C# Property.GetValue-测试是否存在空引用内部异常的空中断？

我需要扫描一堆Outlook“.msg”文件，我正在使用MsgReader库进行扫描。 我编写了下面的方法，它打开消息，读取每个属性，并提取标记为“string”的任何属性，将其添加到字典中以返回给调用方。 代码如下：

    public Dictionary<string, string> GetMsgFileDetails(string filepath)
    {
        Dictionary<string, string> filedetails = new Dictionary<string, string>();
        //try
        {
            string fullpath = Path.Combine(SelectedFolder, filepath);
            var msg = new Storage.Message(fullpath);
            foreach (var prop in msg.GetType().GetProperties())
            {
                string pname = prop.Name;

                if (prop.GetValue(msg) != null)
                {
                    object pvalue = prop.GetValue(msg);
                }
                // We only want the strings
                if (prop.GetValue(msg) != null && (prop.GetValue(msg) is string))
                {
                    filedetails.Add(prop.Name, prop.GetValue(msg).ToString());
                }

            }
            return filedetails;
        }
        //catch (Exception ex)
        //{
        //    MessageBox.Show(ex.Message, "Error trying to load file");
        //    return null;
        //}
    }

 (the try-catch block is commented out to allow easier debugging).

要与系统反射TargetInException断开的行。例外情况详情如下：

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这似乎是由于prop.GetValue的值计算为null，但这正是我要测试的。 我意识到这可能是深入思考，我不是一个专家，所以如果有人有任何想法如何做这个检查，我真的很感激。

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干杯。

我将此标记为一个答案，以防其他人遇到相同的问题。MsgReader库中确实存在一个bug。我已经在那里提出了这个问题，并且已经非常友好地提供了一些解决办法。球队也将修复它，所以这只希望是短暂的

您应该尝试获取InnerException的堆栈跟踪。这很可能是MsgReader中的一个bug。您应该能够通过在获取属性之前记录它获取的属性来测试这一点，然后您可以编写相同的代码而不进行反射以查看发生了什么。如果您只需要字符串属性，那么在知道属性是字符串之前，不要调用

GetValue

。您可以使用

prop.PropertyType==typeof（string）

进行检查。好主意，黛西，谢谢。。我确实知道它是哪一个属性，所以我会按照你的建议不加思考地尝试它。谢谢Evk，但碰巧的是，失败的属性类型是字符串。这是MailingListHelp属性。我在foreach语句之前添加了一行：var msgmailhelp=msg.MailingListHelp。它是string类型，如果不存在任何内容，则返回空值。相反，它会因System.NullReferenceException而中断。所以我想我的下一站是GitHub问题部分。。。再次感谢黛西。

   (prop.GetValue(msg) != null)

C:\Users\Brett\source\repos\FileMunger\FileMunger\ViewModels\FolderContext.cs:line 208
at FileThing.ViewModels.FolderContext.GetProperties(String filepath, Boolean showwindow) in C:\Users\Brett\source\repos\FileMunger\FileMunger\ViewModels\FolderContext.cs:line 159
at FileMunger.MainWindow.FileList_Selected(Object sender, RoutedEventArgs e) in C:\Users\Brett\source\repos\FileMunger\FileMunger\MainWindow.xaml.cs:line 121
at system.Windows.Controls.SelectionChangedEventArgs.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.ListBox.OnSelectionChanged(SelectionChangedEventArgs e)
at System.Windows.Controls.Primitives.Selector.InvokeSelectionChanged(List`1 unselectedInfos, List`1 selectedInfos)
at System.Windows.Controls.Primitives.Selector.SelectionChanger.End()
at System.Windows.Controls.Primitives.Selector.SelectionChanger.SelectJustThisItem(ItemInfo info, Boolean assumeInItemsCollection)
at System.Windows.Controls.ListBox.MakeSingleSelection(ListBoxItem listItem)
at System.Windows.Controls.ListBox.NotifyListItemClicked(ListBoxItem item, MouseButton mouseButton)
at System.Windows.Controls.ListBoxItem.HandleMouseButtonDown(MouseButton mouseButton)
at System.Windows.Controls.ListBoxItem.OnMouseLeftButtonDown(MouseButtonEventArgs e)
at System.Windows.UIElement.OnMouseLeftButtonDownThunk(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 System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)
at System.Windows.Threading.Dispatcher.LegacyInvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Int32 numArgs)
at MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam)
at MS.Win32.UnsafeNativeMethods.DispatchMessage(MSG& msg)
at System.Windows.Threading.Dispatcher.PushFrameImpl(DispatcherFrame frame)
at System.Windows.Threading.Dispatcher.PushFrame(DispatcherFrame frame)
at System.Windows.Application.RunDispatcher(Object ignore)
at System.Windows.Application.RunInternal(Window window)
at System.Windows.Application.Run(Window window)
at System.Windows.Application.Run()
at FileMunger.App.Main()

Inner Exception 1:
 NullReferenceException: Object reference not set to an instance of an object.