PresentationFramework中的NullReference异常 [英] NullReference Exception in PresentationFramework
问题描述
下面是一个最小的示例，我不可能再减少它了.
Below is a minimal example, I couldn't possibly reduce it any more than this.
我像这样在ViewModel中创建一个实时筛选的CollectionView:
I create a live filtered CollectionView in the ViewModel like this:
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Collections.Specialized;
using System.ComponentModel;
using System.Windows.Data;
using System.Windows;
namespace AntiBonto.ViewModel
{
[Serializable]
public class Person
{
public event PropertyChangedEventHandler PropertyChanged;
protected void RaisePropertyChanged([CallerMemberName] String propertyName = "")
{
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
public string Name { get; set; }
public override string ToString()
{
return Name;
}
private int num;
public int Num
{
get { return num; }
set { num = value; RaisePropertyChanged(); }
}
}
class ObservableCollection2<T> : ObservableCollection<T>
{
public ObservableCollection2() : base() { }
public ObservableCollection2(T[] t) : base(t) { }
public void AddRange(IEnumerable<T> collection)
{
foreach (var i in collection)
{
Items.Add(i);
}
OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
}
}
class MainWindow: ViewModelBase
{
public MainWindow() { }
private ObservableCollection2<Person> people = new ObservableCollection2<Person>();
public ObservableCollection2<Person> People
{
get
{
return people;
}
set
{
people = value;
RaisePropertyChanged();
}
}
public ICollectionView Team
{
get
{
CollectionViewSource cvs = new CollectionViewSource { Source = People, IsLiveFilteringRequested = true, LiveFilteringProperties = { "Num" } };
cvs.View.Filter = p => ((Person)p).Num != 11;
return cvs.View;
}
}
public ICollectionView Ujoncok
{
get
{
CollectionViewSource cvs = new CollectionViewSource { Source = People, IsLiveFilteringRequested = true, LiveFilteringProperties = { "Num" } };
cvs.View.Filter = p => ((Person)p).Num == 11;
return cvs.View;
}
}
}
}
GUI上有一个按钮，用于修改People集合中的Person对象:
The GUI has a button that modifies a Person object in the People collection:
<Window x:Class="AntiBonto.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:vm="clr-namespace:AntiBonto.ViewModel"
mc:Ignorable="d"
Title="AntiBonto" Width="1024" Height="768">
<Window.DataContext>
<vm:MainWindow/>
</Window.DataContext>
<Window.Resources>
<FrameworkElement x:Key="DataContextProxy" DataContext="{Binding}"/> <!-- workaround, see http://stackoverflow.com/questions/7660967 -->
</Window.Resources>
<TabControl>
<TabItem Header="Tab2">
<StackPanel>
<Button Content="Does" Click="Button_Click"/>
<ContentControl Visibility="Collapsed" Content="{StaticResource DataContextProxy}"/>
<!-- workaround part 2 -->
<DataGrid ItemsSource="{Binding Ujoncok}" CanUserAddRows="False" CanUserDeleteRows="False" AutoGenerateColumns="False">
<DataGrid.Columns>
<DataGridComboBoxColumn Header="Who" ItemsSource="{Binding DataContext.Team, Source={StaticResource DataContextProxy}, Mode=OneWay}"/>
</DataGrid.Columns>
</DataGrid>
</StackPanel>
</TabItem>
</TabControl>
</Window>
我从XML文件中加载数据，如下所示:
I load the data from an XML file like this:
using System;
using System.IO;
using System.Linq;
using System.Windows;
using System.Xml.Serialization;
namespace AntiBonto
{
[Serializable]
public class AppData
{
public Person[] Persons;
}
public partial class MainWindow : System.Windows.Window
{
public MainWindow()
{
InitializeComponent();
Loaded += MainWindow_Loaded;
}
private string filepath = "state.xml";
private AppData AppData
{
get { return new AppData { Persons = viewModel.People.ToArray()}; }
set { viewModel.People.AddRange(value.Persons);}
}
private void MainWindow_Loaded(object sender, RoutedEventArgs e)
{
var xs = new XmlSerializer(typeof(AppData));
if (File.Exists(filepath))
{
using (var file = new StreamReader(filepath))
{
AppData = (AppData)xs.Deserialize(file);
}
}
}
private ViewModel.MainWindow viewModel { get { return (ViewModel.MainWindow)DataContext; } }
private void Button_Click(object sender, RoutedEventArgs e)
{
Person p = viewModel.People.First(q => q.Name == "Ferencz Katalin");
if (p.Num == 11)
p.Num = 0;
else
p.Num= 11;
}
}
}
而XML文件是这样的:
and the XML file is this:
<?xml version="1.0" encoding="utf-8"?>
<AppData xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<Persons>
<Person>
<Name>Person1</Name>
<Num>0</Num>
</Person>
<Person>
<Name>Person2</Name>
<Num>0</Num>
</Person>
</Persons>
</AppData>
当我单击按钮一次或两次时，出现一个 NullReference 异常.没有内在的例外.异常不是在我的代码中出现的，而是在框架代码中出现的，因此它没有显示源，我无法找出哪个对象为null以及异常来自何处.我没有设置进入.NET源代码"，它仍然告诉我没有可用的源代码.
When I click the button once or twice, I get a NullReference exception. There is no inner exception. The exception does not arise in my code, but in framework code, so it does not show the source, I cannot find out which object is null and where the exception comes from. I didn't manage to set up "stepping into .NET sources", it still tells me that there is no source available.
