c# - WPF XAML 限定属性值导致异常

Question

我有一个 WPF 项目，我在其中使用简单的 GridView 来绑定(bind)到元素。我的一个专栏看起来像这样:

<GridViewColumn x:Key="GvcValue" Header="Value"
                            DisplayMemberBinding="{Binding (cmn:ElementData.Value)}" />

如您所见，这会根据预期类型限定绑定(bind)路径，以便进行更好的重构等。我还有其他几列使用此系统绑定(bind)到相同对象类型的其他属性。它们的定义完全相同，除了属性名称，当然还有键。每当显示 GridView 时，这会立即引发此异常:

Key cannot be null.
Parameter name: key
   at System.Collections.Specialized.ListDictionary.get_Item(Object key)
   at System.Collections.Specialized.HybridDictionary.get_Item(Object key)
   at System.ComponentModel.PropertyChangedEventManager.AddListener(INotifyPropertyChanged source, String propertyName, IWeakEventListener listener, EventHandler`1 handler)
   at System.ComponentModel.PropertyChangedEventManager.AddHandler(INotifyPropertyChanged source, EventHandler`1 handler, String propertyName)
   at MS.Internal.Data.PropertyPathWorker.ReplaceItem(Int32 k, Object newO, Object parent)
   at MS.Internal.Data.PropertyPathWorker.UpdateSourceValueState(Int32 k, ICollectionView collectionView, Object newValue, Boolean isASubPropertyChange)
   at MS.Internal.Data.ClrBindingWorker.AttachDataItem()
   at System.Windows.Data.BindingExpression.Activate(Object item)
   at System.Windows.Data.BindingExpression.AttachToContext(AttachAttempt attempt)
   at System.Windows.Data.BindingExpression.MS.Internal.Data.IDataBindEngineClient.AttachToContext(Boolean lastChance)
   at MS.Internal.Data.DataBindEngine.Task.Run(Boolean lastChance)
   at MS.Internal.Data.DataBindEngine.Run(Object arg)
   at MS.Internal.Data.DataBindEngine.OnLayoutUpdated(Object sender, EventArgs e)
   at System.Windows.ContextLayoutManager.fireLayoutUpdateEvent()
   at System.Windows.ContextLayoutManager.UpdateLayout()
   at System.Windows.ContextLayoutManager.UpdateLayoutCallback(Object arg)
   at System.Windows.Media.MediaContext.InvokeOnRenderCallback.DoWork()
   at System.Windows.Media.MediaContext.FireInvokeOnRenderCallbacks()
   at System.Windows.Media.MediaContext.RenderMessageHandlerCore(Object resizedCompositionTarget)
   at System.Windows.Media.MediaContext.RenderMessageHandler(Object resizedCompositionTarget)
   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.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 MS.Internal.CulturePreservingExecutionContext.Run(CulturePreservingExecutionContext 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 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 TestProject.App.Main()

但是，一旦我将其更改为像这样的简单的非限定字符串绑定(bind):

<GridViewColumn x:Key="GvcValue" Header="Value"
                            DisplayMemberBinding="{Binding Value}" />

它可以正常工作并显示它应该显示的内容。更奇怪的是，我可以让所有其他的都合格，但它仍然有效，只是这个导致了问题。

我想如果需要的话我可以将它保留为字符串绑定(bind)，但我想了解发生了什么，甚至想知道如何弄清楚发生了什么。有谁知道那一列会导致这样的问题吗？

Answer 1

发生此异常是因为您使用的是绑定(bind)路径的速记版本，这在正常情况下有效但在这里失败。

将您的代码替换为:

<GridViewColumn x:Key="GvcValue" Header="Value" 
           DisplayMemberBinding="{Binding path=(cmn:ElementData.Value)}" />