Question

我有一个对象，我正在尝试使用PropertyGrid，并在尝试访问Color []属性时抛出NullReferenceException。

堆栈跟踪如下所示：

System.NullReferenceException: Object reference not set to an instance of an object.
   at Xceed.Wpf.Toolkit.CollectionControlDialog.Clone(Object source) in C:\Users\brian\Documents\Visual Studio 2015\Projects\FevDnDTester\ExtendedWPFToolkitSolution\Src\Xceed.Wpf.Toolkit\CollectionControl\Implementation\CollectionControlDialog.xaml.cs:line 168
   at Xceed.Wpf.Toolkit.CollectionControlDialog.OnSourceInitialized(EventArgs e) in C:\Users\brian\Documents\Visual Studio 2015\Projects\FevDnDTester\ExtendedWPFToolkitSolution\Src\Xceed.Wpf.Toolkit\CollectionControl\Implementation\CollectionControlDialog.xaml.cs:line 137
   at System.Windows.Window.CreateSourceWindow(Boolean duringShow)
   at System.Windows.Window.CreateSourceWindowDuringShow()
   at System.Windows.Window.SafeCreateWindowDuringShow()
   at System.Windows.Window.ShowHelper(Object booleanBox)
   at System.Windows.Window.Show()
   at System.Windows.Window.ShowDialog()
   at Xceed.Wpf.Toolkit.CollectionControlButton.CollectionControlButton_Click(Object sender, RoutedEventArgs e) in C:\Users\brian\Documents\Visual Studio 2015\Projects\FevDnDTester\ExtendedWPFToolkitSolution\Src\Xceed.Wpf.Toolkit\CollectionControl\Implementation\CollectionControlButton.cs:line 124
   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.Primitives.ButtonBase.OnClick()
   at System.Windows.Controls.Button.OnClick()
   at System.Windows.Controls.Primitives.ButtonBase.OnMouseLeftButtonUp(MouseButtonEventArgs e)
   at System.Windows.UIElement.OnMouseLeftButtonUpThunk(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.OnMouseUpThunk(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)

正如您所看到的，没有任何与我自己的代码相关的内容，因此这必定是一个相当常见的错误。看起来它正在尝试克隆我的Color对象数组并失败，但是数组中没有任何对象是null。

有什么想法吗？

Answer 1

这是CollectionControlDialog类中的错误。

在方法Clone()中，它们获取所提供的集合项的类型，然后尝试调用该类型的默认构造函数。我想，他们想要创建每个集合项的深层副本。

但显然，struct Color没有默认构造函数（作为方法），可以通过反射获得。（您可以在struct上使用的默认无参数构造函数实际上不是构造函数，但它是运行时如何创建struct的默认实例的IL指令。

这就是为什么GetConstructor()方法返回null，并尝试调用null上的方法会抛出你观察到的NullReferenceException。

您可以自行列出错误或修复它并提交到Xceed存储库。

目前，此错误会阻止您将CollectionControlDialog用于没有默认无参数构造函数的对象（例如struct或某些class）。

带有System.Windows.Media.Color []的Xceed PropertyGrid会抛出NullReferenceException

1 个答案: