无法将模型添加到列表

Question

我执行以下for each循环将模型插入到列表中：

        Dim weights = weight.Where(Function(x) x.FW_Food_ID = item.NDB_No)

        For Each i In weights
            Dim model = New Tbl_Food_Weight
            model.FW_GmWt = i.FW_GmWt
            Debug.Print("i.FW_GmWt=" + i.FW_GmWt)
            Debug.Print("model.FW_GmWt=" + model.FW_GmWt)
            model.FW_Food_ID = i.FW_Food_ID
            Debug.Print("i.FW_Food_ID=" + i.FW_Food_ID)
            Debug.Print("model.FW_Food_ID=" + model.FW_Food_ID)
            model.FW_Option = i.FW_Option
            Debug.Print("i.FW_Option=" + i.FW_Option)
            Debug.Print("model.FW_Option=" + model.FW_Option)
            model.FW_ID = i.FW_ID
            Debug.Print("i.FW_ID=" + i.FW_ID.ToString)
            Debug.Print("model.FW_ID=" + model.FW_ID.ToString)
            item.test.Add(model)
        Next

我的模型如下：

Public Class Tbl_Food_Weight

    <Key()> _
    Public Property FW_ID As Integer
    Public Property FW_Food_ID As String
    Public Property FW_Option As String
    Public Property FW_Serving_Size As String
    Public Property FW_GmWt As String

End Class

我的test属性如下：

<NotMapped()> _
Public Overridable Property test As List(Of Tbl_Food_Weight)

我得到的输出是：

i.FW_GmWt=250
model.FW_GmWt=250
i.FW_Food_ID=12695
model.FW_Food_ID=12695
i.FW_Option=1
model.FW_Option=1
i.FW_ID=4481
model.FW_ID=4481
A first chance exception of type 'System.NullReferenceException' occurred in MyBlog.DLL

此错误发生在这一行：

item.test.Add(model)

你看，它放进了变量，但是当我把模型添加到列表中时，它说它是空的。如何将模型添加到模型列表中？

谢谢。

编辑：

背景项目：

For Each item In food

            Dim weights = weight.Where(Function(x) x.FW_Food_ID = item.NDB_No)
            ... rest of code already posted above

Answer 1

模型不是空的--您的测试属性是。在任何项的构造函数中，都需要“新建”集合。