instance for the new elements
        frms(0) = New Form3()
        frms(1) = New Form3()
        'now its safe to use
        frms(0).Show()

Quote:

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String is a value type not a reference type variable thus it doesn't require the New keyword to make a new instance.

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Actually, the System.String class is a reference type. Behind the scenes, a string object is allocated on the heap, rather than the stack. For instance, if we assign one string variable to another string, we get two disparate references to the same string in memory. However, if we make changes to one of the strings, an entirely new string object will be placed on the heap.

Thus, this is why massive string manipulation with a typical string type is frowned upon, welcoming the StringBuilder class a much better substitute.

Hmm, I didn't know that. I thought all of the basic data types were value types. Thanks.

How come you don't have to use New with strings?

Because the = (and other operators) operator have been overloaded.

is it maybe just that you cant have an array of objects?

Why not use an ArrayList, or similiar collection class, instead, you can add what you like and it grows with your needs.

Hehe... I actually did something like this today, tried making an array of classes... well, I ended up making a class that holds a collection of class instances...

Take a look at the MSDN step-by-step below, it really helped me out:

"In this walkthrough, you use the CollectionBase class to create a class called WidgetCollection. This is a collection that accepts only widgets, and exposes its members as Widget types, instead of accepting objects and exposing members as Object type. You then implement methods to add widgets to your collection and to remove the widget at a specific index, and you also implement an Item property that returns the widget object at the appropriate index. "

http://msdn.microsoft.com/library/de...ctionClass.asp

With this help, I was able to create an instance of an invoice, and add instances of invoiceitems (items that belong to the sale), and have the whole collection of invoiceitems internal to the invoice itself. So to add an invoiceitem (which is a class instance since an item contains name, style, price, cost, color,etc), I simply used:

VB Code:

Dim r As Invoice = New Invoice() 'declare a new invoice
 
        Dim invItem1 As InvoiceItem = New InvoiceItem("Elran", 2, "Assisa", _ 
3, 1, "Sofa", 200, 30, 10, 20) 'declare new invoice item instance
        Dim invItem2 As InvoiceItem = New InvoiceItem("Legacy", 2, "Apachea", _
 3, 1, "Sofa", 200, 20, 10, 15) 'declare another invoice item instance
        r.Add(invItem1) 'add item to invoice
        r.Add(invItem2) 'add item to invoice