从映像实例获取原始数据

创建一个筛选器流,该流将通过要附加到的流,但在流本身关闭时不关闭该流:

public class AppendingStream : Stream
{
    private readonly long _startPos;
    private readonly Stream _sink;
    public AppendingStream(Stream sink)
    {
        if(sink == null)
            throw new ArgumentNullException();
        if(!sink.CanWrite)
            throw new ArgumentException();
        _sink = sink;
        try
        {
            _startPos = sink.Position;
        }
        catch(NotSupportedException)
        {
            _startPos = -1;
        }
    }
    public override bool CanRead
    {
        get
        {
            return false;
        }
    }
    public override bool CanSeek
    {
        get
        {
            return _sink.CanSeek && _startPos != -1;
        }
    }
    public override bool CanTimeout
    {
        get
        {
            return _sink.CanTimeout;
        }
    }
    public override bool CanWrite
    {
        get
        {
            return true;
        }
    }
    public override long Length
    {
        get
        {
            if(_startPos == -1)
                throw new NotSupportedException();
            return _sink.Length - _startPos;
        }
    }
    public override long Position
    {
        get
        {
            return _sink.Position - _startPos;
        }
        set
        {
            _sink.Position = value + _startPos;
        }
    }
    public override void Flush()
    {
        _sink.Flush();
    }
    public override int Read(byte[] buffer, int offset, int count)
    {
        throw new NotSupportedException();
    }
    public override int ReadByte()
    {
        throw new NotSupportedException();
    }
    public override long Seek(long offset, SeekOrigin origin)
    {
        if(origin == SeekOrigin.Begin)
            return _sink.Seek(offset + _startPos, SeekOrigin.Begin) - _startPos;
        else
            return _sink.Seek(offset, origin);
    }
    public override void SetLength(long value)
    {
        if(_startPos == -1)
            throw new NotSupportedException();
        _sink.SetLength(value + _startPos);
    }
    public override void Write(byte[] buffer, int offset, int count)
    {
        _sink.Write(buffer, offset, count);
    }
    public override void WriteByte(byte value)
    {
        _sink.WriteByte(value);
    }
}

然后你就不再有关闭流的问题了,因为这无关紧要。

处理寻找新位置的位是因为某些图像格式是以非顺序方式写入的。如果底层流不支持它,它将不起作用,但无论如何,这也不会起作用。