Problem with Animation if ScatterViewItem changes its size

My idea was to set the content of my ScatterViewItem depending on its size. So I wrote a piece of code that calls a storyboard so that the content is set dependeing on the size of the ScatterViewItem:

 private void Package_ContactDown(object sender, ContactEventArgs e)
        {
            ScatterViewItem svi = new ScatterViewItem();
            svi.Orientation = 0;
            removeShadow(svi);
            svi.IsActive = true;
            PackageView view = new PackageView(sourceFile, this);
            view.setScatterViewItem(svi);
            svi.Width = 1024;
            svi.Height = 768;
            svi.Center = new Point(512, 384);
            Viewbox box = new Viewbox();
            box.Child = view;

            Viewbox boxSmall = new Viewbox();
            boxSmall.Name = "SmallLayout";
            TextBlock txt = new TextBlock();
            txt.Text = "Package of class";
            boxSmall.Child = txt;
            boxSmall.Visibility = System.Windows.Visibility.Collapsed;
            boxSmall.Opacity = 0;
            boxSmall.IsHitTestVisible = false;

            Grid g = new Grid();
            g.Children.Add(box);
            g.Children.Add(boxSmall);
            svi.Content = g;

            window.IconDisplay.Items.Add(svi);

            DoubleAnimation animation = new DoubleAnimation();
            animation.From = 0.0;
            animation.To = 1.0;
            animation.Duration = new Duration(TimeSpan.FromSeconds(3));
            animation.AutoReverse = false;

            Storyboard storyboard = new Storyboard();
            storyboard.Children.Add(animation);
            Storyboard.SetTargetName(animation, boxSmall.Name);
            Storyboard.SetTargetProperty(animation, new PropertyPath(Viewbox.OpacityProperty));

            svi.SizeChanged += delegate(object s, SizeChangedEventArgs args)
            {
                if (args.NewSize.Width < 150 && args.NewSize.Height < 150)
             开发者_如何学JAVA   {
                    boxSmall.Visibility = System.Windows.Visibility.Visible;
                    box.Visibility = System.Windows.Visibility.Collapsed;
                    storyboard.Begin(this);
                }
            };

        }

Unfortunately I alawys get this exception:

System.InvalidOperationException was unhandled
  Message='SmallLayout' name cannot be found in the name scope of 'Prototype_Concept_2.views.DetailChooser'.
  Source=PresentationFramework
  StackTrace:
       at System.Windows.Media.Animation.Storyboard.ResolveTargetName(String targetName, INameScope nameScope, DependencyObject element)
       at System.Windows.Media.Animation.Storyboard.ClockTreeWalkRecursive(Clock currentClock, DependencyObject containingObject, INameScope nameScope, DependencyObject parentObject, String parentObjectName, PropertyPath parentPropertyPath, HandoffBehavior handoffBehavior, HybridDictionary clockMappings, Int64 layer)
       at System.Windows.Media.Animation.Storyboard.ClockTreeWalkRecursive(Clock currentClock, DependencyObject containingObject, INameScope nameScope, DependencyObject parentObject, String parentObjectName, PropertyPath parentPropertyPath, HandoffBehavior handoffBehavior, HybridDictionary clockMappings, Int64 layer)
       at System.Windows.Media.Animation.Storyboard.BeginCommon(DependencyObject containingObject, INameScope nameScope, HandoffBehavior handoffBehavior, Boolean isControllable, Int64 layer)
       at System.Windows.Media.Animation.Storyboard.Begin(FrameworkElement containingObject)
       at Prototype_Concept_2.views.DetailChooser.<>c__DisplayClass1.<Package_ContactDown>b__0(Object s, SizeChangedEventArgs args) in C:\Users\Roflcoptr\Documents\Visual Studio 2008\Projects\Prototype_Concept_2\Prototype_Concept_2\views\DetailChooser.xaml.cs:line 244
       at System.Windows.SizeChangedEventArgs.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.RaiseEvent(RoutedEventArgs e)
       at System.Windows.FrameworkElement.OnRenderSizeChanged(SizeChangedInfo sizeInfo)
       at System.Windows.ContextLayoutManager.fireSizeChangedEvents()
       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, Boolean isSingleParameter)
       at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Boolean isSingleParameter, Delegate catchHandler)
       at System.Windows.Threading.Dispatcher.WrappedInvoke(Delegate callback, Object args, Boolean isSingleParameter, Delegate catchHandler)
       at System.Windows.Threading.DispatcherOperation.InvokeImpl()
       at System.Windows.Threading.DispatcherOperation.InvokeInSecurityContext(Object state)
       at System.Threading.ExecutionContext.runTryCode(Object userData)
       at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData)
       at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
       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, Boolean isSingleParameter)
       at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Boolean isSingleParameter, Delegate catchHandler)
       at System.Windows.Threading.Dispatcher.WrappedInvoke(Delegate callback, Object args, Boolean isSingleParameter, Delegate catchHandler)
       at System.Windows.Threading.Dispatcher.InvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Boolean isSingleParameter)
       at System.Windows.Threading.Dispatcher.Invoke(DispatcherPriority priority, Delegate method, Object arg)
       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 Prototype_Concept_2.App.Main() in C:\Users\Roflcoptr\Documents\Visual Studio 2008\Projects\Prototype_Concept_2\Prototype_Concept_2\obj\Debug\App.g.cs:line 0
       at System.AppDomain._nExecuteAssembly(Assembly 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.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()
  InnerException: 

I don't really understand the problem. Any hints?

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it's saying you dont have a child named SmallLayout inside of the DetailChooser element