使用 XAML 设计器时发生 NullReferenceException

Question

更新到最新版本的 Visual Studio 2015 后，我无法使用 XAML 设计器，因为每次我尝试打开它时都会出现一个屏幕通知我发生了 NullReferenceException。

我已经尝试了下面帖子中详细介绍的解决方案，但是，由于我不是 HP 用户，因此该解决方案对我不起作用。

Visual Studio 2015 (Community) designer shows NullReferenceException for blank Universal App

请参阅下面的附加屏幕截图和错误消息。任何帮助将不胜感激

System.NullReferenceException
Object reference not set to an instance of an object.

Server stack trace: 
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.Primitives.IsolationBoundary.RemoteIsolationContext.<>c__DisplayClass14_0.<Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.Primitives.IsolationBoundary.IRemoteContext.CreateInstance>b__0()
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.Remoting.ThreadMarshaler.<>c__DisplayClass47_0`1.<MarshalIn>b__0()
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.Remoting.STAMarshaler.Call.InvokeWorker()
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.Remoting.STAMarshaler.Call.Invoke(Boolean waitingInExternalCall)
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.Remoting.STAMarshaler.InvokeCall(Call call)
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.Remoting.STAMarshaler.DirectInvoke(Boolean inbound, Action action, Int32 sourceApartmentId, Int32 targetApartmentId, Int32 originId, WaitHandle aborted)
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.Remoting.STAMarshaler.DirectInvokeInbound(Action action, Int32 targetApartmentId)
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.Remoting.STAMarshaler.MarshalIn(Action action, Int32 targetApartmentId, CancellationToken cancelToken, CallSynchronizationMode syncMode, CallModality callModality, String methodName, String filePath, Int32 lineNumber)
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.Remoting.ThreadMarshaler.MarshalIn(IRemoteObject targetObject, Action action, CallSynchronizationMode syncMode, CallModality callModality, ApartmentState apartmentState, String memberName, String filePath, Int32 lineNumber)
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.Remoting.ThreadMarshaler.MarshalIn[TResult](IRemoteObject targetObject, Func`1 func, CallModality callModality, ApartmentState apartmentState, String memberName, String filePath, Int32 lineNumber)
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.Primitives.IsolationBoundary.RemoteIsolationContext.Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.Primitives.IsolationBoundary.IRemoteContext.CreateInstance(String assemblyName, String assemblyCodeBase, String typeName)
   at System.Runtime.Remoting.Messaging.StackBuilderSink._PrivateProcessMessage(IntPtr md, Object[] args, Object server, Object[]& outArgs)
   at System.Runtime.Remoting.Messaging.StackBuilderSink.SyncProcessMessage(IMessage msg)

Exception rethrown at [0]: 
   at System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg, IMessage retMsg)
   at System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgData, Int32 type)
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.Primitives.IsolationBoundary.IRemoteContext.CreateInstance(String assemblyName, String assemblyCodeBase, String typeName)
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.Primitives.IsolationBoundary.<>c__DisplayClass38_0`1.<CreateInstance>b__0(IRemoteContext c)
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.Remoting.ThreadMarshaler.<>c__DisplayClass31_0`2.<MarshalOut>b__0()
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.Remoting.STAMarshaler.Call.InvokeWorker()

System.NullReferenceException
Object reference not set to an instance of an object.
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.Remoting.STAMarshaler.WaitForCompletion(NestedCallContext nestedCallContext, BlockingCall call, WaitHandle timeoutSignal)
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.Remoting.STAMarshaler.MarshalOutSynchronous(Action action, Int32 targetApartmentId, WaitHandle aborted, WaitHandle timeoutSignal, CancellationToken cancelToken, String methodName, String filePath, Int32 lineNumber)
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.Remoting.STAMarshaler.MarshalOut(Action action, Int32 targetApartmentId, WaitHandle aborted, CancellationToken cancelToken, CallSynchronizationMode syncMode, WaitHandle timeoutSignal, String methodName, String filePath, Int32 lineNumber)
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.Remoting.ThreadMarshaler.MarshalOut[TValue](RemoteHandle`1 targetObject, Action action, CallSynchronizationMode syncMode, ApartmentState apartmentState, String methodName, String filePath, Int32 lineNumber)
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.Remoting.ThreadMarshaler.MarshalOut[TResult,TValue](RemoteHandle`1 targetObject, Func`2 func, CallSynchronizationMode syncMode, ApartmentState apartmentState, String methodName, String filePath, Int32 lineNumber)
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.Primitives.IsolationBoundary.CreateInstance[T](Type type)
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.IsolatedObjectFactory.Initialize()
   at Microsoft.VisualStudio.DesignTools.DesignerHost.Services.VSIsolationService.CreateObjectFactory(IIsolationTarget isolationTarget, IObjectCatalog catalog)
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.IsolationService.CreateLease(IIsolationTarget isolationTarget)
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.IsolationService.CreateLease(IIsolationTarget isolationTarget)
   at Microsoft.VisualStudio.DesignTools.DesignerContract.IsolatedDesignerService.CreateLease(IIsolationTarget isolationTarget, CancellationToken cancelToken, DesignerServiceEntry& entry, IServiceProvider serviceOverrides)
   at Microsoft.VisualStudio.DesignTools.DesignerContract.IsolatedDesignerService.IsolatedDesignerView.CreateDesignerViewInfo(CancellationToken cancelToken)
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.IsolatedTaskScheduler.InvokeWithCulture[T](CultureInfo culture, Func`2 func, CancellationToken cancelToken)
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.IsolatedTaskScheduler.<>c__DisplayClass10_0`1.<StartTask>b__0()
   at System.Threading.Tasks.Task`1.InnerInvoke()
   at System.Threading.Tasks.Task.Execute()

Answer 1

您将在构造函数中包含一些代码，这些代码依赖于通常仅在运行时设置的内容（例如数据库连接）。

您需要将代码包装在这样的测试中：

if (!Windows.ApplicationModel.DesignMode.DesignModeEnabled)
{
    // Runtime mode specific functionality
}

注意 DesignModeEnabled 属性仅在有开发者证书的情况下可用。

Source

您可以对构造函数中的所有代码执行此操作，也可以尝试缩小范围，以便仅对尽可能少的代码进行测试。或者，您应该考虑将该代码从构造函数中移出到 OnLoaded 事件处理程序中。

Answer 2

同样的事情也发生在我身上。我删除了项目中的.vs、bin、obj 目录，它起作用了。