vb.net 可为空的对象必须有一个值。网络
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Nullable object must have a value. VB.NET
提问by Gcode
I need help. I'm having problem in my program. This is my code on my Business logic layer.
我需要帮助。我的程序有问题。这是我在业务逻辑层上的代码。
Function Load_ItemDetails(ByVal ItemID As String) As Items
Dim objItemEnt As New tblitem
Dim objitem As New Items
Try
Using da = New DataAccess
objItemEnt = da.Load_ItemDetails(ItemID)
With objitem
.ItemCode = objItemEnt.ItemCode
.ItemName = objItemEnt.ItemName
.Description = objItemEnt.Description
.NameofType = objItemEnt.NameofType
.TypeofPricing = objItemEnt.TypeofPricing
.OnStock = objItemEnt.OnStock
.ItemPrice = objItemEnt.ItemPrice
.DateModified = objItemEnt.DateModified
End With
Return objitem
End Using
Catch ex As Exception
Throw
End Try
End Function
This code is for my data access layer.
此代码用于我的数据访问层。
Public Function Load_ItemDetails(ByVal ItemCode As String)
Dim objitem As New tblitem
Try
Using entItem = New DAL.systemdbEntities1
Dim qryUsers = From p In entItem.tblitems
Where p.ItemCode = ItemCode
Select p
Dim luser As List(Of tblitem) = qryUsers.ToList
If luser.Count > 0 Then
Return luser.First
Else
Return objitem
End If
End Using
Catch ex As Exception
Throw
End Try
End Function`
For my Presentation layer:
对于我的表示层：
Private Sub Load_Item_Detail(ByVal ItemCode As String)
objItem = New Items
Using objLogic = New LogicalLayer
objItem = objLogic.Load_ItemDetails(ItemCode)
With objItem
Me.ItemCodetxt.Text = .ItemCode
Me.ItemNametxt.Text = .ItemName
Me.ItemDesctxt.Text = .Description
Me.ItemTypetxt.Text = .NameofType
Me.ItemPricetxt.Text = .TypeofPricing
Me.ItemOnstocktxt.Text = CStr(.OnStock)
Me.ItemPricetxt.Text = CStr(.ItemPrice)
Me.TextBox1.Text = CStr(.DateModified)
Me.ItemCodetxt.Tag = .ItemCode
End With
End Using
End Sub`
and after I run, I get this error Nullable object must have a valuehelp me. I'm stuck. I don't know what to do guys. I new in n tier architecture.
在我跑步后，我得到这个错误Nullable object must have a value帮助。我被困住了。我不知道该怎么办伙计们。我是 n 层架构的新手。
回答by OneFineDay
To access the value of a nullable object you use the .Valueof the object. This nullable object also has a .HasValueboolean you can check before asking for the value. More here: Nullable Types
要访问可为空对象的值，请使用.Value对象的 。这个可为空的对象还有一个.HasValue布尔值，您可以在请求值之前进行检查。更多信息：可空类型
If objItemEnt.OnStock.HasValue Then
.OnStock = objItemEnt.OnStock.Value
End If
