如何从字符串生成流？

Question

我需要为一个方法编写单元测试,该方法接受来自文本文件的流.我想做这样的事情:

Stream s = GenerateStreamFromString("a,b \n c,d");

Answer 1

public static Stream GenerateStreamFromString(string s)
{
    var stream = new MemoryStream();
    var writer = new StreamWriter(stream);
    writer.Write(s);
    writer.Flush();
    stream.Position = 0;
    return stream;
}

别忘了使用:

using (var stream = GenerateStreamFromString("a,b \n c,d"))
{
    // ... Do stuff to stream
}

关于StreamWriter不被处置.StreamWriter它只是基本流的包装器,不使用任何需要处理的资源.该Dispose方法将关闭底层Stream是StreamWriter被写入.在这种情况下,MemoryStream我们想要返回.

在.NET 4.5中,现在有一个重载,StreamWriter它可以在编写器被处理后保持底层流的打开,但是这个代码也做同样的事情并且也适用于其他版本的.NET.

请参阅是否有任何方法可以在不关闭其BaseStream的情况下关闭StreamWriter？

Answer 2

另一种方案:

public static MemoryStream GenerateStreamFromString(string value)
{
    return new MemoryStream(Encoding.UTF8.GetBytes(value ?? ""));
}

Answer 3

将其添加到静态字符串实用程序类:

public static Stream ToStream(this string str)
{
    MemoryStream stream = new MemoryStream();
    StreamWriter writer = new StreamWriter(stream);
    writer.Write(str);
    writer.Flush();
    stream.Position = 0;
    return stream;
}

这会添加一个扩展功能,您可以简单地:

using (var stringStream = "My string".ToStream())
{
    // use stringStream
}

Answer 4

public Stream GenerateStreamFromString(string s)
{
    return new MemoryStream(Encoding.UTF8.GetBytes(s));
}

Answer 5

使用MemoryStream该类,首先调用Encoding.GetBytes将字符串转换为字节数组.

你随后需要一个TextReader流吗？如果是这样,你可以提供一个StringReader直接,绕过MemoryStream和Encoding步骤.

Answer 6

我使用了这样的答案:

public static Stream ToStream(this string str, Encoding enc = null)
{
    enc = enc ?? Encoding.UTF8;
    return new MemoryStream(enc.GetBytes(str ?? ""));
}

然后我像这样使用它:

String someStr="This is a Test";
Encoding enc = getEncodingFromSomeWhere();
using (Stream stream = someStr.ToStream(enc))
{
    // Do something with the stream....
}

Answer 7

我们使用下面列出的扩展方法.我认为你应该让开发人员对编码做出决定,因此所涉及的魔法就更少了.

public static class StringExtensions {

    public static Stream ToStream(this string s) {
        return s.ToStream(Encoding.UTF8);
    }

    public static Stream ToStream(this string s, Encoding encoding) {
        return new MemoryStream(encoding.GetBytes(s ?? ""));
    }
}

Answer 8

干得好:

private Stream GenerateStreamFromString(String p)
{
    Byte[] bytes = UTF8Encoding.GetBytes(p);
    MemoryStream strm = new MemoryStream();
    strm.Write(bytes, 0, bytes.Length);
    return strm;
}

Answer 9

扩展方法的现代化版本和稍作修改的版本ToStream：

public static Stream ToStream(this string value) => ToStream(value, Encoding.UTF8);

public static Stream ToStream(this string value, Encoding encoding) 
                          => new MemoryStream(encoding.GetBytes(value ?? string.Empty));

@Shane Bowe答案的@Palec评论中建议的修改。

Answer 10

我想你可以从使用MemoryStream中受益.您可以使用Encoding类的GetBytes方法填充您获得的字符串字节.

Answer 11

如果您需要更改编码，我会为@ShaunBowe的解决方案投票。但是这里的每个答案至少将整个字符串复制到内存中一次。ToCharArray+BlockCopy组合的答案做两次。

如果这很重要，这里是Stream原始 UTF-16 字符串的简单包装器。如果与StreamReaderselect 一起Encoding.Unicode使用：

public class StringStream : Stream
{
    private readonly string str;

    public override bool CanRead => true;
    public override bool CanSeek => true;
    public override bool CanWrite => false;
    public override long Length => str.Length * 2;
    public override long Position { get; set; } // TODO: bounds check

    public StringStream(string s) => str = s ?? throw new ArgumentNullException(nameof(s));

    public override long Seek(long offset, SeekOrigin origin)
    {
        switch (origin)
        {
            case SeekOrigin.Begin:
                Position = offset;
                break;
            case SeekOrigin.Current:
                Position += offset;
                break;
            case SeekOrigin.End:
                Position = Length - offset;
                break;
        }

        return Position;
    }

    private byte this[int i] => (i & 1) == 0 ? (byte)(str[i / 2] & 0xFF) : (byte)(str[i / 2] >> 8);

    public override int Read(byte[] buffer, int offset, int count)
    {
        // TODO: bounds check
        var len = Math.Min(count, Length - Position);
        for (int i = 0; i < len; i++)
            buffer[offset++] = this[(int)(Position++)];
        return (int)len;
    }

    public override int ReadByte() => Position >= Length ? -1 : this[(int)Position++];
    public override void Flush() { }
    public override void SetLength(long value) => throw new NotSupportedException();
    public override void Write(byte[] buffer, int offset, int count) => throw new NotSupportedException();
    public override string ToString() => str; // ;)     
}

而这里是必要的约束检查一个更完整的解决方案（源自MemoryStream因此它具有ToArray和WriteTo方法以及）。

Answer 12

现在使用 C# 11，我们可以用一行完成此操作：

var ms = new MemoryStream("some string"u8.ToArray());

有关 Utf8 字符串文字的详细信息可以在此处找到https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/csharp-11.0/utf8-string-literals#detailed-design