Question

我正在尝试使用Graph# library for C#加载并显示GraphML文档，并且在一条似乎没有意义的行上获得NullReferenceException：

private void load(string fileName) {
    var graph = new CompoundGraph<object, IEdge<object>>();

    //open the file of the graph
    var reader = XmlReader.Create(fileName);

    //create the serializer
    var serializer = new GraphMLDeserializer<object,
        IEdge<object>,
        CompoundGraph<object, IEdge<object>>>();

    //deserialize the graph
    serializer.Deserialize(reader, graph,
        id => id, (source, target, id) => new Edge<object>(source, target)
        );

    Console.WriteLine(graph);               // okay
    Console.WriteLine(graphLayout.Graph);   // okay

    this.graphLayout.Graph = graph;         // crashes
    this.graphLayout.UpdateLayout();
}

我使用调试器检查了对象值，一切似乎都是有序的。还有什么可能出错？为什么我在已初始化的对象上获得NullReferenceException？

如果您更喜欢浏览整个源代码（或者如果您非常喜欢自己编译;我们非常欢迎您），我一直在GitHub上提供该项目。我添加了a commit来重现问题。

完整堆栈跟踪：

System.NullReferenceException was unhandled
  HResult=-2147467261
  Message=Object reference not set to an instance of an object.
  Source=GraphSharp.Controls
  StackTrace:
       at GraphSharp.Controls.GraphLayout`3.Layout(Boolean continueLayout)
       at GraphSharp.Controls.GraphLayout`3.Relayout()
       at GraphSharp.Controls.GraphLayout`3.OnRelayoutInduction(Boolean tryKeepControls)
       at GraphSharp.Controls.GraphLayout`3.Graph_PropertyChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)
       at System.Windows.DependencyObject.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
       at System.Windows.FrameworkElement.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
       at System.Windows.DependencyObject.NotifyPropertyChange(DependencyPropertyChangedEventArgs args)
       at System.Windows.DependencyObject.UpdateEffectiveValue(EntryIndex entryIndex, DependencyProperty dp, PropertyMetadata metadata, EffectiveValueEntry oldEntry, EffectiveValueEntry& newEntry, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType)
       at System.Windows.DependencyObject.SetValueCommon(DependencyProperty dp, Object value, PropertyMetadata metadata, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType, Boolean isInternal)
       at System.Windows.DependencyObject.SetValue(DependencyProperty dp, Object value)
       at GraphSharp.Controls.GraphLayout`3.set_Graph(TGraph value)
       at SMP.MainWindow.load(String fileName) in t:\#_\Programming\GitHub\SMP\SMP\Simulator.xaml.cs:line 61
       at SMP.MainWindow.Load_GMX_Graph(Object sender, RoutedEventArgs e) in t:\#_\Programming\GitHub\SMP\SMP\Simulator.xaml.cs:line 38
       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.MenuItem.InvokeClickAfterRender(Object arg)
       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)
       at System.Windows.Threading.DispatcherOperation.InvokeImpl()
       at System.Windows.Threading.DispatcherOperation.InvokeInSecurityContext(Object state)
       at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Windows.Threading.DispatcherOperation.Invoke()
       at System.Windows.Threading.Dispatcher.ProcessQueue()
       at System.Windows.Threading.Dispatcher.WndProcHook(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)
       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.Threading.Dispatcher.Run()
       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 SMP.App.Main() in t:\#_\Programming\GitHub\SMP\SMP\obj\Debug\App.g.cs:line 0
       at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
       at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()
  InnerException:

Answer 1

检查第61行的Simulator.xaml.cs文件。在抛出异常之前，你的最后一个代码就在那里......

NullReferenceException on（貌似）完全初始化的对象

1 个答案: