Can't view my user control in the designer (An Unhandled Exception has occurred)

Question

I'm using VS 2012, looking at some code I wrote some time ago. For some reason I cannot view the XAML in the design view, only the XAML view. I'm getting an error that says, "An Unhandled Exception has occurred". I can compile the solution fine,
but it won't let me view it. I don't know why I can't view it in the designer. Here's the error details:
Microsoft.Expression.DesignHost.Isolation.Remoting.RemoteException
Object reference not set to an instance of an object.
   at System.Windows.StyleHelper.FindNameInTemplateContent(DependencyObject container, String childName, FrameworkTemplate frameworkTemplate)
   at System.Windows.TemplateNameScope.System.Windows.Markup.INameScope.FindName(String name)
   at MS.Internal.Data.ElementObjectRef.GetObject(DependencyObject d, ObjectRefArgs args)
   at MS.Internal.Data.ObjectRef.GetDataObject(DependencyObject d, ObjectRefArgs args)
   at System.Windows.Data.BindingExpression.MS.Internal.Data.IDataBindEngineClient.VerifySourceReference(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.UIElement.UpdateLayout()
   at System.Windows.Interop.HwndSource.SetLayoutSize()
   at System.Windows.Interop.HwndSource.set_RootVisualInternal(Visual value)
   at System.Windows.Interop.HwndSource.set_RootVisual(Visual value)
   at Microsoft.Expression.DesignHost.Isolation.Remoting.RemoteUIElement.<>c__DisplayClass12.<Microsoft.Expression.DesignHost.Isolation.Remoting.IRemoteUIElement.CreateContent>b__11()
   at Microsoft.Expression.DesignHost.Isolation.Remoting.ThreadMarshaler.<>c__DisplayClass16`1.<MarshalIn>b__15()
   at Microsoft.Expression.DesignHost.Isolation.Remoting.STAMarshaler.Call.InvokeWorker()
   at Microsoft.Expression.DesignHost.Isolation.Remoting.STAMarshaler.Call.Invoke(Boolean waitingInExternalCall)
   at Microsoft.Expression.DesignHost.Isolation.Remoting.STAMarshaler.InvokeCall(Call call)
   at Microsoft.Expression.DesignHost.Isolation.Remoting.STAMarshaler.ProcessQueue(CallQueue queue)
   at Microsoft.Expression.DesignHost.Isolation.Remoting.STAMarshaler.ProcessInboundAsyncQueue(Int32 identity)
   at Microsoft.Expression.DesignHost.Isolation.Remoting.STAMarshaler.ProcessMessage(Int32 msg, IntPtr wParam, Boolean elevatedQuery, Boolean& handled)
   at Microsoft.Expression.DesignHost.Isolation.Remoting.STAMarshaler.OnWindowMessage(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at Microsoft.Expression.DesignHost.Isolation.Remoting.MessageOnlyHwndWrapper.WndProc(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 Microsoft.Expression.DesignHost.Isolation.IsolationProcess.RunApplication()
   at Microsoft.Expression.DesignHost.Isolation.IsolationProcess.<>c__DisplayClass2.<Main>b__0()
   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()
Rod

Answer 1

I stopped when I saw stuff about databinding.
I guess your problem is you have code in your constructor.
A prameterless constructor of a view will be called by the designer.
This is probably trying to use things which aren't there at design time.
You can mock them or just exit out the constructor if you're in the designer.
public YourUserControlConstructor()
InitializeComponent();
if (DesignerProperties.GetIsInDesignMode(this)
return;
// Dependent code which produces errors
http://social.technet.microsoft.com/wiki/contents/articles/29874.wpf-tips-designer-detection.aspx
Hope that helps.
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