WPF绑定事件在关闭窗口后发生

我有一个愚蠢的问题，我敢肯定会遇到很多人。但是，我无法找到令人满意的解决方案。

考虑简单的项目（请参见下面的代码）。当我在字段中键入文本，然后单击[x]以关闭窗口时，更改将VeryImportantProperty在窗口的Closing事件之后发生。结果，窗口关闭而不要求保存更改。

是否有已知的解决方法或更好的编程技术？我发现的唯一建议是，通过启动优先级较低的子同步线程（不执行任何操作）来延迟关闭处理程序。但是，这并没有太大作用，因为绑定和关闭事件处理程序在同一线程中运行。

C＃：

    namespace CloseRequestTestProject {

    public class MyViewModel : INotifyPropertyChanged {
        public MyViewModel() { _isDirty = false; _veryImportantProperty = "Change me!"; }
        public event PropertyChangedEventHandler PropertyChanged;
        protected virtual void OnPropertyChanged(string propertyName) {
            PropertyChangedEventHandler handler = this.PropertyChanged;
            if (handler != null) {
                var e = new PropertyChangedEventArgs(propertyName);
                handler(this, e);
            }
        }

        private bool _isDirty;
        private string _veryImportantProperty;
        public string VeryImportantProperty {
            get { return _veryImportantProperty; }
            set {
                if (value != _veryImportantProperty) {
                    Trace.TraceWarning("Binding event!");
                    Trace.TraceWarning("ThreadId is " + System.Threading.Thread.CurrentThread.ManagedThreadId.ToString());
                    _isDirty = true;
                    _veryImportantProperty = value;
                    OnPropertyChanged("VeryImportantProperty");
                }
            }
        }

        public void viewIsClosing(object sender, CancelEventArgs e) {
            Trace.TraceWarning("View is closing");
            Trace.TraceWarning("ThreadId is " + System.Threading.Thread.CurrentThread.ManagedThreadId.ToString());
            if (_isDirty) {
                switch (MessageBox.Show("VeryImportantProperty has changed. Save changes?", "Question", MessageBoxButton.YesNoCancel, MessageBoxImage.Warning)) {
                    case MessageBoxResult.Yes: ; break;
                    case MessageBoxResult.No: ; break;
                    default: e.Cancel = true; break;
                }
            }
        }
    }

    public partial class MainWindow : Window {
        public MainWindow() {
            InitializeComponent();
            MyViewModel vm = new MyViewModel();
            DataContext = vm;
            Closing += vm.viewIsClosing;
        }

    }
}

XAML：

    <Window x:Class="CloseRequestTestProject.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <WrapPanel>
            <TextBlock Text="Very Important Property" VerticalAlignment="Top" Margin="10"/>
            <TextBox Text="{Binding VeryImportantProperty}" VerticalAlignment="Top" Margin="10" MinWidth="200"/>
        </WrapPanel>

    </Grid>
</Window>