WPF：將ListBox ContextMenu的命令參數綁定到ListBox的選定項目

Question

是否可以將ListBox ContextMenu的CommandParameter綁定到ListBox的Selected Item？我應該說ContCommand是在主窗口中，當點擊上下文菜單項時調用 - 但是，我需要讓參數正常工作。

我試過，但綁定失敗：

<Window x:Class="ListBoxContextMenu.MainWindow" 
     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
     xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
     xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
     xmlns:local="clr-namespace:ListBoxContextMenu" 
     mc:Ignorable="d" 
     Title="MainWindow" Height="350" Width="525"> 

    <Grid> 
     <StackPanel> 
      <TextBlock Text="ListBox here:"/> 
      <ListBox ItemsSource="{Binding Items}" MinHeight="100" TabIndex="0" x:Name="LB"> 
       <ListBox.ContextMenu> 
        <ContextMenu> 
         <MenuItem Header="Foo" Command="{Binding ContCommand}" CommandParameter="{Binding RelativeSource={RelativeSource AncestorType={x:Type ListBox}},Path=SelectedItem}"/> 
        </ContextMenu> 
       </ListBox.ContextMenu> 
      </ListBox> 
     </StackPanel> 
    </Grid> 
</Window> 

C＃代碼主窗口：

using System.Collections.ObjectModel; 
using System.Windows; 
using System.Windows.Input; 
using MvvmFoundation.Wpf; 

    namespace ListBoxContextMenu 
    { 
     public partial class MainWindow : Window 
     { 
      public MainWindow() 
      { 
       InitializeComponent(); 
       DataContext = this; 
       Loaded += (sender, e) => MoveFocus(new TraversalRequest(FocusNavigationDirection.Next)); 
       ContCommand = new RelayCommand<object>((object o) => 
       { 
        System.Diagnostics.Debug.WriteLine("Context Menu pressed"); 
       }); 
      } 

      public ObservableCollection<string> Items { get; set; } = new ObservableCollection<string>{"Fred", "Jim", "Sheila"}; 
      public RelayCommand<object> ContCommand { get; set; } 
     } 
    } 

Answer 1

的ListBox不是ContextMenu的視覺祖先，因爲後者駐留在自己的視覺樹。

但是你可以綁定到ContextMenu的PlacementTarget，這是ListBox。

這工作：

<ListBox ItemsSource="{Binding Items}" MinHeight="100" TabIndex="0" x:Name="LB"> 
    <ListBox.ContextMenu> 
     <ContextMenu> 
      <MenuItem Header="Foo" Command="{Binding ContCommand}" 
           CommandParameter="{Binding RelativeSource={RelativeSource AncestorType={x:Type ContextMenu}}, 
           Path=PlacementTarget.SelectedItem}"/> 
     </ContextMenu> 
    </ListBox.ContextMenu> 
</ListBox> 

Answer 2

上下文菜單在不同的樹，所以結合是棘手視情況而定。這裏有兩個選項：

綁定到通過其名稱列表框如

Binding SelectedItem, ElementName=LB 

使用參考名稱

有時元素名稱綁定失敗和一個具有至使用x：ref名稱（你有）

Binding Source={x:Reference LB}, Path=SelectedItem 

---

至於爲什麼，引用x:Reference

In WPF and XAML 2006, element references are addressed by the framework-level feature of ElementName binding. For most WPF applications and scenarios, ElementName binding should still be used. Exceptions to this general guidance might include cases where there are data context or other scoping considerations that make data binding impractical and where markup compilation is not involved.

Answer 3

添加Mode=FindAncestor到RelativeSource結合。

CommandParameter="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type ListBox}}, Path=SelectedItem}"