Question

我有一个wpf桌面应用程序，当应该只有一个实例时，我的几个视图被实例化两次。我之所以知道这是因为我使用Visual Studio 2015诊断工具来查看堆。在我看到我的视图有两个实例后，我在其中一个视图的构造函数中放置了一个断点，以查看实际上构造函数是否被调用了两次。它是。每次遇到断点时，我都会查看调用堆栈，看看我的哪些现有对象可能正在构建视图两次，但堆栈只显示堆栈中每个帧中的外部代码。这是第一次在构造函数中的堆栈：

MyApp.exe!MyApp.Views.LineItemView.LineItemView() Line 26   C#
[Native to Managed Transition]  
[Managed to Native Transition]  
mscorlib.dll!System.RuntimeType.CreateInstanceSlow(bool publicOnly, bool skipCheckThis, bool fillCache, ref System.Threading.StackCrawlMark stackMark)  Unknown
mscorlib.dll!System.Activator.CreateInstance(System.Type type, bool nonPublic)  Unknown
mscorlib.dll!System.RuntimeType.CreateInstanceImpl(System.Reflection.BindingFlags bindingAttr, System.Reflection.Binder binder, object[] args, System.Globalization.CultureInfo culture, object[] activationAttributes, ref System.Threading.StackCrawlMark stackMark)  Unknown
mscorlib.dll!System.Activator.CreateInstance(System.Type type, System.Reflection.BindingFlags bindingAttr, System.Reflection.Binder binder, object[] args, System.Globalization.CultureInfo culture, object[] activationAttributes) Unknown
mscorlib.dll!System.Activator.CreateInstance(System.Type type, object[] args)   Unknown
System.Xaml.dll!System.Xaml.Schema.SafeReflectionInvoker.CreateInstanceCritical(System.Type type, object[] arguments)   Unknown
System.Xaml.dll!System.Xaml.Schema.SafeReflectionInvoker.CreateInstance(System.Type type, object[] arguments)   Unknown
System.Xaml.dll!System.Xaml.Schema.XamlTypeInvoker.CreateInstance(object[] arguments)   Unknown
System.Xaml.dll!MS.Internal.Xaml.Runtime.ClrObjectRuntime.CreateInstanceWithCtor(System.Xaml.XamlType xamlType, object[] args)  Unknown
System.Xaml.dll!MS.Internal.Xaml.Runtime.ClrObjectRuntime.CreateInstance(System.Xaml.XamlType xamlType, object[] args)  Unknown
System.Xaml.dll!MS.Internal.Xaml.Runtime.PartialTrustTolerantRuntime.CreateInstance(System.Xaml.XamlType xamlType, object[] args)   Unknown
System.Xaml.dll!System.Xaml.XamlObjectWriter.Logic_CreateAndAssignToParentStart(MS.Internal.Xaml.Context.ObjectWriterContext ctx)   Unknown
System.Xaml.dll!System.Xaml.XamlObjectWriter.WriteEndObject()   Unknown
System.Xaml.dll!System.Xaml.XamlWriter.WriteNode(System.Xaml.XamlReader reader) Unknown
PresentationFramework.dll!System.Windows.FrameworkTemplate.LoadTemplateXaml(System.Xaml.XamlReader templateReader, System.Xaml.XamlObjectWriter currentWriter) Line 1024    C#
PresentationFramework.dll!System.Windows.FrameworkTemplate.LoadTemplateXaml(System.Xaml.XamlObjectWriter objectWriter) Line 982 C#
PresentationFramework.dll!System.Windows.FrameworkTemplate.LoadOptimizedTemplateContent(System.Windows.DependencyObject container, System.Windows.Markup.IComponentConnector componentConnector, System.Windows.Markup.IStyleConnector styleConnector, System.Collections.Generic.List<System.Windows.DependencyObject> affectedChildren, System.Windows.UncommonField<System.Collections.Hashtable> templatedNonFeChildrenField) Line 955  C#
PresentationFramework.dll!System.Windows.FrameworkTemplate.LoadContent(System.Windows.DependencyObject container, System.Collections.Generic.List<System.Windows.DependencyObject> affectedChildren) Line 582   C#
PresentationFramework.dll!System.Windows.StyleHelper.ApplyTemplateContent(System.Windows.UncommonField<System.Collections.Specialized.HybridDictionary[]> dataField, System.Windows.DependencyObject container, System.Windows.FrameworkElementFactory templateRoot, int lastChildIndex, System.Collections.Specialized.HybridDictionary childIndexFromChildID, System.Windows.FrameworkTemplate frameworkTemplate) Line 1869   C#
