c# - 如何从后台线程使用 FixedDocument？

Question

当一切都在同一个线程上时，以下代码可以正常工作。但是，当在后台线程上创建 FixedDocument 时将 PrintPreview 移动到 UI 线程时，我得到:

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

问题行是:

writer.Write(fixeddocument.DocumentPaginator);

我无法获取 Dispatcher.invoke/begininvoke —— 或任何其他解决此问题的方法。

那么如何将来自另一个线程的 FixedDocument 带到 UI 线程呢？

(请注意，FixedDocument 需要几分钟才能生成，因此必须在后台线程上创建。是的，我用 Google 搜索了几个小时但没有找到任何解决方案。如果有的话，我错过了)。

我一直在想，我必须将 PrintPreview 与 FixedDocument 保持在同一个线程中——我希望不会。

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

    MemoryStream ms = new MemoryStream();

    using (Package p = Package.Open(ms, FileMode.Create, FileAccess.ReadWrite))
    {
        Uri u = new Uri("pack://TemporaryPackageUri.xps");
        PackageStore.AddPackage(u, p);

        XpsDocument doc = new XpsDocument(p, CompressionOption.Maximum, u.AbsoluteUri);

        XpsDocumentWriter writer = XpsDocument.CreateXpsDocumentWriter(doc);

        writer.Write(fixeddocument.DocumentPaginator);

        FixedDocumentSequence fixedDocumentSequence = doc.GetFixedDocumentSequence();

        var previewWindow = new PrintPreview(fixedDocumentSequence);

        Action closeAction = () => previewWindow.Close();

        ct.Register(() =>
              previewWindow.Dispatcher.Invoke(closeAction) 
        );

       previewWindow.ShowDialog();  

        PackageStore.RemovePackage(u);
        doc.Close();
    }
}

Answer 1

这显然是您方法中的 static 修饰符。将其更改为实例方法可以让您方便 Dispatcher:

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();

    }

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


        MemoryStream ms = new MemoryStream();

        using (Package p = Package.Open(ms, FileMode.Create, FileAccess.ReadWrite))
        {
            Uri u = new Uri("pack://TemporaryPackageUri.xps");
            PackageStore.AddPackage(u, p);

            XpsDocument doc = new XpsDocument(p, CompressionOption.Maximum, u.AbsoluteUri);

            XpsDocumentWriter writer = XpsDocument.CreateXpsDocumentWriter(doc);

            //writer.Write(fixeddocument.DocumentPaginator);
            Dispatcher.Invoke(new Action<DocumentPaginator>(writer.Write), fixeddocument.DocumentPaginator);

            FixedDocumentSequence fixedDocumentSequence = doc.GetFixedDocumentSequence();

            var previewWindow = new PrintPreview(fixedDocumentSequence);

            Action closeAction = () => previewWindow.Close();

            ct.Register(() =>
                  previewWindow.Dispatcher.Invoke(closeAction)
            );

            previewWindow.ShowDialog();

            PackageStore.RemovePackage(u);
            doc.Close();
        }
    }
}