c# - 使用 VirtualFileDataObject 使用 IStream 拖放大型虚拟文件

Question

我成功地使用了 VirtualFileDataObject code from Delay's blog ，但我想避免将整个文件流式传输到内存中。

我在 Stack Overflow Drag and Drop large virtual files from c# to Windows Explorer 上发现了这个之前回答过的问题matthieu 通过更改 SetData 方法的签名回答了这个问题。

这是我的问题，在更改了 SetData 方法的签名后，其他调用它的地方仍然在寻找旧的签名。

这里是原始的SetData；

   public void SetData(short dataFormat, int index, Action<Stream> streamData)
    {
        _dataObjects.Add(
            new DataObject
            {
                FORMATETC = new FORMATETC
                {
                    cfFormat = dataFormat,
                    ptd = IntPtr.Zero,
                    dwAspect = DVASPECT.DVASPECT_CONTENT,
                    lindex = index,
                    tymed = TYMED.TYMED_ISTREAM
                },
                GetData = () =>
                {
                    // Create IStream for data
                    var ptr = IntPtr.Zero;
                    var iStream = NativeMethods.CreateStreamOnHGlobal(IntPtr.Zero, true);
                    if (streamData != null)
                    {
                        // Wrap in a .NET-friendly Stream and call provided code to fill it
                        using (var stream = new IStreamWrapper(iStream))
                        {
                            streamData(stream);
                        }
                    }
                    // Return an IntPtr for the IStream
                    ptr = Marshal.GetComInterfaceForObject(iStream, typeof(IStream));
                    Marshal.ReleaseComObject(iStream);
                    return new Tuple<IntPtr, int>(ptr, NativeMethods.S_OK);
                },
            });
    }

matthieu 建议改成；

public void SetData(short dataFormat, int index, Stream stream)
{
  ...
  var iStream = new StreamWrapper(stream);
  ...
  // Ensure the following line is commented out:
  //Marshal.ReleaseComObject(iStream);
  return new Tuple<IntPtr, int>(ptr, NativeMethods.S_OK);
 ...
}

在我进行这些更改后，以下调用将不起作用； (这就是我需要帮助的地方)我该如何解决这个电话问题；

            foreach (var fileDescriptor in fileDescriptors)
        {
            **SetData(FILECONTENTS, index, fileDescriptor.StreamContents);**
            index++;
        }

基本上将“Action streamData”更改为“Stream stream”导致了我的问题。我不确定在进行更改后如何调用它。

所有这些代码都来自 Delays VirtualFileDataObject。我不知道我是否应该把它贴在这里。但是，如果您点击上面的链接，它会将您带到该博客，以便您查看。

我太接近了，只是想不出这最后一步，谢谢你看一看

Answer 1

我遇到了完全相同的问题。这是我为解决此问题所做的工作(正如您所说，其他答案中尚未完全解决)

1) 修改 FileDescriptor 的 StreamContents 属性:

public Action<Stream> StreamContents { get; set; }

为此:

public Func<Stream> StreamContents { get; set; }

(而不是传递客户端可以写入的 Stream，我们期望一个我们可以从中读取的 Stream，这正是 Explorer 的工作方式和它所期望的)

2) 从这里修改 SetData 方法重载:

public void SetData(short dataFormat, int index, Action<Stream> streamData)

为此:

public void SetData(short dataFormat, int index, Func<Stream> streamData)

3) 将 SetData 代码的 GetData lambda 更改为:

GetData = () =>
{
    ManagedIStream istream = null;
    if (streamData != null)
    {
        Stream stream = streamData();
        if (stream != null)
        {
            istream = new ManagedIStream(stream);
        }
    }

    IntPtr ptr = istream != null ? Marshal.GetComInterfaceForObject(istream, typeof(IStream)) : IntPtr.Zero;
    return new Tuple<IntPtr, int>(ptr, NativeMethods.S_OK);
},

4)在代码中加入这个ManagedIStream类(也可以完全删除IStreamWrapper类)

private class ManagedIStream : IStream
{
    private Stream _stream;

    public ManagedIStream(Stream stream)
    {
        _stream = stream;
    }

    public void Clone(out IStream ppstm)
    {
        throw new NotImplementedException();
    }

    public void Commit(int grfCommitFlags)
    {
        throw new NotImplementedException();
    }

    public void CopyTo(IStream pstm, long cb, IntPtr pcbRead, IntPtr pcbWritten)
    {
        throw new NotImplementedException();
    }

    public void LockRegion(long libOffset, long cb, int dwLockType)
    {
        throw new NotImplementedException();
    }

    public void Read(byte[] pv, int cb, IntPtr pcbRead)
    {
        int read = _stream.Read(pv, 0, cb);
        if (pcbRead != IntPtr.Zero)
        {
            Marshal.WriteInt32(pcbRead, read);
        }
    }

    public void Revert()
    {
        throw new NotImplementedException();
    }

    public void Seek(long dlibMove, int dwOrigin, IntPtr plibNewPosition)
    {
        long newPos = _stream.Seek(dlibMove, (SeekOrigin)dwOrigin);
        if (plibNewPosition != IntPtr.Zero)
        {
            Marshal.WriteInt64(plibNewPosition, newPos);
        }
    }

    public void SetSize(long libNewSize)
    {
        _stream.SetLength(libNewSize);
    }

    public void Stat(out System.Runtime.InteropServices.ComTypes.STATSTG pstatstg, int grfStatFlag)
    {
        const int STGTY_STREAM = 2;
        pstatstg = new System.Runtime.InteropServices.ComTypes.STATSTG();
        pstatstg.type = STGTY_STREAM;
        pstatstg.cbSize = _stream.Length;
        pstatstg.grfMode = 0;

        if (_stream.CanRead && _stream.CanWrite)
        {
            const int STGM_READWRITE = 0x00000002;
            pstatstg.grfMode |= STGM_READWRITE;
            return;
        }

        if (_stream.CanRead)
        {
            const int STGM_READ = 0x00000000;
            pstatstg.grfMode |= STGM_READ;
            return;
        }

        if (_stream.CanWrite)
        {
            const int STGM_WRITE = 0x00000001;
            pstatstg.grfMode |= STGM_WRITE;
            return;
        }

        throw new IOException();
    }

    public void UnlockRegion(long libOffset, long cb, int dwLockType)
    {
        throw new NotImplementedException();
    }

    public void Write(byte[] pv, int cb, IntPtr pcbWritten)
    {
        _stream.Write(pv, 0, cb);
        if (pcbWritten != IntPtr.Zero)
        {
            Marshal.WriteInt32(pcbWritten, cb);
        }
    }
}

就是这样。现在您可以像这样使用代码(使用与此处提供的原始文章中相同的示例:http://dlaa.me/blog/post/9913083):

new VirtualFileDataObject.FileDescriptor
{
    Name = "Alphabet.txt",
    Length = 26,
    ChangeTimeUtc = DateTime.Now.AddDays(-1),
    StreamContents = () =>
    {
        var contents = Enumerable.Range('a', 26).Select(i => (byte)i).ToArray();
        MemoryStream ms = new MemoryStream(contents); // don't dispose/using here, it would be too early
        return ms;
    }
};