调用目标已抛出LINQ和Exception [英] LINQ and Exception has been thrown by the target of an invocation

问题描述

我有带有linq和SQL CE 4.0的WPF .NET FW4应用程序.我在客户的笔记本上随机收到此错误:

I have WPF .NET FW4 application with linq and SQL CE 4.0. Randomly on customer's notebook I recieving this error:

调用的目标已引发异常.

Exception has been thrown by the target of an invocation.

我已经知道，重要的是内部异常(带有堆栈跟踪):

I already know, that important is Inner exception (with stack trace):

对象引用未设置为对象的实例. 在lambda_method(Closure)

Object reference not set to an instance of an object. at lambda_method(Closure )

代码块:

private void LoadCustomersDetail(CustomersView cw)
    {
        Persons customer = db.Persons.Where(c => c.Person_id == cw.Customer_id).FirstOrDefault();
        reg = new RegistrationWindow(db, customer, false);
        reg.ShowDialog();
        if (reg.DialogResult.Value)
        {
            if (!onlyDebtors)
                LoadCustomers();
            else
                LoadDebtors();
        }
    }

原始异常的堆栈跟踪:

at System.RuntimeMethodHandle._InvokeMethodFast(IRuntimeMethodInfo method, Object target, Object[] arguments, SignatureStruct& sig, MethodAttributes methodAttributes, RuntimeType typeOwner)
   at System.RuntimeMethodHandle.InvokeMethodFast(IRuntimeMethodInfo method, Object target, Object[] arguments, Signature sig, MethodAttributes methodAttributes, RuntimeType typeOwner)
   at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean skipVisibilityChecks)
   at System.Delegate.DynamicInvokeImpl(Object[] args)
   at System.Data.Linq.CommonDataServices.GetKeyFromPredicate(MetaType type, Dictionary`2 keys, Expression mex, Expression vex)
   at System.Data.Linq.CommonDataServices.GetKeysFromPredicate(MetaType type, Dictionary`2 keys, Expression expr)
   at System.Data.Linq.CommonDataServices.GetKeyValues(MetaType type, LambdaExpression predicate)
   at System.Data.Linq.CommonDataServices.GetCachedObject(Expression query)
   at System.Data.Linq.CommonDataServices.GetCachedObject(Expression query)
   at System.Data.Linq.SqlClient.SqlProvider.GetCachedResult(Expression query)
   at System.Data.Linq.SqlClient.SqlProvider.System.Data.Linq.Provider.IProvider.Execute(Expression query)
   at System.Data.Linq.DataQuery`1.System.Linq.IQueryProvider.Execute[S](Expression expression)
   at System.Linq.Queryable.FirstOrDefault[TSource](IQueryable`1 source)
   at ProjectName.Core.ViewWindow.LoadCustomersDetail(CustomersView cw)
   at ProjectName.Core.ViewWindow.dataGridCustomersList_MouseDoubleClick(Object sender, MouseButtonEventArgs e)
   at System.Windows.Input.MouseButtonEventArgs.InvokeEventHandler(Delegate genericHandler, Object genericTarget)
   at System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
   at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
   at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
   at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
   at System.Windows.UIElement.RaiseEvent(RoutedEventArgs e)
   at System.Windows.Controls.Control.OnMouseDoubleClick(MouseButtonEventArgs e)
   at System.Windows.Controls.Control.HandleDoubleClick(Object sender, MouseButtonEventArgs e)
   at System.Windows.Input.MouseButtonEventArgs.InvokeEventHandler(Delegate genericHandler, Object genericTarget)
   at System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
   at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
   at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
   at System.Windows.UIElement.ReRaiseEventAs(DependencyObject sender, RoutedEventArgs args, RoutedEvent newEvent)
   at System.Windows.UIElement.OnMouseDownThunk(Object sender, MouseButtonEventArgs e)
   at System.Windows.Input.MouseButtonEventArgs.InvokeEventHandler(Delegate genericHandler, Object genericTarget)
   at System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
   at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
   at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
   at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
   at System.Windows.UIElement.RaiseTrustedEvent(RoutedEventArgs args)
   at System.Windows.UIElement.RaiseEvent(RoutedEventArgs args, Boolean trusted)
   at System.Windows.Input.InputManager.ProcessStagingArea()
   at System.Windows.Input.InputManager.ProcessInput(InputEventArgs input)
   at System.Windows.Input.InputProviderSite.ReportInput(InputReport inputReport)
   at System.Windows.Interop.HwndMouseInputProvider.ReportInput(IntPtr hwnd, InputMode mode, Int32 timestamp, RawMouseActions actions, Int32 x, Int32 y, Int32 wheel)
   at System.Windows.Interop.HwndMouseInputProvider.FilterMessage(IntPtr hwnd, WindowMessage msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at System.Windows.Interop.HwndSource.InputFilterMessage(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o)
   at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
   at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler)

推荐答案

该异常似乎与Where表达式有关，因此c或cw为空.我建议在方法的开头进行参数检查(如果cw == null则抛出ArgumentNullException). 还要确保Persons集合中不包含任何空值(如果可能的话).

The exception seems to concern the Where-expression, so either c or cw is null. I would recommend an argument check at the beginning of the method (throw ArgumentNullException if cw == null). Also make sure the Persons collection contains no null values (if that is even possible).

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