PresentationFramework.dll!System.Windows.FrameworkTemplate.ApplyTemplateContent(System.Windows.UncommonField<System.Collections.Specialized.HybridDictionary[]> templateDataField, System.Windows.FrameworkElement container) Line 502  C#
PresentationFramework.dll!System.Windows.FrameworkElement.ApplyTemplate() Line 365  C#
PresentationFramework.dll!System.Windows.FrameworkElement.MeasureCore(System.Windows.Size availableSize) Line 4280  C#
PresentationCore.dll!System.Windows.UIElement.Measure(System.Windows.Size availableSize) Line 664   C#
PresentationCore.dll!System.Windows.ContextLayoutManager.UpdateLayout() Line 317    C#
PresentationCore.dll!System.Windows.ContextLayoutManager.UpdateLayoutCallback(object arg) Line 589  C#
PresentationCore.dll!System.Windows.Media.MediaContext.InvokeOnRenderCallback.DoWork() Line 1562    C#
PresentationCore.dll!System.Windows.Media.MediaContext.FireInvokeOnRenderCallbacks() Line 1949  C#
PresentationCore.dll!System.Windows.Media.MediaContext.RenderMessageHandlerCore(object resizedCompositionTarget) Line 1826  C#
PresentationCore.dll!System.Windows.Media.MediaContext.RenderMessageHandler(object resizedCompositionTarget) Line 1721  C#
WindowsBase.dll!System.Windows.Threading.ExceptionWrapper.InternalRealCall(System.Delegate callback, object args, int numArgs)  Unknown
WindowsBase.dll!System.Windows.Threading.ExceptionWrapper.TryCatchWhen(object source, System.Delegate callback, object args, int numArgs, System.Delegate catchHandler) Unknown
WindowsBase.dll!System.Windows.Threading.DispatcherOperation.InvokeImpl()   Unknown
WindowsBase.dll!System.Windows.Threading.DispatcherOperation.InvokeInSecurityContext(object state)  Unknown
mscorlib.dll!System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state, bool preserveSyncCtx)   Unknown
mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state, bool preserveSyncCtx)   Unknown
mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state) Unknown
WindowsBase.dll!System.Windows.Threading.DispatcherOperation.Invoke()   Unknown
WindowsBase.dll!System.Windows.Threading.Dispatcher.ProcessQueue()  Unknown
WindowsBase.dll!System.Windows.Threading.Dispatcher.WndProcHook(System.IntPtr hwnd, int msg, System.IntPtr wParam, System.IntPtr lParam, ref bool handled)  Unknown
WindowsBase.dll!MS.Win32.HwndWrapper.WndProc(System.IntPtr hwnd, int msg, System.IntPtr wParam, System.IntPtr lParam, ref bool handled) Unknown
WindowsBase.dll!MS.Win32.HwndSubclass.DispatcherCallbackOperation(object o) Unknown
WindowsBase.dll!System.Windows.Threading.ExceptionWrapper.InternalRealCall(System.Delegate callback, object args, int numArgs)  Unknown
WindowsBase.dll!System.Windows.Threading.ExceptionWrapper.TryCatchWhen(object source, System.Delegate callback, object args, int numArgs, System.Delegate catchHandler) Unknown
WindowsBase.dll!System.Windows.Threading.Dispatcher.LegacyInvokeImpl(System.Windows.Threading.DispatcherPriority priority, System.TimeSpan timeout, System.Delegate method, object args, int numArgs)   Unknown
WindowsBase.dll!MS.Win32.HwndSubclass.SubclassWndProc(System.IntPtr hwnd, int msg, System.IntPtr wParam, System.IntPtr lParam)  Unknown
[Native to Managed Transition]  
[Managed to Native Transition]  
WindowsBase.dll!System.Windows.Threading.Dispatcher.PushFrameImpl(System.Windows.Threading.DispatcherFrame frame)   Unknown
WindowsBase.dll!System.Windows.Threading.Dispatcher.PushFrame(System.Windows.Threading.DispatcherFrame frame)   Unknown
PresentationFramework.dll!System.Windows.Application.RunDispatcher(object ignore) Line 2756 C#
PresentationFramework.dll!System.Windows.Application.RunInternal(System.Windows.Window window) Line 1845    C#
PresentationFramework.dll!System.Windows.Application.Run(System.Windows.Window window) Line 261 C#
MyApp.exe!MyApp.Program.Main() Line 75  C#

