c# - .NET GZipStream 解压缩生成空流

Question

我正在尝试序列化和压缩 WPF FlowDocument ，然后执行相反的操作 - 解压缩字节数组并反序列化以重新创建 FlowDocument - 使用 .NET GZipStream类(class)。我正在按照 MSDN 上描述的示例进行操作，并且我有以下测试程序:

var flowDocumentIn = new FlowDocument();
flowDocumentIn.Blocks.Add(new Paragraph(new Run("Hello")));
Debug.WriteLine("Compress");
byte[] compressedData;
using (var uncompressed = new MemoryStream())
{
    XamlWriter.Save(flowDocumentIn, uncompressed);
    uncompressed.Position = 0;
    using (var compressed = new MemoryStream())
    using (var compressor = new GZipStream(compressed, CompressionMode.Compress))
    {
        Debug.WriteLine(" uncompressed.Length: " + uncompressed.Length);
        uncompressed.CopyTo(compressor);
        Debug.WriteLine(" compressed.Length: " + compressed.Length);
        compressedData = compressed.ToArray();
    }
}

Debug.WriteLine("Decompress");
FlowDocument flowDocumentOut;
using (var compressed = new MemoryStream(compressedData))
using (var uncompressed = new MemoryStream())
using (var decompressor = new GZipStream(compressed, CompressionMode.Decompress))
{
    Debug.WriteLine(" compressed.Length: " + compressed.Length);
    decompressor.CopyTo(uncompressed);
    Debug.WriteLine(" uncompressed.Length: " + uncompressed.Length);
    flowDocumentOut = (FlowDocument) XamlReader.Load(uncompressed);
}

Assert.AreEqual(flowDocumentIn, flowDocumentOut);

但是我在 XamlReader.Load 行遇到异常，这是正常的，因为调试输出表明未压缩流的长度为零。

Compress
 uncompressed.Length: 123
 compressed.Length: 202
Decompress
 compressed.Length: 202
 uncompressed.Length: 0

为什么最终的未压缩流不包含原始的 123 个字节？

(请忽略“压缩”字节数组比“未压缩”字节数组大的事实——我通常会处理更大的流文档)

Answer 1

在从内存流中获取压缩字节之前，您需要关闭GZipStream。在这种情况下，关闭由因使用而调用的 Dispose 处理。

using (var compressed = new MemoryStream())
{
    using (var compressor = new GZipStream(compressed, CompressionMode.Compress))
    {
        uncompressed.CopyTo(compressor);
    }
    // Get the compressed bytes only after closing the GZipStream
    compressedBytes = compressed.ToArray();
}

这行得通，您甚至可以删除 MemoryStream 的 using，因为它将由 GZipStream 处理，除非您使用构造函数重载这允许您指定底层流应该保持打开状态。这意味着您正在使用该代码在已处置的流上调用 ToArray 但这是允许的，因为字节仍然可用，这使得处置内存流有点奇怪，但如果您不这样做，FXCop 会惹恼您.