如何从字节数组创建 XpsDocument？

Question

I would like to create a new System.Windows.Xps.Packaging.XpsDocument object from byte array, as I will not want to store it immediately on a local machine.

By using a temp file it works fine:

public static XpsDocument OpenXpsDocument(string url)
{
    WebClient webClient = new System.Net.WebClient();
    byte[] data = webClient.DownloadData(url);

    using (BinaryWriter writer = new System.IO.BinaryWriter(File.OpenWrite(xpsTempFilePath)))
    {
        writer.Write(data);
        writer.Flush();
    }

    XpsDocument xpsDocument = new System.Windows.Xps.Packaging.XpsDocument(xpsTempFilePath, FileAccess.Read);
    return xpsDocument;
}

However, what I want to accomplish is more like this:

public static XpsDocument OpenXpsDocument(string url)
{
    WebClient webClient = new WebClient();
    byte[] data = webClient.DownloadData(url);
    Package package;
    using (Stream stream = new MemoryStream(data))
    {
        package = System.IO.Packaging.Package.Open(stream);
    }
    XpsDocument xpsDocument = new XpsDocument(package, CompressionOption.SuperFast, url);
    return xpsDocument;
}

Usage of the aforementioned methods goes like that:

XpsDocument xps = TaxReturnCreator.OpenXpsDocument(tempFileUrl);
documentViewer1.Document = xps.GetFixedDocumentSequence();

And, using the last-described method of trying to display the XPS content in a WPF window (without saving) crashes with a System.ObjectDisposedException ("Cannot access a closed Stream") (First method works fine).

Am I supposed to still keep the Stream open after creating the XpsDocument or am I missing something else? Maybe someone knows a completely different / better method of retrieving XPS data as bytes over network and creating an XpsDocument object from the data?

Answer 1

You cannot close a stream backing an XpsDocument. You must allow the Package to manage the backing MemoryStream, which will be collected once this Package is collected. It may seem a bit of a heresy to do the following:

public static XpsDocument OpenXpsDocument(string url)
{
    var webClient = new WebClient();
    var data = webClient.DownloadData(url);
    var package = System.IO.Packaging.Package.Open(new MemoryStream(data));
    var xpsDocument = new XpsDocument(package, 
                                      CompressionOption.SuperFast, 
                                      url);
    return xpsDocument;
}

but it is how this must be done.

Answer 2

You should try including

XpsDocument xpsDocument = new XpsDocument(package, CompressionOption.SuperFast, url);

into using block, ie

Package package;
using (Stream stream = new MemoryStream(data))
{
    package = System.IO.Packaging.Package.Open(stream);
    XpsDocument xpsDocument = new XpsDocument(package, CompressionOption.SuperFast, url);
}
return xpsDocument;