C# 如何合并两个内存流？

How to merge two memory streams?

提问by SaneDeveloper

I have two MemoryStream instances.

我有两个 MemoryStream 实例。

How to merge them into one instance?

如何将它们合并为一个实例？

Well, now I can't copy from one MemoryStream to another. Here is a method:

好吧，现在我无法从一个 MemoryStream 复制到另一个。这是一个方法：

public static Stream ZipFiles(IEnumerable<FileToZip> filesToZip) {
ZipStorer storer = null;
        MemoryStream result = null;
        try {
            MemoryStream memory = new MemoryStream(1024);
            storer = ZipStorer.Create(memory, GetDateTimeInRuFormat());
            foreach (var currentFilePath in filesToZip) {
                string fileName = Path.GetFileName(currentFilePath.FullPath);
                storer.AddFile(ZipStorer.Compression.Deflate, currentFilePath.FullPath, fileName,
                               GetDateTimeInRuFormat());
            }
            result = new MemoryStream((int) storer.ZipFileStream.Length);
            storer.ZipFileStream.CopyTo(result); //Does not work! 
                                               //result's length will be zero
        }
        catch (Exception) {
        }
        finally {
            if (storer != null)
                storer.Close();
        }
        return result;
    }

采纳答案by illegal-immigrant

Spectacularly easy with CopyToor CopyToAsync:

使用CopyTo或CopyToAsync非常简单：

var streamOne = new MemoryStream();
FillThisStreamUp(streamOne);
var streamTwo = new MemoryStream();
DoSomethingToThisStreamLol(streamTwo);
streamTwo.CopyTo(streamOne); // streamOne holds the contents of both

The framework, people. The framework.

框架，人。该框架。

回答by illegal-immigrant

• Create third(let it be mergedStream) MemoryStreamwith length equal to sum of first and second lengths

• Write first MemoryStreamto mergedStream(use GetBuffer()to get byte[]from MemoryStream)

• Write second MemoryStreamto mergedStream(use GetBuffer())

• Remember about offset while writing.

• 创建第三个（让它成为mergedStream）MemoryStream，其长度等于第一个和第二个长度的总和

• 先写MemoryStream到mergedStream（使用GetBuffer()获得byte[]从MemoryStream）

• 写第二个MemoryStream到mergedStream（使用GetBuffer()）

• 在写作时记住偏移量。

It's rather append, but it's totally unclear what is merge operation on MemoryStreams

它是append，但完全不清楚 MemoryStreams 上的合并操作是什么

回答by Amit

Based on the answer shared by @Will above, here is complete code:

根据上面@Will 分享的答案，这里是完整的代码：

void Main()
{
    var s1 = GetStreamFromString("Hello");
    var s2 = GetStreamFromString(" World");

    var s3 = s1.Append(s2);
    Console.WriteLine(Encoding.UTF8.GetString((s3 as MemoryStream).ToArray()));
}

public static Stream GetStreamFromString(string text)
{
        MemoryStream stream = new MemoryStream();
        StreamWriter writer = new StreamWriter(stream);
        writer.Write(text);
        writer.Flush();
        stream.Position = 0;

        return stream;
}

public static class Extensions
{ 
    public static Stream Append(this Stream destination, Stream source)
    {
        destination.Position = destination.Length;
        source.CopyTo(destination);

        return destination;
    }
}

And merging stream collection with async:

并将流集合与async：

async Task Main()
{
    var list = new List<Task<Stream>> { GetStreamFromStringAsync("Hello"), GetStreamFromStringAsync(" World") };

    Stream stream = await list
            .Select(async item => await item)
            .Aggregate((current, next) => Task.FromResult(current.Result.Append(next.Result)));

    Console.WriteLine(Encoding.UTF8.GetString((stream as MemoryStream).ToArray()));
}

public static Task<Stream> GetStreamFromStringAsync(string text)
{
    MemoryStream stream = new MemoryStream();
    StreamWriter writer = new StreamWriter(stream);
    writer.Write(text);
    writer.Flush();
    stream.Position = 0;

    return Task.FromResult(stream as Stream);
}

public static class Extensions
{
    public static Stream Append(this Stream destination, Stream source)
    {
        destination.Position = destination.Length;
        source.CopyTo(destination);

        return destination;
    }
}