c# – 如何使用CancellationTokenSource关闭另一个线程上的对话

我试图更好地理解CancellationTokenSource模型以及如何跨线程边界使用它.

我有一个主窗口(在UI线程上)后面的代码：

public MainWindow()
        {
            InitializeComponent();

            Loaded += (s,e) => {
                DataContext = new MainWindowViewModel();
                Closing += ((MainWindowViewModel)DataContext).MainWindow_Closing;

            };
        }

它在关闭时正确调用CloseWindow代码：

private void CloseWindow(IClosable window)
        {
            if (window != null)
            {
                windowClosingCTS.Cancel();
                window.Close();
            }
        }

通过选择菜单项,在后台线程上创建第二个窗口：

// Print Preview
    public static void PrintPreview(FixedDocument fixeddocument,CancellationToken ct)
    {
        // Was cancellation already requested? 
        if (ct.IsCancellationRequested)
              ct.ThrowIfCancellationRequested();

               ............................... 

            // Use my custom document viewer (the print button is removed).
            var previewWindow = new PrintPreview(fixedDocumentSequence);

            //Register the cancellation procedure with the cancellation token
            ct.Register(() => 
                   previewWindow.Close() 
            );

            previewWindow.ShowDialog();

        }
    }

在MainWindowViewModel(在UI线程上),我把：

public CancellationTokenSource windowClosingCTS { get; set; }

其构造函数为：

// Constructor
    public MainMenu()
    {
        readers = new List<Reader>();
        CloseWindowCommand = new RelayCommand<IClosable>(this.CloseWindow);
        windowClosingCTS = new CancellationTokenSource();
    }

现在我的问题.当关闭UI线程上的MainWindow时,windowClosingCTS.Cancel()会立即调用使用ct注册的委托,即调用previewWindow.Close().这现在立即返回到“If(Windows！= null)：

“The calling thread cannot access this object because a different
thread owns it.”

那么我做错了什么？