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());
    }
}

事情是resultStream总是空的！

我在这里做错了什么？

Answer 1

将您的验证WriteLine放在使用之外。缓冲区尚未刷新。

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);

除此之外，你不需要在写作线上的所有ToString()。

PS：所有BinaryFormatter都使用字符串写入带有长度前缀的字节。如果你不需要前缀（我的猜测），它可能会变成：

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();
}

反过来也很简单，但你需要估计最大长度来创建读缓冲区：

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DeflateStream在关闭之前不会将数据刷新到基础流。关闭后，resultStream将包含压缩数据。请注意，默认情况下，DeflateStream会在基础流关闭时关闭它，但您不希望这样，因此您需要为true参数传递leaveOpen。此外，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（我没有足够的学分投票）

将控件WriteLine置于使用
之外

这是不完整和误导性的。一旦DeflateStream超出范围，DeflateStream就会关闭底层的resultStream。因此resultStream.Length抛出

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

Thomas Levesque是正确的=＆gt;同时将leaveOpen设置为true。

一个有趣的问题，HH和TL提出了一些好的观点。

DeflateStream不能在MemoryStream上运行？

3 个答案: