我在尝试提交空 DataGrid 行时遇到异常。
System.NullReferenceException: Object reference not set to an instance of an object.
at MS.Internal.Data.PropertyPathWorker.DetermineWhetherDBNullIsValid()
at MS.Internal.Data.PropertyPathWorker.get_IsDBNullValidForUpdate()
at MS.Internal.Data.ClrBindingWorker.get_IsDBNullValidForUpdate()
at System.Windows.Data.BindingExpression.ConvertProposedValue(Object value)
at System.Windows.Data.BindingExpressionBase.UpdateValue()
at System.Windows.Data.BindingExpression.Update(Boolean synchronous)
at System.Windows.Data.BindingExpression.UpdateSource()
at Microsoft.Windows.Controls.DataGridHelper.UpdateSource(FrameworkElement element, DependencyProperty dp)
at Microsoft.Windows.Controls.DataGridTextColumn.CommitCellEdit(FrameworkElement editingElement)
at Microsoft.Windows.Controls.DataGridColumn.CommitEdit(FrameworkElement editingElement)
at Microsoft.Windows.Controls.DataGridCell.CommitEdit()
at Microsoft.Windows.Controls.DataGrid.OnExecutedCommitEdit(ExecutedRoutedEventArgs e)
at Microsoft.Windows.Controls.DataGrid.OnExecutedCommitEdit(Object sender, ExecutedRoutedEventArgs e)
at System.Windows.Input.CommandBinding.OnExecuted(Object sender, ExecutedRoutedEventArgs e)
at System.Windows.Input.CommandManager.ExecuteCommandBinding(Object sender, ExecutedRoutedEventArgs e, CommandBinding commandBinding)
at System.Windows.Input.CommandManager.FindCommandBinding(CommandBindingCollection commandBindings, Object sender, RoutedEventArgs e, ICommand command, Boolean execute)
at System.Windows.Input.CommandManager.FindCommandBinding(Object sender, RoutedEventArgs e, ICommand command, Boolean execute)
at System.Windows.Input.CommandManager.OnExecuted(Object sender, ExecutedRoutedEventArgs e)
at System.Windows.UIElement.OnExecutedThunk(Object sender, ExecutedRoutedEventArgs e)
at System.Windows.Input.ExecutedRoutedEventArgs.InvokeEventHandler(Delegate genericHandler, Object target)
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.RoutedCommand.ExecuteImpl(Object parameter, IInputElement target, Boolean userInitiated)
at System.Windows.Input.RoutedCommand.Execute(Object parameter, IInputElement target)
at Microsoft.Windows.Controls.DataGrid.EndEdit(RoutedCommand command, DataGridCell cellContainer, DataGridEditingUnit editingUnit, Boolean exitEditMode)
at Microsoft.Windows.Controls.DataGrid.CommitEdit(DataGridEditingUnit editingUnit, Boolean exitEditingMode)
at Microsoft.Windows.Controls.DataGrid.CommitAnyEdit()
at Microsoft.Windows.Controls.DataGrid.OnEnterKeyDown(KeyEventArgs e)
at Microsoft.Windows.Controls.DataGrid.OnKeyDown(KeyEventArgs e)
at System.Windows.UIElement.OnKeyDownThunk(Object sender, KeyEventArgs e)
at System.Windows.Input.KeyEventArgs.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 System.Windows.Input.InputProviderSite.ReportInput(InputReport inputReport)
at System.Windows.Interop.HwndKeyboardInputProvider.ReportInput(IntPtr hwnd, InputMode mode, Int32 timestamp, RawKeyboardActions actions, Int32 scanCode, Boolean isExtendedKey, Boolean isSystemKey, Int32 virtualKey)
at System.Windows.Interop.HwndKeyboardInputProvider.ProcessKeyAction(MSG& msg, Boolean& handled)
at System.Windows.Interop.HwndSource.CriticalTranslateAccelerator(MSG& msg, ModifierKeys modifiers)
at System.Windows.Interop.HwndSource.OnPreprocessMessage(Object param)
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)
Exception calling "Run" with "1" argument(s): "Object reference not set to an instance of an object."
重现步骤:
这工作正常:
也:
来源可以找到here .
我发现了两个似乎与此问题有关的帖子:
另外,我在 C# 中尝试了类似的代码,并且效果很好。
我该如何解决这个问题?
最佳答案
这似乎是 Microsoft WPF DataGrid 中的一个错误。您一定要通过 Microsoft Connect 举报,如果你还没有这样做。
作为一种解决方法,您可以在绑定(bind)上使用值转换器,以阻止绑定(bind)目标上的 NULL 值传输到绑定(bind)源,这将导致 空引用异常 .以下是此类转换器的示例:
// NullToUnsetConverter.cs
using System;
using System.Windows;
using System.Windows.Data;
using System.Globalization;
namespace MyProject.Controls.Converters
{
/// <summary>
/// Converts <c>null</c> values to <see cref="DependencyProperty.UnsetValue"/>.
/// <remarks>
/// This converter is intented for use in situations when the binding target
/// does not correctly handle <c>null</c> values. This is the case for example
/// with some WPF UI controls.
/// </remarks>
/// </summary>
public class NullToUnsetConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value == null)
{
return DependencyProperty.UnsetValue;
}
else
{
// No conversion applied
return value;
}
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
// No conversion applied
return value;
}
}
}
为了将转换器应用于您的绑定(bind),您必须像这样修改您的 XAML:
<Window
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:cnv="clr-namespace:MyProject.Controls.Converters"
xmlns:sys="clr-namespace:System;assembly=mscorlib"
xmlns:dg="clr-namespace:Microsoft.Windows.Controls;assembly=WpfToolkit"
>
<Window.Resources>
<x:Array x:Key="people" Type="sys:Object" />
<cnv:NullToUnsetConverter x:Key="NullToUnsetConverter" />
</Window.Resources>
<StackPanel>
<dg:DataGrid ItemsSource="{DynamicResource people}" CanUserAddRows="True" AutoGenerateColumns="False">
<dg:DataGrid.Columns>
<dg:DataGridTextColumn Header="First" Binding="{Binding First, Converter={StaticResource NullToUnsetConverter}}" />
<dg:DataGridTextColumn Header="Last" Binding="{Binding Last, Converter={StaticResource NullToUnsetConverter}}" />
</dg:DataGrid.Columns>
</dg:DataGrid>
</StackPanel>
</Window>
或者,您可以修改 NullToUnsetConverter.Convert 返回 的方法空字符串 当输入值是一个字符串时,就像你的情况一样。
关于wpf - PowerShell WPF 数据网格 : Exception thrown committing empty row,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/689852/