Object reference not set to an instance of an object

  • Thread starter Thread starter Guest
  • Start date Start date
G

Guest

Please I am trying to understand the arraylist.

Please anyone help; why I am getting this message "Object reference not set
to an instance of an object" when line no (13) get executed in the following
code:

1- ' Create a new ArrayList to hold the Customer objects.
2- Dim customerArray As New ArrayList()

3- 'Add customers to the ArrayList of Customer objects.
4- Dim x As Integer
5- For x = 0 To 999
6- customerArray.Add(New Customer("Customer" + x.ToString()))
7- Next x

8- ' Add orders to each Customer object in the ArrayList.
9- Dim customer1 As Customer
10- For Each customer1 In customerArray
11- Dim y As Integer
12- For y = 0 To 14
13- customer1.CustomerOrders.Add(New Order("Order" +
y.ToString()))
14- Next y

-----------Customer & Order Classes-----
Public Class Customer
Private _CustomerOrders As ArrayList
Private _Name As String
Public Property Name() As String
Get
Return _Name
End Get
Set(ByVal value As String)
_Name = value
End Set
End Property
Public Property CustomerOrders() As ArrayList
Get
Return _CustomerOrders
End Get
Set(ByVal value As ArrayList)
_CustomerOrders = value
End Set
End Property
Public Sub New(ByVal Name As String)
_Name = Name
End Sub
End Class
---------------
Public Class Order
Private _Name As String
Public Property Name() As String
Get
Return _Name
End Get
Set(ByVal value As String)
_Name = value
End Set
End Property
Public Sub New(ByVal Name As String)
_Name = Name
End Sub
End Class
 
Sam said:
Please I am trying to understand the arraylist.

Please anyone help; why I am getting this message "Object reference not set
to an instance of an object" when line no (13) get executed in the following
code:
Click to expand...

I can't see anything in your code which initializes customer1.
_CustomerOrders, which would certainly explain the exception. You need
to initialize the underlying ArrayList somewhere.
 
Thank you Sir.

I added the line no 4 and it works.

1 ' Add orders to each Customer object in the ArrayList.
2 Dim customer1 As Customer
3 For Each customer1 In customerArray
4 customer1.CustomerOrders = New ArrayList
5 Dim y As Integer
6 For y = 0 To 14
7 customer1.CustomerOrders.Add(New Order("Order" +
y.ToString()))
8 Next y
9 Next customer1

Thank you again.
 
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