我正在研究WPF并使用Devexpress工具进行GUI，
每当我调试我的程序时，它总是生成Null对象引用的异常并指向W1.SHOW();我创建了一个window2。
有人可以解释原因吗？
程序工作正常，但是当我点击按钮然后出现window2时，在那个窗口中我显示了两个标签。
Window2也会显示这两个标签，但是当我点击其中一个标签时，它会生成一个例外。我不知道为什么这样做：（
// using statements omitted for brevity...
namespace WpfApplication1
{
/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
CreateNavBarControl();
}
// When user will click NewDocumentButton, following function will get execute.
private void NewDocumentButton_Click(object sender, RoutedEventArgs e)
{
Window2 W1 = null;
//obj.ShowDialog();
//obj.Close();
if (W1 == null)
{
***W1 = new Window2();
W1.Show();***
}
}
}
}
Window2 - 代码
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Shapes;
namespace WpfApplication1
{
/// <summary>
/// Interaction logic for Window2.xaml
/// </summary>
public partial class Window2 : Window
{
public Window2()
{
InitializeComponent();
}
private void Window_Loaded(object sender, RoutedEventArgs e)
{
}
}
}
Window1 - XAML
<Window x:Class="WpfApplication1.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="News Room Computer System" Height="196" Width="331" xmlns:dx="http://schemas.devexpress.com/winfx/2008/xaml/core"
xmlns:dxn="http://schemas.devexpress.com/winfx/2008/xaml/navbar"
xmlns:dxb="http://schemas.devexpress.com/winfx/2008/xaml/bars"
dx:ThemeManager.ThemeName="MetropolisDark"
xmlns:dxe="http://schemas.devexpress.com/winfx/2008/xaml/editors"
Loaded="Window_Loaded" DataContext="{Binding}" xmlns:dxlc="http://schemas.devexpress.com/winfx/2008/xaml/layoutcontrol" Background="Black">
<Grid>
<DockPanel x:Name="dockPanel" Margin="5,25,0,0" Width="86" LastChildFill="False" HorizontalAlignment="Left">
</DockPanel>
<dxlc:LayoutGroup Margin="5,0,12,138" Name="layoutGroup1">
<Button Name="NewDocumentButton" Height="19" Width="45"
VerticalAlignment="Top" Content="New" Click="NewDocumentButton_Click" />
</dxlc:LayoutGroup>
</Grid>
</Window>
窗口2 - XAML
<Window x:Class="WpfApplication1.Window2"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Window2" Height="300" Width="300" xmlns:dxlc="http://schemas.devexpress.com/winfx/2008/xaml/layoutcontrol" Loaded="Window_Loaded" xmlns:dxe="http://schemas.devexpress.com/winfx/2008/xaml/editors">
<Grid>
<dxlc:LayoutGroup Header="LayoutGroup" Name="layoutGroup2" View="Tabs" Width="202" Height="175" Margin="38,20,38,66" ContextMenuClosing="layoutGroup2_ContextMenuClosing" ContextMenuOpening="layoutGroup2_ContextMenuClosing" DragEnter="layoutGroup2_DragEnter" MeasureSelectedTabChildOnly="True" SelectedTabIndex="2" DragScrolling="True">
<dxlc:LayoutGroup Header="ass" Name="layoutGroup3" Height="116" Width="153" />
<dxlc:LayoutControl Height="117" HorizontalAlignment="Left" dxlc:LayoutControl.TabHeader="va" Name="layoutControl1" VerticalAlignment="Top" Width="164">
<dxlc:LayoutItem Label="layoutItem1" Name="layoutItem1">
<dxe:TextEdit Name="textEdit1" />
</dxlc:LayoutItem>
</dxlc:LayoutControl>
</dxlc:LayoutGroup>
</Grid>
</Window>
// ---- STACKTRACE ------------------
System.NullReferenceException was unhandled
Message=Object reference not set to an instance of an object.
