使用VirtualFileDataObject拖放IStream的大型虚拟文件

本文关键字：大型 虚拟 文件 IStream VirtualFileDataObject 拖放 使用 | 更新日期: 2023-09-27 17:54:44

我成功地使用了来自延迟博客的VirtualFileDataObject代码，但我想避免将整个文件流式传输到内存中。

我发现这个以前回答过的关于堆栈溢出的问题拖放大型虚拟文件从c#到Windows资源管理器这个问题是由matthieu回答的，通过改变SetData方法的签名。

这是我的问题，在改变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);
 ...
}

在我做了这些改变之后，下面的调用将不工作;(这就是我需要帮助的地方)

如何修复这个调用?
            foreach (var fileDescriptor in fileDescriptors)
        {
            **SetData(FILECONTENTS, index, fileDescriptor.StreamContents);**
            index++;
        }

基本上改变"Action streamData"到"Stream Stream"是导致我的问题。我不确定如何调用它后的变化。

所有这些代码都来自延迟VirtualFileDataObject。我不知道我是否应该把它贴在这里。但是如果你点击上面的链接，它会把你带到博客，这样你就可以看到它了。

我已经很接近了，只是不能想出最后一步，谢谢你的关注

使用VirtualFileDataObject拖放IStream的大型虚拟文件

我也遇到过同样的问题。以下是我为解决这个问题所做的(正如你所说的，在另一个答案中没有完全解决)

1)修改FileDescriptor的StreamContents属性:

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

: 

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

(而不是传递客户端可以写入的Stream，我们将期望可以从中读取的Stream，这正是Explorer的工作方式和期望)

2)修改SetData方法重载:

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

: 

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

3)更改SetData代码的GetData lambda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)将ManagedIStream类添加到代码中(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;
    }
};
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