Microsoft.VisualStudio.Project.DragDropHelper.GetDroppedFiles C# (CSharp) Method

        public static ReadOnlyCollection<string> GetDroppedFiles(ushort format, Microsoft.VisualStudio.OLE.Interop.IDataObject dataObject, out DropDataType ddt)
        {
            ddt = DropDataType.None;
            List<string> droppedFiles = new List<string>();

            // try HDROP
            FORMATETC fmtetc = CreateFormatEtc(format);

            if(QueryGetData(dataObject, ref fmtetc) == VSConstants.S_OK)
            {
                STGMEDIUM stgmedium = DragDropHelper.GetData(dataObject, ref fmtetc);
                if(stgmedium.tymed == (uint)TYMED.TYMED_HGLOBAL)
                {
                    // We are releasing the cloned hglobal here.
                    IntPtr dropInfoHandle = stgmedium.unionmember;
                    if(dropInfoHandle != IntPtr.Zero)
                    {
                        ddt = DropDataType.Shell;
                        try
                        {
                            uint numFiles = UnsafeNativeMethods.DragQueryFile(dropInfoHandle, 0xFFFFFFFF, null, 0);

                            // We are a directory based project thus a projref string is placed on the clipboard.
                            // We assign the maximum length of a projref string.
                            // The format of a projref is : <Proj Guid>|<project rel path>|<file path>
                            uint lenght = (uint)Guid.Empty.ToString().Length + 2 * NativeMethods.MAX_PATH + 2;
                            char[] moniker = new char[lenght + 1];
                            for(uint fileIndex = 0; fileIndex < numFiles; fileIndex++)
                            {
                                uint queryFileLength = UnsafeNativeMethods.DragQueryFile(dropInfoHandle, fileIndex, moniker, lenght);
                                string filename = new String(moniker, 0, (int)queryFileLength);
                                droppedFiles.Add(filename);
                            }
                        }
                        finally
                        {
                            Marshal.FreeHGlobal(dropInfoHandle);
                        }
                    }
                }
            }

            return droppedFiles.AsReadOnly();
        }

        /// <summary>
        /// Process dataobject from Drag/Drop/Cut/Copy/Paste operation
        /// </summary>
        /// <remarks>The targetNode is set if the method is called from a drop operation, otherwise it is null</remarks>
        internal DropDataType ProcessSelectionDataObject(IOleDataObject dataObject, HierarchyNode targetNode)
        {
            DropDataType dropDataType    = DropDataType.None;
            bool         isWindowsFormat = false;

            // Try to get it as a directory based project.
            List <string> filesDropped = DragDropHelper.GetDroppedFiles(DragDropHelper.CF_VSSTGPROJECTITEMS, dataObject, out dropDataType);

            if (filesDropped.Count == 0)
            {
                filesDropped = DragDropHelper.GetDroppedFiles(DragDropHelper.CF_VSREFPROJECTITEMS, dataObject, out dropDataType);
            }
            if (filesDropped.Count == 0)
            {
                filesDropped    = DragDropHelper.GetDroppedFiles(NativeMethods.CF_HDROP, dataObject, out dropDataType);
                isWindowsFormat = (filesDropped.Count > 0);
            }

            if (dropDataType != DropDataType.None && filesDropped.Count > 0)
            {
                string[] filesDroppedAsArray = filesDropped.ToArray();

                HierarchyNode node = (targetNode == null) ? this : targetNode;

                // For directory based projects the content of the clipboard is a double-NULL terminated list of Projref strings.
                if (isWindowsFormat)
                {
                    // This is the code path when source is windows explorer
                    VSADDRESULT[] vsaddresults = new VSADDRESULT[1];
                    vsaddresults[0] = VSADDRESULT.ADDRESULT_Failure;
                    int addResult = AddItem(node.ID, VSADDITEMOPERATION.VSADDITEMOP_OPENFILE, null, (uint)filesDropped.Count, filesDroppedAsArray, IntPtr.Zero, vsaddresults);
                    if (addResult != VSConstants.S_OK && addResult != VSConstants.S_FALSE && addResult != (int)OleConstants.OLECMDERR_E_CANCELED &&
                        vsaddresults[0] != VSADDRESULT.ADDRESULT_Success)
                    {
                        ErrorHandler.ThrowOnFailure(addResult);
                    }

                    return(dropDataType);
                }
                else
                {
                    if (AddFilesFromProjectReferences(node, filesDroppedAsArray))
                    {
                        return(dropDataType);
                    }
                }
            }

            // If we reached this point then the drop data must be set to None.
            // Otherwise the OnPaste will be called with a valid DropData and that would actually delete the item.
            return(DropDataType.None);
        }