Question

我正在尝试使用使用MVVM Light的CommandParameter来使用RelayCommand。该命令在我的viewmodel中定义，我想传递选定的ListBox项作为参数。该命令是绑定的，但参数不是。这可能吗？

<UserControl x:Class="Nuggets.Metro.Views.EmployeeListView"
         ...
         DataContext="{Binding EmployeeList,Source={StaticResource Locator}}">
   <ListBox x:Name="lstEmployee" ItemsSource="{Binding EmployeeItems}" Style="{StaticResource EmployeeList}" Tag="{Binding EmployeeItems}">
        <ListBox.ContextMenu>
            <ContextMenu DataContext="{Binding Path=PlacementTarget.Tag, RelativeSource={RelativeSource Self}}">
                <MenuItem Header="Edit item" Command="{Binding EditEmployeeCommand}" CommandParameter="{Binding PlacementTarget.SelectedItem,RelativeSource={RelativeSource AncestorType={x:Type ContextMenu}}}"/>
                <MenuItem Header="Delete item" Command="{Binding DeleteEmployeeCommand}" CommandParameter="{Binding PlacementTarget.SelectedItem,RelativeSource={RelativeSource AncestorType={x:Type ContextMenu}}}"/>
            </ContextMenu>
        </ListBox.ContextMenu>

Answer 1

~~这应该有效~~

<ContextMenu DataContext="{Binding Path=PlacementTarget.Tag, RelativeSource={RelativeSource Self}}"> <MenuItem Header="Edit item" Command="{Binding EditEmployeeCommand}" CommandParameter="{Binding SelectedItem,ElementName=lstEmployee}"/> <MenuItem Header="Delete item" Command="{Binding DeleteEmployeeCommand}" CommandParameter="{Binding SelectedItem,ElementName=lstEmployee}"/> </ContextMenu>

~~在CommandParameter的绑定中使用ListBox als ElementName的名称，并将路径设置为SelectedItem。~~

<强>更新

上面的代码不适用于ListBox和ContextMenu，因为它们属于不同的可视树。结果是

System.Windows.Data Error: 4 : Cannot find source for binding with reference 'ElementName=lstEmployee'. BindingExpression:Path=SelectedItem; DataItem=null; target element is 'MenuItem' (Name=''); target property is 'CommandParameter' (type 'Object')

以下XAML完成了这项工作。使用ContextMenu的PlacementTarget（即ListBox）。

<ContextMenu DataContext="{Binding Path=PlacementTarget.Tag, RelativeSource={RelativeSource Self}}">
  <MenuItem Header="Edit item" 
            Command="{Binding EditEmployeeCommand}" 
            CommandParameter="{Binding RelativeSource={RelativeSource AncestorType=ContextMenu}, Path=PlacementTarget.SelectedItem}"/>
  <MenuItem Header="Delete item" 
            Command="{Binding DeleteEmployeeCommand}"
            CommandParameter="{Binding RelativeSource={RelativeSource AncestorType=ContextMenu}, Path=PlacementTarget.SelectedItem}"/>
</ContextMenu>

Answer 2

这适用于带有MVVM的TreeView或ListView。 ContextMenu中的PlacementTarget是（这里）Listview

<ListView.ContextMenu>
  <ContextMenu>
     <MenuItem x:Name="OpenExplorer"Header="ShowFolder"                  
      Command="{Binding ShowExplorer}"
      CommandParameter ="{Binding Path=PlacementTarget.SelectedItem,
            RelativeSource={RelativeSource AncestorType=ContextMenu}}"/>
   </ContextMenu>
</ListView.ContextMenu>

带MVVM Light的CommandParameter

2 个答案: