VB.NET 在 XML 输出中序列化和写入 NULL 节点标签

问题描述

我正在将 VB.net 类序列化为 XML。一个条件是我必须包含 NULL Elements/Nodes 当序列化的 XML 中没有类数据时。为了玩弄这个概念，我修改了 Microsoft 站点上的示例，其中包含采购订单示例。我已将其修改为 在 OrderedItem 类中包含一个子类 (ItemLocation)。也试验了这个类 当它没有类数据时 -- IsNull。

我在 ItemLocation 类定义中使用以下内容 公共组作为字符串

当我有一个没有数据的 ItemLocation

我得到以下 XML 输出

  <Stores>
    <ItemLocation xsi:nil="true" />
    <ItemLocation xsi:nil="true" />
  </Stores>

我想知道是否可以在我的 XML 输出中生成类似的内容

--或--

  <Stores>
    <StoreLocation/>
    <StoreName/>
  </Stores>


My Vb.NET Program

<XmlRootAttribute("PurchaSEOrder",Namespace:="http://www.cpandl.com",IsNullable:=False)>
Public Class PurchaSEOrder
    Public ShipTo As Address
    Public OrderDate As String
    ' The XmlArrayAttribute changes the XML element name
    ' from the default of "OrderedItems" to "Items". 
    <XmlArrayAttribute("Items")>
    Public OrderedItems() As OrderedItem
    Public SubTotal As Decimal
    Public ShipCost As Decimal
    Public TotalCost As Decimal
End Class


Public Class Address
    ' The XmlAttribute instructs the XmlSerializer to serialize the Name
    ' field as an XML attribute instead of an XML element (the default
    ' behavior). 
    <XmlAttribute()>
    Public Name As String
    Public Line1 As String

    ' Setting the IsNullable property to false instructs the
    ' XmlSerializer that the XML attribute will not appear if
    ' the City field is set to a null reference. 
    <XmlElementAttribute(IsNullable:=False)>
    Public City As String
    Public State As String
    Public Zip As String
End Class

Public Class OrderedItem
    Public ItemName As String
    Public Description As String
    Public UnitPrice As Decimal
    Public Quantity As Integer
    Public Linetotal As Decimal
    <XmlArrayAttribute("Stores")>
    Public ItemLocation() As ItemLocation

    ' Calculate is a custom method that calculates the price per item,' and stores the value in a field. 
    Public Sub Calculate()
        Linetotal = UnitPrice * Quantity
    End Sub
End Class

Public Class ItemLocation
    <XmlElement(IsNullable:=True)> Public Group As String
    Public StoreName As String
    Public StoreCity As String
End Class

Public Shared Sub Main()
        ' Read and write purchase orders.
        Dim t As New test()
        t.CreatePO("C:\Users\someuser\Downloads\vb_dump\out.xml")
End Sub

Private Sub CreatePO(filename As String)
        ' Create an instance of the XmlSerializer class;
        ' specify the type of object to serialize.
        Dim serializer As New XmlSerializer(GetType(PurchaSEOrder))
        Dim writer As New StreamWriter(filename)
        Dim po As New PurchaSEOrder()

        ' Create an address to ship and bill to.
        Dim billAddress As New Address()
        billAddress.Name = "Teresa Atkinson"
        billAddress.Line1 = "1 Main St."
        billAddress.City = "AnyTown"
        billAddress.State = "WA"
        billAddress.Zip = "00000"
        ' Set ShipTo and BillTo to the same addressee.
        po.ShipTo = billAddress
        po.OrderDate = System.DateTime.Now.ToLongDateString()

        ' Create an OrderedItem object.
        Dim items(1) As OrderedItem
        Dim i1 As New OrderedItem()
        i1.ItemName = "Widget S"
        i1.Description = "Small widget"
        i1.UnitPrice = CDec(5.23)
        i1.Quantity = 3
        i1.ItemLocation = New ItemLocation(1) {} ' Initialize ItemLocation
        i1.Calculate()

        Dim stores(1) As ItemLocation
        Dim s1 As New ItemLocation()
        s1.StoreName = "Target"
        s1.StoreCity = "MyCity"
        stores(0) = s1
        i1.ItemLocation(0) = stores(0)

        ' Insert the item into the array.
        items(0) = i1

        Dim i2 As New OrderedItem()
        i2.ItemName = "Widget x"
        i2.Description = "Extra Small widget"
        i2.UnitPrice = CDec(500.23)
        i2.Quantity = 100
        i2.ItemLocation = New ItemLocation(1) {} ' Initialize ItemLocation
        i2.Calculate()
        Dim s2 As New ItemLocation()
        stores(1) = s2
        i1.ItemLocation(1) = stores(1)

        ' Insert the item into the array.
        items(1) = i2

        po.OrderedItems = items

        ' Calculate the total cost.
        Dim subTotal As New Decimal()
        Dim oi As OrderedItem
        For Each oi In items
            subTotal += oi.Linetotal
        Next oi
        po.SubTotal = subTotal
        po.ShipCost = CDec(12.51)
        po.TotalCost = po.SubTotal + po.ShipCost
        ' Serialize the purchase order,and close the TextWriter.
        serializer.Serialize(writer,po)
        writer.Close()
    End Sub

解决方法

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