WPF - 为什么ContextMenu项目适用于ListBox而不适用于ItemsControl？

Question

列表中的项目具有上下文菜单.上下文菜单项绑定到路由命令.

如果列表控件是a ListBox,则上下文菜单项可正常工作,但是一旦我将其降级为ItemsControl不再有效,它就会正常工作.具体来说,菜单项始终是灰色的.CanExecute我的回调CommandBinding也没有被调用.

它是什么ListBox允许上下文菜单项与命令正确绑定？

以下是一些示例应用程序的摘录,我将它们放在一起以突出显示问题:

<!-- Data template for items -->
<DataTemplate DataType="{x:Type local:Widget}">
  <StackPanel Orientation="Horizontal">
    <StackPanel.ContextMenu>
      <ContextMenu>
        <MenuItem Header="UseWidget" 
                  Command="{x:Static l:WidgetListControl.UseWidgetCommand}"
                  CommandParameter="{Binding}" />
      </ContextMenu>
    </StackPanel.ContextMenu>
    <TextBlock Text="{Binding Path=Name}" />
    <TextBlock Text="{Binding Path=Price}" />
  </StackPanel>
</DataTemplate>

<!-- Binding -->
<UserControl.CommandBindings>
  <CommandBinding Command="{x:Static l:WidgetListControl.UseWidgetCommand}" 
                  Executed="OnUseWidgetExecuted" 
                  CanExecute="CanUseWidgetExecute" />
</UserControl.CommandBindings>

<!-- ItemsControl doesn't work... -->
<ItemsControl ItemsSource="{Binding Path=Widgets}" />

<!-- But change it to ListBox, and it works! -->
<ListBox ItemsSource="{Binding Path=Widgets}" />

这是视图模型和数据项的C#代码:

public sealed class WidgetListViewModel
{
    public ObservableCollection<Widget> Widgets { get; private set; }

    public WidgetViewModel()
    {
        Widgets = new ObservableCollection<Widget>
            {
                new Widget { Name = "Flopple", Price = 1.234 },
                new Widget { Name = "Fudge", Price = 4.321 }
            };
    }
}

public sealed class Widget
{
    public string Name { get; set; }
    public double Price { get; set; }
}

这是控件的C#代码隐藏:

public partial class WidgetListControl
{
    public static readonly ICommand UseWidgetCommand 
        = new RoutedCommand("UseWidget", typeof(WidgetListWindow));

    public WidgetListControl()
    {
        InitializeComponent();
    }

    private void OnUseWidgetExecuted(object s, ExecutedRoutedEventArgs e)
    {
        var widget = (Widget)e.Parameter;
        MessageBox.Show("Widget used: " + widget.Name);
    }

    private void CanUseWidgetExecute(object s, CanExecuteRoutedEventArgs e)
    {
        e.CanExecute = true;
        e.Handled = true;
    }
}

只是重申一个问题 - 它是什么ListBox提供了允许它的上下文菜单项命令正确绑定,并且有什么方法可以使这个工作ItemsControl吗？

Answer 1

好吧,我看到的主要问题是ItemsControl没有所选项的概念,因此您无法选择要绑定到的DataTemplate项.

我不记得我在哪里看到它,但是在编写WPF时要遵循的一个好规则是使用控件来为您提供所需的行为,然后将其设置为您想要的样式.

因此,考虑到这一点,您需要ListBox的行为,但看看ItemsControl的外观,那么为什么不设置ListBoxItems的样式以不显示selected和non-selected之间的区别.

<Style TargetType="{x:Type ListBoxItem}">
    <Setter Property="Background" Value="Transparent"/>
    <Setter Property="HorizontalContentAlignment" Value="{Binding Path=HorizontalContentAlignment, RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}}"/>
    <Setter Property="VerticalContentAlignment" Value="{Binding Path=VerticalContentAlignment, RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}}"/>
    <Setter Property="Padding" Value="2,0,0,0"/>
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type ListBoxItem}">
                <Border SnapsToDevicePixels="true" x:Name="Bd" Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Padding="{TemplateBinding Padding}">
                    <ContentPresenter SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" VerticalAlignment="{TemplateBinding VerticalContentAlignment}"/>
                </Border>
                <ControlTemplate.Triggers>
                    <Trigger Property="IsEnabled" Value="false">
                        <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>
                    </Trigger>
                </ControlTemplate.Triggers>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>