无法在自定义TextBox的EventTrigger上从CallMethodAction调用方法

<TextBox>
    <i:Interaction.Triggers>
        <i:EventTrigger EventName="LostFocus">
            <i:InvokeCommandAction Command="{Binding LostFocusCommand}" />
        </i:EventTrigger>
    </i:Interaction.Triggers>
</TextBox>

public class MyViewModel : INotifyPropertyChanged
{
    public ICommand LostFocusCommand { get; private set; }

    public MyViewModel()
    {
        LostFocusCommand = new RelayCommand(LostFocus);
    }

    private void LostFocus()
    {
        // 调用所需的方法
    }
}

public partial class MyPage : Page
{
    public MyPage()
    {
        InitializeComponent();
        DataContext = new MyViewModel();
    }
}