Vb.net LINQ查询中的间歇性错误

我在Winforms应用程序中有以下代码，它是通过

BindingSource

在

DataGridView

中加载和显示数据的代码的一部分

Imports System.Data.Entity
Imports System.Data.SqlClient
Imports System.Threading
Imports System.Threading.Tasks
Imports ForeNET.OrderMatching

Public Class frm_OrderMatching
    Private m_Context As ForeContext
    Private m_CurrentManufacturer As Byte = 0
    Private m_CurrentSeries As String = ""
    Private m_mreSeriesManfSet As ManualResetEvent
    Private m_oc_tDSR As ObjectModel.ObservableCollection(Of tbl_Distribution_Stock_Restriction)
    Private m_tLoadQryDistributionAllOrders As Task
    Private m_tLoadSeriesManufacturer As Task

    Private Sub LoadDistributionStockRestrictionTask()
        Dim STime As DateTime = DateTime.Now, ETime As DateTime
        If Not m_CTS.Token.IsCancellationRequested Then
            DoDBContextAction(DBActivityType.Downloading, TimeSpan.FromSeconds(60), True, {False}, Sub() m_Context.tbl_Distribution_Stock_Restriction.Load())
            Dim Tasks As List(Of Task) = New List(Of Task)
            If m_tLoadQryDistributionAllOrders IsNot Nothing Then Tasks.Add(m_tLoadQryDistributionAllOrders)
            If m_tLoadSeriesManufacturer IsNot Nothing Then Tasks.Add(m_tLoadSeriesManufacturer)
            Task.WaitAll(Tasks.ToArray, m_CTS.Token)
            DoDBContextAction(DBActivityType.Downloading, TimeSpan.FromSeconds(60), False, {True}, Sub() bs_tbl_Distribution_Stock_Restriction.ResetBindings(False))
            m_mreSeriesManfSet.WaitOne(TimeSpan.FromSeconds(60))
            If m_oc_tDSR IsNot Nothing Then RemoveHandler m_oc_tDSR.CollectionChanged, AddressOf m_oc_tDSR_CollectionChanged
            'Debug.Print(m_Context.tbl_Distribution_Stock_Restriction.Local.ToString)
            'Debug.Print(m_CurrentSeries)
            'Debug.Print(m_CurrentManufacturer)
            m_oc_tDSR = New ObjectModel.ObservableCollection(Of tbl_Distribution_Stock_Restriction)(From tDSR As tbl_Distribution_Stock_Restriction In m_Context.tbl_Distribution_Stock_Restriction.Local
                                                                                                    Where (tDSR.AUS_SRS_CD = m_CurrentSeries And tDSR.ManufacturerID = m_CurrentManufacturer)
                                                                                                    Select tDSR)
            DoDBContextAction(DBActivityType.Downloading, TimeSpan.FromSeconds(60), False, {True}, Sub()
                                                                                                       bs_tbl_Distribution_Stock_Restriction.DataSource = m_oc_tDSR
                                                                                                       bs_tbl_Distribution_Stock_Restriction.ResetBindings(False)
                                                                                                   End Sub)
            AddHandler m_oc_tDSR.CollectionChanged, AddressOf m_oc_tDSR_CollectionChanged
        End If
    End Sub

    Private Function DoDBContextAction(ActivityType As DBActivityType, Timeout As TimeSpan?, DoLock As Boolean, DoInvoke() As Boolean, ParamArray Action() As Action)
        Dim Saved As Boolean = False, XLoadingBlocked As Boolean = False
        If DoInvoke.Length <> Action.Length Then
            Throw New ArgumentException("The number of elements in the DoInvoke() and Action() arrays must be the same.", "DoInvoke, Action")
        End If
        Do
            If Not DoLock Then
                For Ctr As Integer = 0 To Action.GetUpperBound(0)
                    If DoInvoke(Ctr) And Me.InvokeRequired Then
                        Me.Invoke(Action(Ctr))
                    Else
                        Action(Ctr)()
                    End If
                Next
                Saved = True
            ElseIf Monitor.TryEnter(m_oDataContextLock, TimeSpan.FromMilliseconds(100)) Then
                If XLoadingBlocked Then
                    ' ...
                    XLoadingBlocked = False
                    ' ...
                End If
                Try
                    For Ctr As Integer = 0 To Action.GetUpperBound(0)
                        If DoInvoke(Ctr) And Me.InvokeRequired Then
                            Me.Invoke(Action(Ctr))
                        Else
                            Action(Ctr)()
                        End If
                    Next
                    Saved = True
                Catch ex As Exception
                    Throw
                Finally
                    Monitor.Exit(m_oDataContextLock)
                End Try
            Else
                If Not XLoadingBlocked Then
                    ' ...
                    XLoadingBlocked = True
                    ' ...
                End If
                Thread.Yield()
            End If
        Loop Until Saved Or (Timeout.HasValue AndAlso DateTime.Now - StartTime > Timeout.Value)
        ' ...
        Return Saved
    End Function

