c# – 如何从后台线程中使用FixedDocument？

2019年7月28日 277次阅读

当所有内容都在同一个线程上时,以下代码可以正常工作.但是,在后台线程上创建FixedDocument时,将PrintPreview移动到UI线程,我得到：

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

问题在于：

writer.Write(fixeddocument.DocumentPaginator);

我无法获得Dispatcher.invoke / begininvoke – 或其他任何东西来解决这个问题.

那么如何将另一个线程的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,我已经Google搜索了几个小时而没有找到任何解决方案.如果有,我错过了它).

我一直认为我必须将PrintPreview保持在与FixedDocument相同的线程中 – 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();
    }
}

最佳答案 它显然是你方法中的静态修饰符.将其更改为实例方法可以促进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();
        }
    }
}
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