第二次在构造函数中：

MyApp.exe!MyApp.Views.LineItemView.LineItemView() Line 26   C#
    mscorlib.dll!System.Activator.CreateInstance(System.Type type, bool nonPublic)  Unknown
    mscorlib.dll!System.RuntimeType.CreateInstanceImpl(System.Reflection.BindingFlags bindingAttr, System.Reflection.Binder binder, object[] args, System.Globalization.CultureInfo culture, object[] activationAttributes, ref System.Threading.StackCrawlMark stackMark)  Unknown
    mscorlib.dll!System.Activator.CreateInstance(System.Type type, System.Reflection.BindingFlags bindingAttr, System.Reflection.Binder binder, object[] args, System.Globalization.CultureInfo culture, object[] activationAttributes) Unknown
    mscorlib.dll!System.Activator.CreateInstance(System.Type type, object[] args)   Unknown
    System.Xaml.dll!System.Xaml.Schema.SafeReflectionInvoker.CreateInstanceCritical(System.Type type, object[] arguments)   Unknown
    System.Xaml.dll!System.Xaml.Schema.SafeReflectionInvoker.CreateInstance(System.Type type, object[] arguments)   Unknown
    System.Xaml.dll!System.Xaml.Schema.XamlTypeInvoker.CreateInstance(object[] arguments)   Unknown
    System.Xaml.dll!MS.Internal.Xaml.Runtime.ClrObjectRuntime.CreateInstanceWithCtor(System.Xaml.XamlType xamlType, object[] args)  Unknown
    System.Xaml.dll!MS.Internal.Xaml.Runtime.ClrObjectRuntime.CreateInstance(System.Xaml.XamlType xamlType, object[] args)  Unknown
    System.Xaml.dll!MS.Internal.Xaml.Runtime.PartialTrustTolerantRuntime.CreateInstance(System.Xaml.XamlType xamlType, object[] args)   Unknown
    System.Xaml.dll!System.Xaml.XamlObjectWriter.Logic_CreateAndAssignToParentStart(MS.Internal.Xaml.Context.ObjectWriterContext ctx)   Unknown
    System.Xaml.dll!System.Xaml.XamlObjectWriter.WriteEndObject()   Unknown
    System.Xaml.dll!System.Xaml.XamlWriter.WriteNode(System.Xaml.XamlReader reader) Unknown
    PresentationFramework.dll!System.Windows.FrameworkTemplate.LoadTemplateXaml(System.Xaml.XamlReader templateReader, System.Xaml.XamlObjectWriter currentWriter) Line 1024    C#
    PresentationFramework.dll!System.Windows.FrameworkTemplate.LoadTemplateXaml(System.Xaml.XamlObjectWriter objectWriter) Line 982 C#
    PresentationFramework.dll!System.Windows.FrameworkTemplate.LoadOptimizedTemplateContent(System.Windows.DependencyObject container, System.Windows.Markup.IComponentConnector componentConnector, System.Windows.Markup.IStyleConnector styleConnector, System.Collections.Generic.List<System.Windows.DependencyObject> affectedChildren, System.Windows.UncommonField<System.Collections.Hashtable> templatedNonFeChildrenField) Line 955  C#
    PresentationFramework.dll!System.Windows.FrameworkTemplate.LoadContent(System.Windows.DependencyObject container, System.Collections.Generic.List<System.Windows.DependencyObject> affectedChildren) Line 582   C#
    PresentationFramework.dll!System.Windows.StyleHelper.ApplyTemplateContent(System.Windows.UncommonField<System.Collections.Specialized.HybridDictionary[]> dataField, System.Windows.DependencyObject container, System.Windows.FrameworkElementFactory templateRoot, int lastChildIndex, System.Collections.Specialized.HybridDictionary childIndexFromChildID, System.Windows.FrameworkTemplate frameworkTemplate) Line 1869   C#
    PresentationFramework.dll!System.Windows.FrameworkTemplate.ApplyTemplateContent(System.Windows.UncommonField<System.Collections.Specialized.HybridDictionary[]> templateDataField, System.Windows.FrameworkElement container) Line 502  C#
    PresentationFramework.dll!System.Windows.FrameworkElement.ApplyTemplate() Line 365  C#
    PresentationFramework.dll!System.Windows.FrameworkElement.MeasureCore(System.Windows.Size availableSize) Line 4280  C#
    PresentationCore.dll!System.Windows.UIElement.Measure(System.Windows.Size availableSize) Line 664   C#
    PresentationCore.dll!System.Windows.ContextLayoutManager.UpdateLayout() Line 317    C#
