当通过样式设置器设置上下文菜单时，PlacementTarget属性为空。

Question

当通过样式设置器设置上下文菜单时，PlacementTarget属性为空。

5

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，我有两个属性：第一个是项目列表，第二个是命令。我想在ListView中显示来自第一个属性的项目。此外，我希望为每个项目都有一个上下文菜单，单击它将激活第二个属性的命令。

以下是我的视图模型代码：

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"
            }));
        }
    }

现在是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：直到我实际打开上下文菜单，上下文菜单的PlacementTarget为null。在命令的“CanExecute”被调用之前，我需要以某种方式将所单击的ListViewItem的数据上下文接收到 - 我真的希望所有内容都在XAML中完成，而不需要处理任何代码后台回调。

提前感谢您。

- Illidan

1个回答

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- anivas · Accepted Answer

如果你正在寻找 ListViewItem 的 DataContext，你可以这样做： CommandParameter="{Binding}" 编辑 - 这是我尝试过的：

public partial class MainWindow : Window
{
    private ObservableCollection<Person> list = new ObservableCollection<Person>();

    public MainWindow()
    {
        InitializeComponent();
        list.Add(new Person() { Name = "Test 1"});
        list.Add(new Person() { Name = "Test 2"});
        list.Add(new Person() { Name = "Test £"});
        list.Add(new Person() { Name = "Test 4"});
        this.DataContext = this;

    }

    public static ICommand MyCommand //this is a command, I want to be able execute from context menu of each item     
    {         
        get
        {
            return new DelegateCommand<Person>(
                a => Console.WriteLine(a.Name),
                a => true);
        }
    }

    public ObservableCollection<Person> Items
    {
        get
        {
            return this.list;
        }
    }
}

public class Person
{
    public string Name { get; set; }
}

而且xaml：

<Window x:Class="ListView1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:ListView1="clr-namespace:ListView1" Title="MainWindow" Height="350" Width="525">
    <Grid>
        <ListView ItemsSource="{Binding Items}">            
            <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="{x:Static ListView1:MainWindow.MyCommand}"  CommandParameter="{Binding}" />
                            </ContextMenu>
                        </Setter.Value>
                    </Setter>
                </Style>
            </ListView.ItemContainerStyle>
        </ListView>
    </Grid>
</Window>