c# - ListBoxItem ContextMenu 仅当 ListBox 选择多个项目时

Question

当未选择任何项目或仅选择一个项目时，如何禁用列表框项目上下文菜单？

ListBox 有一个 SelectedItems 属性，但它是只读的，您不能绑定(bind)到它。

<ListBox ItemsSource="{Binding Items}" SelectionMode="Extended">
    <ListBox.ItemContainerStyle>
        <Style TargetType="ListBoxItem">
            <Setter Property="ContextMenu">
                <Setter.Value>
                    <ContextMenu>
                        <MenuItem Header="GOGO" />
                    </ContextMenu>
                </Setter.Value>
            </Setter>
        </Style>
    </ListBox.ItemContainerStyle>
    <ListBox.ItemTemplate>
        <DataTemplate>
                <TextBlock Text="{Binding}" HorizontalAlignment="Center" VerticalAlignment="Center" />
        </DataTemplate>
    </ListBox.ItemTemplate>
</ListBox>

Answer 1

这应该有效:

<ListBox ItemsSource="{Binding Items}" SelectionMode="Extended">
    <ListBox.ItemContainerStyle>
        <Style TargetType="ListBoxItem">
            <Setter Property="ContextMenu">
                <Setter.Value>
                    <ContextMenu>
                        <MenuItem Header="GOGO" />
                    </ContextMenu>
                </Setter.Value>
            </Setter>
            <Style.Triggers>
                <DataTrigger Binding="{Binding SelectedItems.Count, RelativeSource={RelativeSource AncestorType={x:Type ListBox}}}" Value="0">
                    <Setter Property="ContextMenu" Value="{x:Null}" />
                </DataTrigger>
                <DataTrigger Binding="{Binding SelectedItems.Count, RelativeSource={RelativeSource AncestorType={x:Type ListBox}}}" Value="1">
                    <Setter Property="ContextMenu" Value="{x:Null}" />
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </ListBox.ItemContainerStyle>
    <ListBox.ItemTemplate>
        <DataTemplate>
            <TextBlock Text="{Binding}" HorizontalAlignment="Center" VerticalAlignment="Center" />
        </DataTemplate>
    </ListBox.ItemTemplate>
</ListBox>

添加两个 DataTrigger 检查 SelectedItems.Count 是 0 还是 1，在这种情况下，它将 ContextMenu 设置为 { x:Null.