Source=DevExpress.Xpf.LayoutControl.v12.2
StackTrace:
at DevExpress.Xpf.LayoutControl.LayoutGroup.OnTabControlSelectionChanged()
at DevExpress.Xpf.LayoutControl.LayoutGroup.OnTabControlSelectionChanged(Object sender, TabControlSelectionChangedEventArgs e)
at DevExpress.Xpf.Core.DXTabControl.RaiseSelectionChanged(Int32 oldSelectedIndex)
at DevExpress.Xpf.Core.DXTabControl.OnSelectedIndexPropertyChanged(Int32 oldValue)
at DevExpress.Xpf.Core.DXTabControl.<.cctor>b__0(DependencyObject d, DependencyPropertyChangedEventArgs e)
at System.Windows.DependencyObject.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
at System.Windows.FrameworkElement.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
at System.Windows.DependencyObject.NotifyPropertyChange(DependencyPropertyChangedEventArgs args)
at System.Windows.DependencyObject.UpdateEffectiveValue(EntryIndex entryIndex, DependencyProperty dp, PropertyMetadata metadata, EffectiveValueEntry oldEntry, EffectiveValueEntry& newEntry, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType)
at System.Windows.DependencyObject.SetValueCommon(DependencyProperty dp, Object value, PropertyMetadata metadata, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType, Boolean isInternal)
at System.Windows.DependencyObject.SetValue(DependencyProperty dp, Object value)
at DevExpress.Xpf.Core.DXTabControl.OnSelectedItemPropertyChanged(Object oldValue)
at DevExpress.Xpf.Core.DXTabControl.<.cctor>b__1(DependencyObject d, DependencyPropertyChangedEventArgs e)
at System.Windows.DependencyObject.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
at System.Windows.FrameworkElement.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
at System.Windows.DependencyObject.NotifyPropertyChange(DependencyPropertyChangedEventArgs args)
at System.Windows.DependencyObject.UpdateEffectiveValue(EntryIndex entryIndex, DependencyProperty dp, PropertyMetadata metadata, EffectiveValueEntry oldEntry, EffectiveValueEntry& newEntry, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType)
at System.Windows.DependencyObject.SetValueCommon(DependencyProperty dp, Object value, PropertyMetadata metadata, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType, Boolean isInternal)
at System.Windows.DependencyObject.SetValue(DependencyProperty dp, Object value)
at DevExpress.Xpf.Core.DXTabControl.OnSelectedTabItemPropertyChanged(DXTabItem oldValue)
at DevExpress.Xpf.Core.DXTabControl.<.cctor>b__2(DependencyObject d, DependencyPropertyChangedEventArgs e)
at System.Windows.DependencyObject.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
at System.Windows.FrameworkElement.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
at System.Windows.DependencyObject.NotifyPropertyChange(DependencyPropertyChangedEventArgs args)
at System.Windows.DependencyObject.UpdateEffectiveValue(EntryIndex entryIndex, DependencyProperty dp, PropertyMetadata metadata, EffectiveValueEntry oldEntry, EffectiveValueEntry& newEntry, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType)
at System.Windows.DependencyObject.SetValueCommon(DependencyProperty dp, Object value, PropertyMetadata metadata, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType, Boolean isInternal)
at System.Windows.DependencyObject.SetValue(DependencyProperty dp, Object value)
at DevExpress.Xpf.Core.DXTabControl.DevExpress.Xpf.Core.ITabControl.SelectItem(DXTabItem item)
at DevExpress.Xpf.Core.DXTabItem.OnIsSelectedPropertyChanged()
at DevExpress.Xpf.Core.DXTabItem.<.cctor>b__2(DependencyObject d, DependencyPropertyChangedEventArgs e)
at System.Windows.DependencyObject.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
at System.Windows.FrameworkElement.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
at System.Windows.DependencyObject.NotifyPropertyChange(DependencyPropertyChangedEventArgs args)
at System.Windows.DependencyObject.UpdateEffectiveValue(EntryIndex entryIndex, DependencyProperty dp, PropertyMetadata metadata, EffectiveValueEntry oldEntry, EffectiveValueEntry& newEntry, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType)
at System.Windows.DependencyObject.SetValueCommon(DependencyProperty dp, Object value, PropertyMetadata metadata, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType, Boolean isInternal)
at System.Windows.DependencyObject.SetValue(DependencyProperty dp, Object value)
at DevExpress.Xpf.Core.DXTabItem.OnMouseLeftButtonClick(MouseButtonEventArgs e)
at DevExpress.Xpf.Core.DXTabItem.OnMouseLeftButtonDown(MouseButtonEventArgs e)
at System.Windows.UIElement.OnMouseLeftButtonDownThunk(Object sender, MouseButtonEventArgs e)
at System.Windows.Input.MouseButtonEventArgs.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.ReRaiseEventAs(DependencyObject sender, RoutedEventArgs args, RoutedEvent newEvent)
at System.Windows.UIElement.OnMouseDownThunk(Object sender, MouseButtonEventArgs e)
at System.Windows.Input.MouseButtonEventArgs.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.RaiseTrustedEvent(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 System.Windows.Input.InputProviderSite.ReportInput(InputReport inputReport)
at System.Windows.Interop.HwndMouseInputProvider.ReportInput(IntPtr hwnd, InputMode mode, Int32 timestamp, RawMouseActions actions, Int32 x, Int32 y, Int32 wheel)
at System.Windows.Interop.HwndMouseInputProvider.FilterMessage(IntPtr hwnd, WindowMessage msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
at System.Windows.Interop.HwndSource.InputFilterMessage(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 MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler)
at System.Windows.Threading.Dispatcher.InvokeImpl(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.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 WpfApplication1.App.Main() in C:\Documents and Settings\Administrator\My Documents\Visual Studio 2010\Projects\WpfApplication1\WpfApplication1\obj\x86\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.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx)
Detail: at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Threading.ThreadHelper.ThreadStart() InnerException:
答案 0 :(得分：1)
从SelectedTabIndex="2"中的LayoutGroup移除Window2声明。 LayoutGroup中没有足够的选项卡可供选择，这会导致NullReferenceException。
也许这是来自DevExpress的LayoutGroup的错误。
答案 1 :(得分：0)