因此，我尝试通过Command将MyProperty从View的代码隐藏传递到ViewModel。它看起来像这样：

视图：code-behind .xaml.cs

public partial class MainWindow : Window
{
    public string MyProperty { get; set; }
    
    public MainWindow()
    {
        InitializeComponent();
    }

    private void Test_Click(object sender, RoutedEventArgs e)
    {
        MyProperty = "test click";
    }
}

字符串

视图：.xaml

<MenuItem Header="Test" CommandParameter="{Binding ElementName=MainWindow, Path=MyProperty}" Command="{Binding Test}"  Click="Test_Click"></MenuItem>

型

ViewModel：

private RelayCommand _test;

public RelayCommand Test { 
    get 
    {
        if (_test != null)
        {
            return _test;
        }

        return _test = new RelayCommand(obj =>
        {
            MessageBox.Show($"{obj}"); // here obj = null why? 
        });
    }
}

型

RelayCommand：

internal class RelayCommand : ICommand
{
    private Action<object> _execute;
    private Func<object, bool> _canExecute;

    public event EventHandler CanExecuteChanged
    {
        add { CommandManager.RequerySuggested += value; }
        remove { CommandManager.RequerySuggested -= value; }
    }

    public RelayCommand(Action<object> execute, Func<object, bool> canExecute = null)
    {
        _execute = execute;
        _canExecute = canExecute;
    }

    public bool CanExecute(object parameter)
    {
        return _canExecute == null || _canExecute(parameter);
    }

    public void Execute(object parameter)
    {
        _execute(parameter);
    }
}

型
我也试过使用RelativeSource代替ElementName，但不起作用：

<MenuItem Command="{Binding DataContext.Test, RelativeSource={RelativeSource AncestorType=views:MainWindow}}" CommandParameter="{Binding RelativeSource={RelativeSource AncestorType=views:MainWindow}, Path=MyProp}" Click="Test_Click"></MenuItem>

型
我的问题是：
1.为什么它不工作？
1.哪种约束力？当我首先运行调试时，将Event_Click，然后CanExecute，然后Execute -这里MyProperty已经从Event_Click设置，但无论如何命令都为空。