仅在选择 ListViewItem 时显示内容

Question

I have a ListBox when one of the ListBoxItems are selected I want to change the visibility of the button "View" and display it.这意味着默认状态是隐藏。

这可能吗？如果可以，我是否可以使用 XAML 中的触发器或代码隐藏来解决此问题？

XAML 片段

<ListBox Background="Transparent" 
      ItemContainerStyle="{StaticResource listBoxTemplate}" BorderThickness="0">
    <ListBox.ItemsPanel>
        <ItemsPanelTemplate>
            <StackPanel Orientation="Vertical" VerticalAlignment="Center" />
        </ItemsPanelTemplate>
    </ListBox.ItemsPanel>
    <ListBox.ItemTemplate>
        <DataTemplate>
            <Grid Background="Beige" Margin="10 10 10 10" 
                    HorizontalAlignment="Center" Width="500" Height="100"
                    VerticalAlignment="Stretch">
                <Grid.RowDefinitions>
                    <RowDefinition Name="TopRow" Height="50" />
                    <RowDefinition Name="BottomRow" Height="*" />
                </Grid.RowDefinitions>
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Name="LeftSideMenu" Width="*"/>
                    <ColumnDefinition Name="Middle" Width="*"/>
                </Grid.ColumnDefinitions>
                <Label Grid.Column="0" Grid.Row="0" Content="{Binding name}" />

                <Button Grid.Column="1" VerticalAlignment="Center" 
                    Grid.RowSpan="2" Name="view" Click="viewClicked_Click"
                    Grid.Row="0">View</Button>

                <Label Grid.Column="0" Grid.Row="1" 
                    Content="{Binding description}" />
            </Grid>
        </DataTemplate>
    </ListBox.ItemTemplate>
</ListBox>

Answer 1

[旧的无用代码]

---

编辑： 好吧，我没有很好地阅读这个问题，但这应该可以解决问题： 将DataTemplate 中的按钮替换为：

<Button Grid.Row="0" Grid.Column="1" Grid.RowSpan="2" VerticalAlignment="Center"
        Name="view" Click="viewClicked_Click"
        Content="View">
 <Button.Style>
  <Style TargetType="{x:Type Button}">
   <Setter Property="Visibility" Value="Collapsed"/>
   <Style.Triggers>
    <DataTrigger Binding="{Binding 
                           RelativeSource={RelativeSource Mode=FindAncestor,
                           AncestorType={x:Type ListBoxItem}},Path=IsSelected}" 
                 Value="True">
     <Setter Property="Visibility" Value="Visible"/>
    </DataTrigger>
   </Style.Triggers>
  </Style>
 </Button.Style>
</Button>

这里发生的是样式将 Visibility 属性设置为 Collapsed 并使用触发器来更改它。我使用了DataTrigger，所以你可以使用{Binding ...}。 使用{Binding RelativeSource={..}}，您可以查找祖先，这里我们正在寻找ListBoxItem 类型的祖先。

这样做是在 WPF 树中“向上”查找，以查看此按钮是否具有类型为 ListBoxItem 的 Parent 对象，如果找到，它将检查 IsSelected (Path=IsSelected) 属性是否为 True，并且将然后更新按钮的可见性属性。

我希望这个解释是有道理的！ :-)

---

编辑2： 只是为了好玩，背后的代码方式：

private Button _previousButton;
private void listBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
 if (_previousButton != null)
  _previousButton.Visibility = Visibility.Collapsed;

 // Make sure an item is selected
 if (listBox.SelectedItems.Count == 0)
  return;

 // Get the first SelectedItem (use a List<object> when 
 // the SelectionMode is set to Multiple)
 object selectedItem = listBox.SelectedItems[0];
 // Get the ListBoxItem from the ContainerGenerator
 ListBoxItem listBoxItem = listBox.ItemContainerGenerator.ContainerFromItem(selectedItem) as ListBoxItem;
 if (listBoxItem == null)
  return;

 // Find a button in the WPF Tree
 Button button = FindDescendant<Button>(listBoxItem);
 if (button == null)
  return;

 button.Visibility = Visibility.Visible;
 _previousButton = button;
}

/// <summary>
/// Finds the descendant of a dependency object.
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="obj">The obj.</param>
/// <returns></returns>
public static T FindDescendant<T>(DependencyObject obj) where T : DependencyObject
{
 // Check if this object is the specified type
 if (obj is T)
  return obj as T;

 // Check for children
 int childrenCount = VisualTreeHelper.GetChildrenCount(obj);
 if (childrenCount < 1)
  return null;

 // First check all the children
 for (int i = 0; i < childrenCount; i++)
 {
  DependencyObject child = VisualTreeHelper.GetChild(obj, i);
  if (child is T)
   return child as T;
 }

 // Then check the childrens children
 for (int i = 0; i < childrenCount; i++)
 {
  DependencyObject child = FindDescendant<T>(VisualTreeHelper.GetChild(obj, i));
  if (child != null && child is T)
   return child as T;
 }

 return null;
}

我建议你使用 XAML 触发器“方式”，因为它更干净...

Answer 2

对列表中的选定项目使用转换器来确定可见性。

<Button Visibility="{Binding ElementName=lb, Path=SelectedItem, Converter={StaticResource TestConverter}}" />

这里是值转换器

public class TestConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (value == null)
            return Visibility.Collapsed;
        else
            return Visibility.Visible;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new Exception("The method or operation is not implemented.");
    }
}

Answer 3

如果您使用 MVVM 模式，您应该将您的按钮绑定到 ICommand，例如来自 MVVM Toolkit 的 DelegateCommand。这样，按钮将使用命令的 CanExecute() 状态自行决定是否应启用。