DeflateStream不在MemoryStream上工作吗？

Question

我有以下代码：

MemoryStream resultStream = new MemoryStream();
string users = ""//Really long string goes here
BinaryFormatter bFormatter = new BinaryFormatter();
using (MemoryStream assignedUsersStream = new MemoryStream())
{
    bFormatter.Serialize(assignedUsersStream, users);
    assignedUsersStream.Position = 0;

    using (var compressionStream =
        new DeflateStream(resultStream, CompressionLevel.Optimal))
    {
        assignedUsersStream.CopyTo(compressionStream);

        Console.WriteLine("Compressed from {0} to {1} bytes.",
            assignedUsersStream.Length.ToString(),
            resultStream.Length.ToString());
    }
}            

问题是resultStream总是空的！

我在这里做错什么了？

Answer 1

将您的验证WriteLine放在使用之外。缓冲器还没冲过。

using (DeflateStream compressionStream = new DeflateStream(resultStream, CompressionLevel.Optimal))
{
    assignedUsersStream.CopyTo(compressionStream);

    //Console.WriteLine("Compressed from {0} to {1} bytes.",
    //       assignedUsersStream.Length.ToString(), resultStream.Length.ToString());
}

Console.WriteLine("Compressed from {0} to {1} bytes.",
     assignedUsersStream.Length, resultStream.ToArray().Length);

此外，你不需要所有的ToString()在一个书面形式。

PS: BinaryFormatter对字符串所做的一切就是用长度前缀写入字节。如果您不需要前缀(我猜)，它可能变成：

string users = "";//Really long string goes here
byte[] result;  

using (MemoryStream resultStream = new MemoryStream())
{
    using (DeflateStream compressionStream = new DeflateStream(resultStream,
             CompressionLevel.Optimal))
    {
        byte[] inBuffer = Encoding.UTF8.GetBytes(users);
        compressionStream.Write(inBuffer, 0, inBuffer.Length);
    }
    result = resultStream.ToArray();
}

相反的操作也同样容易，但是您需要估计最大长度才能创建读取缓冲区：

string users2 = null;

using (MemoryStream resultStream = new MemoryStream(result))
{
    using (DeflateStream compressionStream = new  DeflateStream(resultStream,
            CompressionMode.Decompress))
    {
        byte[] outBuffer = new byte[2048];   // need an estimate here
        int length = compressionStream.Read(outBuffer, 0, outBuffer.Length);
        users2 = Encoding.UTF8.GetString(outBuffer, 0, length);                        
    }                    
}

Answer 2

这是因为在数据关闭之前，DeflateStream不会将数据刷新到底层流。关闭后，resultStream将包含压缩数据。注意，默认情况下，当底层流关闭时，DeflateStream会关闭它，但是您不想这样做，所以您需要为leaveOpen参数传递true。另外，您不需要2个内存流，您可以直接序列化到compressionStream

    string users = ""; //Really long string goes here
    BinaryFormatter bFormatter = new BinaryFormatter();
    using (MemoryStream resultStream = new MemoryStream())
    {
        using (DeflateStream compressionStream = new DeflateStream(resultStream, CompressionLevel.Optimal, true))
        {
            bFormatter.Serialize(compressionStream, users);
            Console.WriteLine(resultStream.Length); // 0 at this point
        }
        Console.WriteLine(resultStream.Length); // now contains the actual length
    } 

Answer 3

从最初的答案来看(我没有足够的学分去投票)

将您的控件WriteLine放在使用

，这是不完整的，因此海事组织误导了。DeflateStream的Dispose(bool) implementation Close是垃圾收集后DeflateStream被Finalized时的底层resultStream。当这种情况发生时，resultStream.Length会抛出：

Unhandled Exception: System.ObjectDisposedException: Cannot access a closed Stream.

换句话说，Thomas的注释是至关重要的：还将设置为 true.

这是一个有趣的问题，有HH和TL提出的一些好的观点。