我想启用从基于 Windows 窗体的应用程序到 Windows 资源管理器的拖放功能。大问题：文件存储在数据库中，所以我需要使用延迟数据渲染。有一个article on codeproject.com，但作者使用的是 H_GLOBAL 对象，这会导致文件大于 aprox 的内存问题。 20 MB。我还没有找到使用 IStream 对象的可行解决方案。我认为这一定是可以实现的，因为这不是一个不寻常的情况。 （例如，FTP 程序也需要这样的功能）
编辑：是否可以在用户删除文件时获取事件？所以我可以例如将它复制到 temp 并且资源管理器从那里获取它？也许我的问题有另一种方法......
【问题讨论】：
标签： c# drag-and-drop
AFAIK，没有关于.net 的工作文章。所以你应该自己写，这有点复杂，因为.net DataObject 类是有限的。我有相反任务的工作示例（接受来自资源管理器的延迟渲染文件），但它更容易，因为我不需要自己的 IDataObject 实现。
所以你的任务是：
这是一个起点，并且通常提供足够的信息来实现此类功能。有一点耐心和几次不成功的尝试，你会做到的:)
更新：以下代码缺少很多必要的方法和函数，但主要逻辑在此。
// ...
private static IEnumerable<IVirtualItem> GetDataObjectContent(System.Windows.Forms.IDataObject dataObject)
{
if (dataObject == null)
return null;
List<IVirtualItem> Result = new List<IVirtualItem>();
bool WideDescriptor = dataObject.GetDataPresent(ShlObj.CFSTR_FILEDESCRIPTORW);
bool AnsiDescriptor = dataObject.GetDataPresent(ShlObj.CFSTR_FILEDESCRIPTORA);
if (WideDescriptor || AnsiDescriptor)
{
IDataObject NativeDataObject = dataObject as IDataObject;
if (NativeDataObject != null)
{
object Data = null;
if (WideDescriptor)
Data = dataObject.GetData(ShlObj.CFSTR_FILEDESCRIPTORW);
else
if (AnsiDescriptor)
Data = dataObject.GetData(ShlObj.CFSTR_FILEDESCRIPTORA);
Stream DataStream = Data as Stream;
if (DataStream != null)
{
Dictionary<string, VirtualClipboardFolder> FolderMap =
new Dictionary<string, VirtualClipboardFolder>(StringComparer.OrdinalIgnoreCase);
BinaryReader Reader = new BinaryReader(DataStream);
int Count = Reader.ReadInt32();
for (int I = 0; I < Count; I++)
{
VirtualClipboardItem ClipboardItem;
if (WideDescriptor)
{
FILEDESCRIPTORW Descriptor = ByteArrayHelper.ReadStructureFromStream<FILEDESCRIPTORW>(DataStream);
if (((Descriptor.dwFlags & FD.FD_ATTRIBUTES) > 0) && ((Descriptor.dwFileAttributes & FileAttributes.Directory) > 0))
ClipboardItem = new VirtualClipboardFolder(Descriptor);
else
ClipboardItem = new VirtualClipboardFile(Descriptor, NativeDataObject, I);
}
else
{
FILEDESCRIPTORA Descriptor = ByteArrayHelper.ReadStructureFromStream<FILEDESCRIPTORA>(DataStream);
if (((Descriptor.dwFlags & FD.FD_ATTRIBUTES) > 0) && ((Descriptor.dwFileAttributes & FileAttributes.Directory) > 0))
ClipboardItem = new VirtualClipboardFolder(Descriptor);
else
ClipboardItem = new VirtualClipboardFile(Descriptor, NativeDataObject, I);
}
string ParentFolder = Path.GetDirectoryName(ClipboardItem.FullName);
if (string.IsNullOrEmpty(ParentFolder))
Result.Add(ClipboardItem);
else
{
VirtualClipboardFolder Parent = FolderMap[ParentFolder];
ClipboardItem.Parent = Parent;
Parent.Content.Add(ClipboardItem);
}
VirtualClipboardFolder ClipboardFolder = ClipboardItem as VirtualClipboardFolder;
if (ClipboardFolder != null)
FolderMap.Add(PathHelper.ExcludeTrailingDirectorySeparator(ClipboardItem.FullName), ClipboardFolder);
}
}
}
}
return Result.Count > 0 ? Result : null;
}
// ...
public VirtualClipboardFile : VirtualClipboardItem, IVirtualFile
{
// ...
public Stream Open(FileMode mode, FileAccess access, FileShare share, FileOptions options, long startOffset)
{
if ((mode != FileMode.Open) || (access != FileAccess.Read))
throw new ArgumentException("Only open file mode and read file access supported.");
System.Windows.Forms.DataFormats.Format Format = System.Windows.Forms.DataFormats.GetFormat(ShlObj.CFSTR_FILECONTENTS);
if (Format == null)
return null;
FORMATETC FormatEtc = new FORMATETC();
FormatEtc.cfFormat = (short)Format.Id;
FormatEtc.dwAspect = DVASPECT.DVASPECT_CONTENT;
FormatEtc.lindex = FIndex;
FormatEtc.tymed = TYMED.TYMED_ISTREAM | TYMED.TYMED_HGLOBAL;
STGMEDIUM Medium;
FDataObject.GetData(ref FormatEtc, out Medium);
try
{
switch (Medium.tymed)
{
case TYMED.TYMED_ISTREAM:
IStream MediumStream = (IStream)Marshal.GetTypedObjectForIUnknown(Medium.unionmember, typeof(IStream));
ComStreamWrapper StreamWrapper = new ComStreamWrapper(MediumStream, FileAccess.Read, ComRelease.None);
// Seek from beginning
if (startOffset > 0)
if (StreamWrapper.CanSeek)
StreamWrapper.Seek(startOffset, SeekOrigin.Begin);
else
{
byte[] Null = new byte[256];
int Readed = 1;
while ((startOffset > 0) && (Readed > 0))
{
Readed = StreamWrapper.Read(Null, 0, (int)Math.Min(Null.Length, startOffset));
startOffset -= Readed;
}
}
StreamWrapper.Closed += delegate(object sender, EventArgs e)
{
ActiveX.ReleaseStgMedium(ref Medium);
Marshal.FinalReleaseComObject(MediumStream);
};
return StreamWrapper;
case TYMED.TYMED_HGLOBAL:
byte[] FileContent;
IntPtr MediumLock = Windows.GlobalLock(Medium.unionmember);
try
{
long Size = FSize.HasValue ? FSize.Value : Windows.GlobalSize(MediumLock).ToInt64();
FileContent = new byte[Size];
Marshal.Copy(MediumLock, FileContent, 0, (int)Size);
}
finally
{
Windows.GlobalUnlock(Medium.unionmember);
}
ActiveX.ReleaseStgMedium(ref Medium);
Stream ContentStream = new MemoryStream(FileContent, false);
ContentStream.Seek(startOffset, SeekOrigin.Begin);
return ContentStream;
default:
throw new ApplicationException(string.Format("Unsupported STGMEDIUM.tymed ({0})", Medium.tymed));
}
}
catch
{
ActiveX.ReleaseStgMedium(ref Medium);
throw;
}
}
// ...
【讨论】：
Google 员工可能会觉得这很有用：download a file using windows IStream
【讨论】：