Vb.Net instantiate a Property of a class that is an array of a different class

Question

This is for the purpose of Serializing and Deserializing an Xml object

<XmlRoot("orderadd")>
<Serializable()> _
Public Class clsSMsgRequestMessage
    <XmlElementAttribute()> Public Property ordertype() As String
    <XmlElementAttribute()> Public Property vehicleid() As String
    <XmlElementAttribute()> Public Property orderpriority() As String
    <XmlElementAttribute("orderpart")> Public Property orderpart() As RequestMessageOrderaddOrderpart()
    <XmlAttributeAttribute()> Public Property clientid() As String
    <XmlAttributeAttribute()> Public Property transactionid() As String
    <XmlAttributeAttribute()> Public Property numberoforderparts() As String

    Public Sub New()
    End Sub
End Class

Public Class RequestMessageOrderaddOrderpart
    <XmlElementAttribute()> Public Property operation() As String
    <XmlElementAttribute()> Public Property location() As String
    <XmlElementAttribute()> Public Property loadtype() As String
    <XmlAttributeAttribute()> Public Property orderpartnumber() As String

    Public Sub New()
    End Sub

End Class

This works correctly for deserializing, but now I am trying to create this object correctly so I can serialize it back to an XML object.

Dim anotherTest As clsSMsgRequestMessage = New clsSMsgRequestMessage()
Dim testOrderPart1 As New RequestMessageOrderaddOrderpart


anotherTest.clientid = "data"
anotherTest.orderpriority = "data"
anotherTest.ordertype = "data"
anotherTest.transactionid = "data"
anotherTest.vehicleid = "data"
anotherTest.numberoforderparts = "data"

testOrderPart1.loadtype = "data"
testOrderPart1.location = "data"
testOrderPart1.operation = "data"
testOrderPart1.orderpartnumber = "data"


anotherTest.orderpart(0) = testOrderPart1

The last line here doesn't work because anotherTest.orderpart(0) isn't instantiated yet. But I don't know how to instantiate it because

anotherTest.orderpart(0) = New RequestMessageOrderaddOrderPart

still comes back with a "Object reference not set to an instance of an object."

anotherTest.orderpart = New RequestMessageOrderaddOrderPart

comes back with "Value of type cannot be converted to '1-dimensional array of "

I think I'm on the right track with instantiating it by itself like I'm doing with 'testOrderPart1' but I don't know how to link that to my anotherTest.orderpart

Please help!

MarcinJuraszek · Accepted Answer · 2013-03-29 12:22:27Z

2

You have to initialize your array property first:

anotherTest.orderpart = New RequestMessageOrderaddOrderPart(10) {}

10 is array size.

After that you'll be able to set first array element:

anotherTest.orderpart(0) = New RequestMessageOrderaddOrderPart

Update

However, I think you should change your property declaration to become List(Of RequestMessageOrderaddOrderPart). With a list you don't have to specify number of items:

anotherTest.orderpart = New List(Of RequestMessageOrderaddOrderPart)()

Adding items is really easy:

anotherTest.orderpart.Add(new RequestMessageOrderaddOrderPart())

And you're still able to get/modify items using indexers:

Dim firstItem = anotherTest.orderpart(0)

Of course, that item has to be inserted using Add method first.

List(Of T) will work fine with serialization as well.

edited Mar 29, 2013 at 12:22

answered Mar 29, 2013 at 12:16

MarcinJuraszek

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2 Comments

Brandon Over a year ago

oh cool thanks! Do I have to set it to a fixed size like that? basically the XML message will have a variable number of 'parts' coming back and I won't know. I suppose they'll never have more than 20 or so parts - would be okay to just initialize a huge array and then regularly not use most of them?

jbabey Over a year ago

I highly suggest using a List(Of RequestMessageOrderaddOrderpart) instead of an array

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