这是堆栈跟踪:
在System.Windows.Data.ListCollectionView.RestoreLiveShaping()处的System.Windows.Threading.ExceptionWrapper.InternalRealCall(委托回调，对象args，Int32 numArgs)System.Windows.Threading.ExceptionWrapper.TryCatchWhen(对象源，委托回调，对象args，Int32 numArgs，委托catchHandler)在System.Windows.Threading.DispatcherOperation.InvokeImpl()在System.Windows.Threading.DispatcherOperation.InvokeInSecurityContext(Object州)System.Threading.ExecutionContext.RunInternal(ExecutionContextexecutionContext，ContextCallback回调，对象状态，布尔值reserveSyncCtx)位于System.Threading.ExecutionContext.Run(ExecutionContextexecutionContext，ContextCallback回调，对象状态，布尔值reserveSyncCtx)位于System.Threading.ExecutionContext.Run(ExecutionContextexecutionContext，ContextCallback回调，对象状态)位于MS.Internal.CulturePreservingExecutionContext.Run(CulturePreservingExecutionContextexecutionContext，ContextCallback回调，对象状态)位于System.Windows.Threading.DispatcherOperation.Invoke()在System.Windows.Threading.Dispatcher.ProcessQueue()在System.Windows.Threading.Dispatcher.WndProcHook(IntPtr hwnd，Int32msg，IntPtr wParam，IntPtr lParam，布尔值和处理)MS.Win32.HwndWrapper.WndProc(IntPtr hwnd，Int32 msg，IntPtr wParam，IntPtr lParam，布尔值和处理)MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o)在System.Windows.Threading.ExceptionWrapper.InternalRealCall(委托回调，对象args，Int32 numArgs)System.Windows.Threading.ExceptionWrapper.TryCatchWhen(对象源，委托回调，对象args，Int32 numArgs，委托catchHandler)在System.Windows.Threading.Dispatcher.LegacyInvokeImpl(DispatcherPriority优先级，TimeSpan超时，委托方法，对象参数，Int32numArgs)在MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd，Int32msg，IntPtr wParam，IntPtr lParam)MS.Win32.UnsafeNativeMethods.DispatchMessage(MSG& msg)位于System.Windows.Threading.Dispatcher.PushFrameImpl(DispatcherFrame帧)System.Windows.Threading.Dispatcher.PushFrame(DispatcherFrame框架)在System.Windows.Application.RunDispatcher(Object ignore)在System.Windows.Application.RunInternal(窗口窗口)位于System.Windows.Application.Run(窗口"窗口)位于System.Windows.Application.Run()中的AntiBonto.App.Main()D:\ Marci \Programozás\ AntiBonto \ AntiBonto \ obj \ Debug \ App.g.cs:第0行位于System.AppDomain._nExecuteAssembly(RuntimeAssembly程序集，字符串[]args)位于System.AppDomain.ExecuteAssembly(String assemblyFile，证据assemblySecurity，String [] args)在Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()在System.Threading.ThreadHelper.ThreadStart_Context(对象状态)位于System.Threading.ExecutionContext.RunInternal(ExecutionContextexecutionContext，ContextCallback回调，对象状态，布尔值reserveSyncCtx)位于System.Threading.ExecutionContext.Run(ExecutionContextexecutionContext，ContextCallback回调，对象状态，布尔值reserveSyncCtx)位于System.Threading.ExecutionContext.Run(ExecutionContextexecutionContext，ContextCallback回调，对象状态)位于System.Threading.ThreadHelper.ThreadStart()
at System.Windows.Data.ListCollectionView.RestoreLiveShaping() at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs) at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler) at System.Windows.Threading.DispatcherOperation.InvokeImpl() at System.Windows.Threading.DispatcherOperation.InvokeInSecurityContext(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 MS.Internal.CulturePreservingExecutionContext.Run(CulturePreservingExecutionContext 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, Int32 numArgs) at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler) at System.Windows.Threading.Dispatcher.LegacyInvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Int32 numArgs) 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.Application.RunDispatcher(Object ignore) at System.Windows.Application.RunInternal(Window window) at System.Windows.Application.Run(Window window) at System.Windows.Application.Run() at AntiBonto.App.Main() in D:\Marci\Programozás\AntiBonto\AntiBonto\obj\Debug\App.g.cs:line 0 at System.AppDomain._nExecuteAssembly(RuntimeAssembly 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.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()
推荐答案
我不知道为什么，但这已修复了该错误:
I have no idea why, but this fixed the bug:
public ICollectionView Team
{
get
{
CollectionViewSource cvs = new CollectionViewSource { Source = People, IsLiveFilteringRequested = true, LiveFilteringProperties = { "Num" } };
cvs.View.Filter = p => ((Person)p).Num != 11;
cvs.View.CollectionChanged += EmptyEventHandler;
return cvs.View;
}
}
private void EmptyEventHandler(object sender, NotifyCollectionChangedEventArgs e) { }
我正在尝试调试异常发生的位置，并且我想在集合更改时设置一个断点.订阅该事件使异常消失.
I was trying to debug where the exception happens, and I wanted to set a breakpoint when the collection changes. Subscribing to the event made the exception go away.
这篇关于PresentationFramework中的NullReference异常的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
