用列表显示上下文菜单项的可见性

Question

我在ListBox上附加了一个ContextMenu，它提供了两个选项：创建和删除元素。如果ListBox数据为空，我只想隐藏"Delete"元素。

我曾尝试将属性"Visibility"与视图代码中的一个变量绑定，将其设置为"Collapsed"或"Visible"，但没有成功。

XAML:

<ListBox ItemsSource="{Binding ElementList}"
SelectedItem="{Binding SelectedElement}"
SelectionChanged="ListBoxProjects_SelectionChanged">
<ListBox.ItemTemplate>
<DataTemplate>
<Grid>
<TextBlock Text="{Binding Name}" />
</Grid>
</DataTemplate>
</ListBox.ItemTemplate>
<ListBox.ContextMenu>
<ContextMenu>
<MenuItem Name="Add" Click="Add_Click" Header="Add element" />
<MenuItem Name="Delete" Click="Delete_Click" 
HeaderStringFormat="Delete element {0}" 
Header="{Binding SelectedElement.Name}" 
Visibility="{Binding ElementContextMenuVisibility}" />
</ContextMenu>
</ListBox.ContextMenu>
</ListBox>

CS:

public partial class View : UserControl
{
private ViewModel _viewModel = ViewModel.Instance;
private Visibility _elementContextMenuVisibility { get; set; }
public Visibility ElementContextMenuVisibility
{
get { return _elementContextMenuVisibility; }
set { _elementContextMenuVisibility = value; }
}
public View()
{
InitializeComponent();
}
private void ListBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
if (_viewModel.ElementList != null && _viewModel.ElementList.Count > 0)
ElementContextMenuVisibility = Visibility.Visible;
else
ElementContextMenuVisibility = Visibility.Collapsed;
}
}

感谢

Answer 1

您可以通过RelativeSource绑定实现这一点，而不需要xaml.cs代码。

XAML

<ListBox ItemsSource="{Binding ElementList}"
SelectedItem="{Binding SelectedElement}">
<ListBox.Resources>
<BooleanToVisibilityConverter x:Key="BooleanToVisibilityConverter"/>
</ListBox.Resources>
<ListBox.ItemTemplate>
<DataTemplate>
<Grid>
<TextBlock Text="{Binding Name}" />
</Grid>
</DataTemplate>
</ListBox.ItemTemplate>
<ListBox.ContextMenu>
<ContextMenu>
<MenuItem Name="Add" Click="Add_Click" Header="Add element" />
<MenuItem Name="Delete" Click="Delete_Click" 
HeaderStringFormat="Delete element {0}" 
Header="{Binding SelectedElement.Name}" 
Visibility="{Binding PlacementTarget.HasItems, RelativeSource={RelativeSource AncestorType=ContextMenu}, Converter={StaticResource BooleanToVisibilityConverter}}" />
</ContextMenu>
</ListBox.ContextMenu>
</ListBox>