ListBox.ContextMenu Get Selected Item via Command [duplicate]

问题

I have this View:

<StackPanel>
<StackPanel.DataContext>
    <local:MainViewModel />
</StackPanel.DataContext>
<ListView ItemsSource="{Binding Persons}" x:Name="xamlPersonList">
    <ListBox.ContextMenu>
        <ContextMenu>
            <MenuItem Header="EMail" Command="{Binding WriteMailCommand}" CommandParameter="{Binding ElementName=xamlPersonList,Path=SelectedItem}" />
        </ContextMenu>
    </ListBox.ContextMenu>
</ListView>
</StackPanel>

I want to get the selected item (or the clicked item) and do some stuff with it inside my Command-Method. This is my Ctor and Command-Method of my ViewModel:

public ICommand WriteMailCommand { get; private set; }
public MainViewModel()
{
    _persons = new ObservableCollection<Person>();
    for (int i = 0; i < 10; i++)
    {
        _persons.Add(new Person()
        {
            ID = i,
            Name = "Robert " + i
        });
    }

    WriteMailCommand = new RelayCommand<object>(WriteMailMethod);
}

private void WriteMailMethod(object obj)
{
}

The obj parameter is always null. I don't know what I am missing here?! I tried this solution: How to pass listbox selecteditem as command parameter in a button?

回答1:

The binding isn't working because the ContextMenu exists outside of your control's visual tree, and so it's impossible for it to find the ListBox. In fact I'm surprised it's invoking your command without the usual incantation to get the data context of the associated control:

<ContextMenu DataContext="{Binding PlacementTarget.DataContext, RelativeSource={RelativeSource Self}}" >

Regardless, you can use the answer suggested here, or I can suggest an alternate implementation: add a SelectedPerson property to your view-model:

private Person selectedPerson;
public Person SelectedPerson 
{ 
    get { return selectedPerson; } 
    set
    {
        selectedPerson = value;
        RaisePropertyChanged(); // or whatever your implementation is
    }
}

Your XAML would be simple, too:

<ListView ItemsSource="{Binding Persons}" 
          SelectedItem="{Binding SelectedPerson}">
    <ListBox.ContextMenu>
        <ContextMenu>
            <MenuItem Header="EMail" 
                      Command="{Binding WriteMailCommand}" 
                      CommandParameter="{Binding SelectedPerson}" />
        </ContextMenu>
    </ListBox.ContextMenu>
</ListView>

来源：https://stackoverflow.com/questions/33548871/listbox-contextmenu-get-selected-item-via-command

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