    PresentationCore.dll!System.Windows.ContextLayoutManager.UpdateLayoutCallback(object arg) Line 589  C#
    PresentationCore.dll!System.Windows.Media.MediaContext.InvokeOnRenderCallback.DoWork() Line 1562    C#
    PresentationCore.dll!System.Windows.Media.MediaContext.FireInvokeOnRenderCallbacks() Line 1949  C#
    PresentationCore.dll!System.Windows.Media.MediaContext.RenderMessageHandlerCore(object resizedCompositionTarget) Line 1826  C#
    PresentationCore.dll!System.Windows.Media.MediaContext.RenderMessageHandler(object resizedCompositionTarget) Line 1721  C#
    WindowsBase.dll!System.Windows.Threading.ExceptionWrapper.InternalRealCall(System.Delegate callback, object args, int numArgs)  Unknown
    WindowsBase.dll!System.Windows.Threading.ExceptionWrapper.TryCatchWhen(object source, System.Delegate callback, object args, int numArgs, System.Delegate catchHandler) Unknown
    WindowsBase.dll!System.Windows.Threading.DispatcherOperation.InvokeImpl()   Unknown
    WindowsBase.dll!System.Windows.Threading.DispatcherOperation.InvokeInSecurityContext(object state)  Unknown
    mscorlib.dll!System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state, bool preserveSyncCtx)   Unknown
    mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state, bool preserveSyncCtx)   Unknown
    mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state) Unknown
    WindowsBase.dll!System.Windows.Threading.DispatcherOperation.Invoke()   Unknown
    WindowsBase.dll!System.Windows.Threading.Dispatcher.ProcessQueue()  Unknown
    WindowsBase.dll!System.Windows.Threading.Dispatcher.WndProcHook(System.IntPtr hwnd, int msg, System.IntPtr wParam, System.IntPtr lParam, ref bool handled)  Unknown
    WindowsBase.dll!MS.Win32.HwndWrapper.WndProc(System.IntPtr hwnd, int msg, System.IntPtr wParam, System.IntPtr lParam, ref bool handled) Unknown
    WindowsBase.dll!MS.Win32.HwndSubclass.DispatcherCallbackOperation(object o) Unknown
    WindowsBase.dll!System.Windows.Threading.ExceptionWrapper.InternalRealCall(System.Delegate callback, object args, int numArgs)  Unknown
    WindowsBase.dll!System.Windows.Threading.ExceptionWrapper.TryCatchWhen(object source, System.Delegate callback, object args, int numArgs, System.Delegate catchHandler) Unknown
    WindowsBase.dll!System.Windows.Threading.Dispatcher.LegacyInvokeImpl(System.Windows.Threading.DispatcherPriority priority, System.TimeSpan timeout, System.Delegate method, object args, int numArgs)   Unknown
    WindowsBase.dll!MS.Win32.HwndSubclass.SubclassWndProc(System.IntPtr hwnd, int msg, System.IntPtr wParam, System.IntPtr lParam)  Unknown
    [Native to Managed Transition]  
    [Managed to Native Transition]  
    WindowsBase.dll!System.Windows.Threading.Dispatcher.PushFrameImpl(System.Windows.Threading.DispatcherFrame frame)   Unknown
    WindowsBase.dll!System.Windows.Threading.Dispatcher.PushFrame(System.Windows.Threading.DispatcherFrame frame)   Unknown
    PresentationFramework.dll!System.Windows.Application.RunDispatcher(object ignore) Line 2756 C#
    PresentationFramework.dll!System.Windows.Application.RunInternal(System.Windows.Window window) Line 1845    C#
    PresentationFramework.dll!System.Windows.Application.Run(System.Windows.Window window) Line 261 C#
    MyApp.exe!MyApp.Program.Main() Line 75  C#

有关如何调试此问题的任何想法？

Answer 1

无法根据信息调试，但我之前遇到过这样的问题。这是因为我对DataContext有一个绑定，但我在App.xaml上也有它DataTemplate'd，因此ViewModel也会调用该视图。由于我绝对需要XAML绑定和DataTemplates，我只是编写了一个解决方法来处理对构造函数的两次调用。

也许你有类似的东西？

Answer 2

从您的班级LineItemView的名称来看，您听到的内容更多。您需要为此提供更多上下文，因为上面没有足够的信息。要调试它，请检查项目的DataContext（虽然在构造函数中不可用），以查看导致构造的原因。您还可以查看Parent属性。在这两方面，您都需要连接OnVisualParentChanged或OnInitialized方法。

在这样的时候，仅使用相关代码创建一个新的独立项目并查看问题是否仍然存在也是有用的。

Answer 3

我认为在Xaml中，可能会将dataconext设置两次，或者可能绑定两次，如果你附加Xaml会更好，这样我就可以识别。

为什么视图构造函数被调用两次？

3 个答案: