Shared Dictionary variable does not save my objects

Question

I'm working on an assignment for my class where we learn to use dictionaries. I have to save the order objects to the dictionary. When I debug it gives me the NullReferenceException The orders are being created correctly, just won't be assigned to the dictionary, and then I have to display the orders to a listbox using the dictionary

Public Class MainForm

Public Shared orders As Dictionary(Of Integer, Order)

Private Sub MainForm_Load(sender As Object, e As EventArgs) Handles MyBase.Load

        Dim aOrder As Order
        'order created for Joe Jones
        aOrder = New [Order](#05/1/2017#, "Joe Jones")
        Dim sillyPuttyItem As New Item("silly putty", 3.95, 10, 2.99)
        Dim rubiksItem As New Item("Rubik's Cube", 9.1)
        aOrder.AddItem(sillyPuttyItem)
        aOrder.AddItem(rubiksItem)

        orders.Add(1, aOrder) 

        aOrder = New [Order](#12/5/2017#, "Kathy Klum")
        Dim fidgetItem As New Item("Fidget Spinner", 6.79, 5, 5.98)
        Dim bubblesItem As New Item("bottle of bubbles", 0.99)
        aOrder.AddItem(fidgetItem)
        aOrder.AddItem(bubblesItem)
        Order.orders.Add(2, aOrder)

        For Each order In orders
            lstOrders.Items.Add(orders.ToString())



Option Strict On
Option Explicit On

Public Class Order
    Public Shared orders As Dictionary(Of Integer, Order)
    Public Shared NEXT_ORDER_NUMBER As Integer = 1234
    Private Const SALES_TAX_RATE As Double = 0.08

    Private mOrderDate As DateTime
    Private mOrderNumber As Integer
    Private mName As String
    Private mQuantityOrdered As Integer
    Private mItems As New List(Of Item)

    Public Sub New(ByVal pDate As DateTime, ByVal pName As String)
        mOrderDate = pDate
        mName = pName
    End Sub

    Public ReadOnly Property OrderDate As DateTime
        Get
            Return mOrderDate
        End Get
    End Property

    Public ReadOnly Property OrderNumber As Integer
        Get
            Return mOrderNumber
        End Get
    End Property

    Public ReadOnly Property Name As String
        Get
            Return mName
        End Get
    End Property
            Next


Option Strict On
Option Explicit On


Public Class Item

    Private itemName As String
    Private itemPrice As Double
    Private bulkQuantity As Integer
    Private bulkPrice As Double

    Private mquantityOrdered As Integer

    Public ReadOnly Property QuantityOrdered As Integer
        Get
            Return mQuantityOrdered
        End Get
    End Property

    Public Sub New(ByVal pItemName As String, ByVal pPrice As Double)
        itemName = pItemName
        itemPrice = pPrice
        ' mquantityOrdered = pQuantity
    End Sub

    Public Sub New(ByVal pItemName As String, ByVal pPrice As Double,
                   ByVal pBulkQuantity As Integer, ByVal pBulkPrice As Double)

        bulkQuantity = pBulkQuantity
        bulkPrice = pBulkPrice
        '  mquantityOrdered = pQuantity
    End Sub

    Public Sub New(ByVal pItem As Item)
        itemName = pItem.Name
        itemPrice = pItem.itemPrice
        bulkQuantity = pItem.bulkQuantity
        bulkPrice = pItem.bulkPrice
    End Sub

    Public Sub New(ByVal pItem As Item, ByVal pQuantity As Integer)
        Me.New(pItem)
        mquantityOrdered = pQuantity
    End Sub

Answer 1

This

Public Shared orders As Dictionary(Of Integer, Order)

Declares the shared field orders of type Dictionary(Of Integer, Order). It doesn't actually create it. I think you are looking for:

Public Shared orders As New Dictionary(Of Integer, Order)

Notice the "New" in there.

I'm now getting the exception when adding the second order to the dictionary, but it takes the first one

Your second add is adding to different dictionary. The first one is doing:

orders.Add(1, aOrder) 

and the second is doing:

Order.orders.Add(2, aOrder)

The Order class seems to have another shared Dictionary that is also Nothing. You should either Use New Dictionary for the Dictionary in Orders, or perhaps you meant to do orders.Add(2, aOrder) and not use the shared field in Orders.