    Private Sub frm_OrderMatching_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
        ' Load Data...
        m_Context = New ForeContext
        With m_Context
            .Database.Log = Sub(S As String) Debug.WriteLine(S)
            .Configuration.LazyLoadingEnabled = False
            Dim ConnStr As String = My.Settings.ConnectionString & ";multipleactiveresultsets=True;App=EntityFramework"
            With .Database.Connection
                If .ConnectionString <> ConnStr Or .State = ConnectionState.Closed Then
                    If .State <> ConnectionState.Closed Then
                        .Close()
                    End If
                    .ConnectionString = ConnStr
                    .Open()
                End If
            End With
        End With
        AddHandler DirectCast(m_Context, Infrastructure.IObjectContextAdapter).ObjectContext.SavingChanges, AddressOf ObjectContext_SavingChanges
        m_CTS = New CancellationTokenSource
        m_tsScheduler = New LimitedConcurrencyReprioritizableTaskScheduler(4)
        m_lTaskList = New List(Of Task)
        m_tLoadManufacturers = New Task(AddressOf LoadManufacturersTask, m_CTS.Token)
        m_tLoadCrossBorder = New Task(AddressOf LoadCrossBorderTask, m_CTS.Token)
        m_tLoadDistributionStockModyrsPermitted = New Task(AddressOf LoadDistributionStockModyrsPermittedTask, m_CTS.Token)
        m_tLoadSeriesManufacturer = New Task(AddressOf LoadSeriesManufacturerTask, m_CTS.Token)
        m_tLoadDistributionOrdersPermittedEvent = New Task(AddressOf LoadDistributionOrdersPermittedEventsTask, m_CTS.Token)
        m_tLoadDistributionStockPermittedEvents = New task(AddressOf LoadDistributionStockPermittedEventsTask, m_CTS.Token)
        m_tLoadLayers = New Task(AddressOf LoadLayersTask, m_CTS.Token)
        m_tLoadDistributionSeriesManufacturersLayers = New Task(AddressOf LoadDistributionSeriesManufacturersLayersTask, m_CTS.Token)
        m_tLoadDistributionOrdersRestriction = New Task(AddressOf LoadDistributionOrdersRestrictionTask, m_CTS.Token)
        m_tLoadDistributionStockRestriction = New Task(AddressOf LoadDistributionStockRestrictionTask, m_CTS.Token)
        m_tLoadFAWModel = New Task(AddressOf LoadFAWModelTask, m_CTS.Token)
        m_tLoadPrimaryDealerGroup = New Task(AddressOf LoadPrimaryDealerGroupTask, m_CTS.Token)
        m_tLoadModelCodes = New Task(AddressOf LoadModelCodesTask, m_CTS.Token)
        m_tLoadMatchedOrdersTask = New Task(AddressOf LoadMatchedOrdersTask, m_CTS.Token)
        m_tChangeDMOAFilterTask = Task.Factory.ContinueWhenAll({m_tLoadSeriesManufacturer, m_tLoadPrimaryDealerGroup}, AddressOf ChangeDMOAFilterTask, m_CTS.Token, TaskContinuationOptions.None, m_tsScheduler)
        m_tChangeFMFilterTask = Task.Factory.ContinueWhenAll({m_tLoadSeriesManufacturer, m_tLoadFAWModel, m_tLoadModelCodes}, AddressOf ChangeFMFilterTask, m_CTS.Token, TaskContinuationOptions.None, m_tsScheduler)
        m_lTaskList.AddRange({m_tLoadLayers, m_tLoadManufacturers, m_tLoadCrossBorder, m_tLoadSeriesManufacturer, m_tLoadDistributionOrdersPermittedEvent, m_tLoadDistributionStockPermittedEvents, m_tLoadFAWModel, m_tLoadDistributionStockModyrsPermitted, _
                              m_tLoadDistributionOrdersRestriction, m_tLoadDistributionStockRestriction, m_tLoadPrimaryDealerGroup, m_tLoadModelCodes, m_tLoadMatchedOrdersTask, m_tChangeFMFilterTask})
        m_tLoadComplete = Task.Factory.ContinueWhenAll(m_lTaskList.ToArray, AddressOf LoadCompleteTask, m_CTS.Token, TaskContinuationOptions.None, m_tsScheduler)

