通过样式设置器设置contextmenu时，PlacementTarget属性为null

Question

在我的应用程序中，我有一个视图（ListView）和一个视图模型。在视图模型内部，我有2个属性：第一个是项目列表，第二个是命令。我想在ListView中显示项目（从第一个属性开始）。另外，我希望每个菜单都有一个上下文菜单，单击该菜单将激活一个命令（来自第二个属性）。

这是我的视图模型的代码：

public class ViewModel
{
    public IEnumerable Items
    {
        get
        {
            return ...;  //returns a collection of items
        }
    }

    public ICommand MyCommand //this is a command, I want to be able execute from context menu of each item
    {
        get
        {
            return new DelegateCommand(new Action<object>(delegate(object parameter)
            {
                //here code of the execution   
            }
            ), new Predicate<object>(delegate(object parameter)
            {
                //here code of "can execute"
            }));
        }
    }

现在，XAML部分：

<ListView  ItemsSource="{Binding Items}">
<ListView.Resources>
    <commanding:CommandReference x:Key="myCommand" Command="{Binding MyCommand}"/>
</ListView.Resources>
    <ListView.ItemTemplate>
        <DataTemplate>
            <TextBlock 
                    Text="{Binding Name}"
                    />
        </DataTemplate>
    </ListView.ItemTemplate>
    <ListView.ItemContainerStyle>
        <Style TargetType="{x:Type ListViewItem}">
            <Setter Property="ContextMenu">
                <Setter.Value>
                    <ContextMenu>
                        <MenuItem 
                            Header="Remove from workspace" 
                            Command="{StaticResource myCommand}"
                            CommandParameter="HERE I WANT TO PASS THE DATA CONTEXT OF THE ListViewItem"
                            />
                    </ContextMenu>
                </Setter.Value>
            </Setter>
        </Style>
    </ListView.ItemContainerStyle>
</ListView>

问题：在我真正打开上下文菜单之前，上下文菜单的PlacementTarget为null。我需要某种方式来将单击的ListViewItem的数据上下文接收到命令的“ CanExecute”中，然后再调用该命令-我确实希望在XAML中进行所有操作，而无需处理后面的代码中的任何回调。

先感谢您。

Answer 1

如果您正在寻找 ListViewItem\'s，DataContext您可以这样做：

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CommandParameter="{Binding}"

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编辑-这是我尝试过的：

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public partial class MainWindow : Window\n{\n    private ObservableCollection<Person> list = new ObservableCollection<Person>();\n\n    public MainWindow()\n    {\n        InitializeComponent();\n        list.Add(new Person() { Name = "Test 1"});\n        list.Add(new Person() { Name = "Test 2"});\n        list.Add(new Person() { Name = "Test \xc2\xa3"});\n        list.Add(new Person() { Name = "Test 4"});\n        this.DataContext = this;\n\n    }\n\n    public static ICommand MyCommand //this is a command, I want to be able execute from context menu of each item     \n    {         \n        get\n        {\n            return new DelegateCommand<Person>(\n                a => Console.WriteLine(a.Name),\n                a => true);\n        }\n    }\n\n    public ObservableCollection<Person> Items\n    {\n        get\n        {\n            return this.list;\n        }\n    }\n}\n\npublic class Person\n{\n    public string Name { get; set; }\n}\n

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和 xaml：

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<Window x:Class="ListView1.MainWindow"\n        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"\n        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:ListView1="clr-namespace:ListView1" Title="MainWindow" Height="350" Width="525">\n    <Grid>\n        <ListView ItemsSource="{Binding Items}">            \n            <ListView.ItemTemplate>\n                <DataTemplate>\n                    <TextBlock Text="{Binding Name}" />\n                </DataTemplate>\n            </ListView.ItemTemplate>\n            <ListView.ItemContainerStyle>\n                <Style TargetType="{x:Type ListViewItem}">\n                    <Setter Property="ContextMenu">\n                        <Setter.Value>\n                            <ContextMenu>\n                                <MenuItem Header="Remove from workspace" Command="{x:Static ListView1:MainWindow.MyCommand}"  CommandParameter="{Binding}" />\n                            </ContextMenu>\n                        </Setter.Value>\n                    </Setter>\n                </Style>\n            </ListView.ItemContainerStyle>\n        </ListView>\n    </Grid>\n</Window>\n

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