c# - 从 ScatterViewItem 中删除阴影不起作用

Question

我总是使用这段代码从 ScatterViewItem 中移除阴影:

 ScatterViewItem svi = new ScatterViewItem();
 svi.ApplyTemplate();
 svi.Background = new SolidColorBrush(Colors.Transparent);
 svi.ShowsActivationEffects = false;
 svi.BorderBrush = System.Windows.Media.Brushes.Transparent;
 Microsoft.Surface.Presentation.Generic.SurfaceShadowChrome ssc;
 ssc = svi.Template.FindName("shadow", svi) as Microsoft.Surface.Presentation.Generic.SurfaceShadowChrome;
 ssc.Visibility = Visibility.Hidden;

但最近这不再有效了。我总是得到这个异常(exception):

System.NullReferenceException was unhandled
  Message=Object reference not set to an instance of an object.
  Source=Prototype_Concept_2
  StackTrace:
       at Prototype_Concept_2.PackageView.expand(Package pck) in C:\Users\Roflcoptr\Documents\Visual Studio 2008\Projects\Prototype_Concept_2\Prototype_Concept_2\PackageView.xaml.cs:line 45
       at Prototype_Concept_2.PackageView..ctor(SourceFile focus) in C:\Users\Roflcoptr\Documents\Visual Studio 2008\Projects\Prototype_Concept_2\Prototype_Concept_2\PackageView.xaml.cs:line 31
       at Prototype_Concept_2.DetailChooser.ShowPackage_PreviewContactDown(Object sender, ContactEventArgs e) in C:\Users\Roflcoptr\Documents\Visual Studio 2008\Projects\Prototype_Concept_2\Prototype_Concept_2\DetailChooser.xaml.cs:line 213
       at Microsoft.Surface.Presentation.ContactEventArgs.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 args, Boolean trusted)
       at System.Windows.Input.InputManager.ProcessStagingArea()
       at System.Windows.Input.InputManager.ProcessInput(InputEventArgs input)
       at Microsoft.Surface.Presentation.InputSurfaceProviderBase.DoProcessInput(Object obj)
       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: 

这意味着在行 ssc = svi.Template.FindName("shadow", svi) as Microsoft.Surface.Presentation.Generic.SurfaceShadowChrome;必须有一个 NullReference，但我不知道为什么。

Answer 1

问题是 ApplyTemplate 返回 false，因此未应用模板，这意味着它为空。这解释了 NullReferenceException。您可以做的是附加一个事件处理程序，该事件处理程序订阅 ScatterViewItem 的 Loaded 事件，并在处理程序中执行相同的操作。在 WPF 中，模板总是在 Loaded 事件发生时应用

ScatterViewItem svi = new ScatterViewItem();
svi.Background = new SolidColorBrush(Colors.Transparent);
svi.ShowsActivationEffects = false;
svi.BorderBrush = System.Windows.Media.Brushes.Transparent;

RoutedEventHandler loadedEventHandler = null;
loadedEventHandler = new RoutedEventHandler(delegate
{
    svi.Loaded -= loadedEventHandler;
    Microsoft.Surface.Presentation.Generic.SurfaceShadowChrome ssc;
    ssc = svi.Template.FindName("shadow", svi) as Microsoft.Surface.Presentation.Generic.SurfaceShadowChrome;
    ssc.Visibility = Visibility.Hidden;
});
svi.Loaded += loadedEventHandler;