        m_tLoadManufacturers.Start(m_tsScheduler)
        m_tLoadCrossBorder.Start(m_tsScheduler)
        m_tLoadDistributionStockModyrsPermitted.Start(m_tsScheduler)
        m_tLoadSeriesManufacturer.Start(m_tsScheduler)
        m_tLoadDistributionOrdersPermittedEvent.Start(m_tsScheduler)
        m_tLoadDistributionStockPermittedEvents.Start(m_tsScheduler)
        m_tLoadLayers.Start(m_tsScheduler)
        m_tLoadDistributionSeriesManufacturersLayers.Start(m_tsScheduler)
        m_tLoadDistributionOrdersRestriction.Start(m_tsScheduler)
        m_tLoadDistributionStockRestriction.Start(m_tsScheduler)
        m_tLoadFAWModel.Start(m_tsScheduler)
        m_tLoadPrimaryDealerGroup.Start(m_tsScheduler)
        m_tLoadModelCodes.Start(m_tsScheduler)
        m_tLoadMatchedOrdersTask.Start(m_tsScheduler)
    End Sub
End Class

LoadDistributionStockRestrictionTask

中的行

Task.WaitAll（Tasks.ToArray，m_CTS.Token）

确保加载依赖实体完成，并且

m_Context.tbl_Distribution_Stock_Restriction.Local

、

m_CurrentSeries

和

m_CurrentManufacturer

具有有效值。有问题的行上方的Debug.Print行表明，发生此错误时总是这样

---

谁能提出一个解决方案。

在哪里可以实例化

m_上下文

呢？顺便说一句，你的VB.Net很难阅读。换行符是你的朋友。根据微软的.Net编码惯例，匈牙利符号不是。@DouglasBarbin，我添加了代码来显示

m_Context

被实例化的位置。很抱歉没有可读性。当你设置断点时，什么是null（“Nothing”）？@DouglasBarbin，我不知道如何准确地找出什么变量是意外的

Nothing

。如果我跳过一步或进入LINQ，那么错误永远不会发生。即使出现错误，上述三条

Debug.Print

语句始终会导致输出正确的值（即not

Nothing

）。如果我没有单步执行，那么我就无法检查内部LINQ变量。

   at System.Data.Entity.Core.Objects.ObjectStateManager.PerformAdd(IList`1 entries)
   at System.Data.Entity.Core.Objects.ObjectStateManager.AlignChangesInRelationships(IList`1 entries)
   at System.Data.Entity.Core.Objects.ObjectStateManager.DetectChanges()
   at System.Data.Entity.Core.Objects.ObjectContext.DetectChanges()
   at System.Data.Entity.Internal.InternalContext.DetectChanges(Boolean force)
   at System.Data.Entity.Internal.Linq.InternalSet`1.get_Local()
   at System.Data.Entity.DbSet`1.get_Local()
   at ForeNET.frm_OrderMatching.LoadDistributionStockRestrictionTask() in C:\Users\jzg48k\Documents\Visual Studio 2010\Projects\Fore GUI\Fore .NET\Forms\frm_OrderMatching.vb:line 1450
   at System.Threading.Tasks.Task.InnerInvoke()
   at System.Threading.Tasks.Task.Execute()