c# - ArgumentException 与 ListView SelectedItem 的属性和 TextBox 绑定(bind)

Question

编辑:

我发现这个问题的根源是 Bar 中的 Equals() 和 GetHashCode() 实现。

特别是参与 GetHashCode() 并且还绑定(bind)到 TextBox< 的属性(如 Bar 中的 Name)/。删除这些覆盖方法后一切正常(除了我想保留它们)

我不明白为什么会这样？

---

我有一个 TextBox、一个 ListView 和一些与以下 ViewModel 的数据绑定(bind):

[PropertyChanged.ImplementPropertyChanged]
public class ViewModel
{
    public ObservableCollection<Foo> Foos { get; set; }

    public Foo SelectedFoo { get; set; }
}

[PropertyChanged.ImplementPropertyChanged]
public class Foo
{
    public Bar FooBar { get; set; }
}

[PropertyChanged.ImplementPropertyChanged]
public class Bar
{
    public string Name { get; set; }

    public override bool Equals(object obj)
    {
        var other = obj as Bar;

        if (other != null)
        {
            return other.Name == Name;
        }

        return false;
    }

    public override int GetHashCode()
    {
        return Name.GetHashCode();
    }
}

这是我的 list :

<ListView x:Name="V_List" SelectedItem="{Binding SelectedFoo}"  ItemsSource="{Binding Path=Foos}" SelectionMode="Single">
    ...
</ListView>

这是我的文本框:

<TextBox Text="{Binding Path=SelectedFoo.FooBar.Name, Mode=TwoWay, UpdateSourceTrigger=LostFocus}" />

事情是这样的:

当我从 List 中选择第一个 Foo 时，绑定(bind)起作用，并且 FooBar 的 Name所选 Foo 的属性出现在 TextBox 中。无论我更改选择多少次，适当的值都会出现在 TextBox 中。

但是现在，如果我使用 TextBox 更改 Name(在失去焦点后，由于 TwoWay 数据绑定(bind)，它正在工作，我检查了 Debugging)然后更改列表中的选择，TextBox 仍显示先前选择的项目的值。

此外，再次选择相同的项目，然后选择其他一些项目，我得到以下异常(令人惊讶的是，调试器没有报告，我不得不将它记录到一个文件中。可能是因为异常是不是从我的代码中引发的。)

这是日志:

The Exception is:-Exception :: System.ArgumentException: An item with the same key has already been added. at System.ThrowHelper.ThrowArgumentException(ExceptionResource resource) at System.Collections.Generic.Dictionary2.Insert(TKey key, TValue
value, Boolean add) at
System.Collections.Generic.Dictionary2..ctor(IDictionary2
dictionary, IEqualityComparer1 comparer) at System.Windows.Controls.Primitives.Selector.InternalSelectedItemsStorage..ctor(InternalSelectedItemsStorage collection, IEqualityComparer`1 equalityComparer) at System.Windows.Controls.Primitives.Selector.SelectionChanger.ApplyCanSelectMultiple() at System.Windows.Controls.Primitives.Selector.SelectionChanger.End() at System.Windows.Controls.Primitives.Selector.SetSelectedHelper(Object item, FrameworkElement UI, Boolean selected) at System.Windows.Controls.Primitives.Selector.NotifyIsSelectedChanged(FrameworkElement container, Boolean selected, RoutedEventArgs e) at System.Windows.Controls.Primitives.Selector.OnSelected(Object sender, RoutedEventArgs e) 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 e) at System.Windows.Controls.ListBoxItem.OnSelected(RoutedEventArgs e)
at System.Windows.Controls.ListBoxItem.OnIsSelectedChanged(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.SetCurrentValueInternal(DependencyProperty dp, Object value) at System.Windows.Controls.ListBox.NotifyListItemClicked(ListBoxItem item, MouseButton mouseButton) at System.Windows.Controls.ListBoxItem.HandleMouseButtonDown(MouseButton mouseButton) at System.Windows.Controls.ListBoxItem.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 System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)

我注意到的另一件值得一提的事情是，如果我将 ListView 的 SelectionMode 设置为 Multiple，则不会引发异常。在这种情况下，List 中我从 TextBox 中更改了其 FooBar 值的项目以及我更改的任何其他项目仍然处于选中状态之后可以选择then。

注意:我正在使用 Fody/PropertyChanged实现 INotifyCollectionChanged。

Answer 1

What I don't understand is WHY is this happening?

我不能给你一个明确的答案，但从错误来看，ListView 似乎保留了控件项的内部字典。此外，我敢打赌该内部字典的键是基于 GetHashCode 的值。问题是当对象仍然是控件的一部分时，您允许用户更改该键(通过更改名称属性)。我猜想在选择更改时它通过根据需要添加和删除项目来维护字典。由于您项目的有效“键”已更改，它可能会尝试将其读入内部字典，却发现该项目已经在字典中(但在原始键下)。

您可以通过在名称更改时删除更改的项目并将其读取到 Foos 集合来测试该理论。这应该使用正确的新 key 清除并重新插入内部字典中的项目。