编写自定义的Stream
派生类并不难,但在这种情况下具有挑战性的部分是需要Encoding
支持。以下是只读前向实现,当需要时使用小缓冲区适合一个完整的字符字节:
public static class StringUtils
{
public static Stream AsStream(this string source, Encoding encoding = null)
{
return string.IsNullOrEmpty(source) ? Stream.Null : new StringStream(source, encoding ?? Encoding.UTF8);
}
class StringStream : Stream
{
string source;
Encoding encoding;
int position, length;
int charPosition;
int maxBytesPerChar;
byte[] encodeBuffer;
int encodeOffset, encodeCount;
internal StringStream(string source, Encoding encoding)
{
this.source = source;
this.encoding = encoding;
length = encoding.GetByteCount(source);
maxBytesPerChar = encoding.GetMaxByteCount(1);
}
public override bool CanRead { get { return true; } }
public override bool CanSeek { get { return false; } }
public override bool CanWrite { get { return false; } }
public override long Length { get { return length; } }
public override void SetLength(long value) { throw new NotSupportedException(); }
public override long Position { get { return position; } set { throw new NotSupportedException(); } }
public override long Seek(long offset, SeekOrigin origin) { throw new NotSupportedException(); }
public override void Write(byte[] buffer, int offset, int count) { throw new NotSupportedException(); }
public override void Flush() { }
public override int Read(byte[] buffer, int offset, int count)
{
int readCount = 0;
for (int byteCount; readCount < count && position < length; position += byteCount, readCount += byteCount)
{
if (encodeCount == 0)
{
int charCount = Math.Min((count - readCount) / maxBytesPerChar, source.Length - charPosition);
if (charCount > 0)
{
byteCount = encoding.GetBytes(source, charPosition, charCount, buffer, offset + readCount);
Debug.Assert(byteCount > 0 && byteCount <= (count - readCount));
charPosition += charCount;
continue;
}
if (encodeBuffer == null) encodeBuffer = new byte[maxBytesPerChar];
encodeCount = encoding.GetBytes(source, charPosition, 1, encodeBuffer, encodeOffset = 0);
Debug.Assert(encodeCount > 0);
}
byteCount = Math.Min(encodeCount, count - readCount);
for (int i = 0; i < byteCount; i++)
buffer[offset + readCount + i] = encodeBuffer[encodeOffset + i];
encodeOffset += byteCount;
if ((encodeCount -= byteCount) == 0) charPosition++;
}
return readCount;
}
}
}
Read
还是你也需要Seek
?我猜想不需要Write
(所以我对你的问题中建议使用StreamWriter
感到惊讶),因为字符串是不可变的。 - Damien_The_Unbeliever