C# 文件对话框选择文件夹

using System;
using System.IO;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Windows.Forms;

internal class OpenFolderDialog : IDisposable {

    /// <summary>
    /// Gets/sets folder in which dialog will be open.
    /// </summary>
    public string InitialFolder { get; set; }

    /// <summary>
    /// Gets/sets directory in which dialog will be open if there is no recent directory available.
    /// </summary>
    public string DefaultFolder { get; set; }

    /// <summary>
    /// Gets selected folder.
    /// </summary>
    public string Folder { get; private set; }


    internal DialogResult ShowDialog(IWin32Window owner) {
        if (Environment.OSVersion.Version.Major >= 6) {
            return ShowVistaDialog(owner);
        } else {
            return ShowLegacyDialog(owner);
        }
    }

    private DialogResult ShowVistaDialog(IWin32Window owner) {
        var frm = (NativeMethods.IFileDialog)(new NativeMethods.FileOpenDialogRCW());
        uint options;
        frm.GetOptions(out options);
        options |= NativeMethods.FOS_PICKFOLDERS | NativeMethods.FOS_FORCEFILESYSTEM | NativeMethods.FOS_NOVALIDATE | NativeMethods.FOS_NOTESTFILECREATE | NativeMethods.FOS_DONTADDTORECENT;
        frm.SetOptions(options);
        if (this.InitialFolder != null) {
            NativeMethods.IShellItem directoryShellItem;
            var riid = new Guid("43826D1E-E718-42EE-BC55-A1E261C37BFE"); //IShellItem
            if (NativeMethods.SHCreateItemFromParsingName(this.InitialFolder, IntPtr.Zero, ref riid, out directoryShellItem) == NativeMethods.S_OK) {
                frm.SetFolder(directoryShellItem);
            }
        }
        if (this.DefaultFolder != null) {
            NativeMethods.IShellItem directoryShellItem;
            var riid = new Guid("43826D1E-E718-42EE-BC55-A1E261C37BFE"); //IShellItem
            if (NativeMethods.SHCreateItemFromParsingName(this.DefaultFolder, IntPtr.Zero, ref riid, out directoryShellItem) == NativeMethods.S_OK) {
                frm.SetDefaultFolder(directoryShellItem);
            }
        }

        if (frm.Show(owner.Handle) == NativeMethods.S_OK) {
            NativeMethods.IShellItem shellItem;
            if (frm.GetResult(out shellItem) == NativeMethods.S_OK) {
                IntPtr pszString;
                if (shellItem.GetDisplayName(NativeMethods.SIGDN_FILESYSPATH, out pszString) == NativeMethods.S_OK) {
                    if (pszString != IntPtr.Zero) {
                        try {
                            this.Folder = Marshal.PtrToStringAuto(pszString);
                            return DialogResult.OK;
                        } finally {
                            Marshal.FreeCoTaskMem(pszString);
                        }
                    }
                }
            }
        }
        return DialogResult.Cancel;
    }

    private DialogResult ShowLegacyDialog(IWin32Window owner) {
        using (var frm = new SaveFileDialog()) {
            frm.CheckFileExists = false;
            frm.CheckPathExists = true;
            frm.CreatePrompt = false;
            frm.Filter = "|" + Guid.Empty.ToString();
            frm.FileName = "any";
            if (this.InitialFolder != null) { frm.InitialDirectory = this.InitialFolder; }
            frm.OverwritePrompt = false;
            frm.Title = "Select Folder";
            frm.ValidateNames = false;
            if (frm.ShowDialog(owner) == DialogResult.OK) {
                this.Folder = Path.GetDirectoryName(frm.FileName);
                return DialogResult.OK;
            } else {
                return DialogResult.Cancel;
            }
        }
    }


    public void Dispose() { } //just to have possibility of Using statement.

}

internal static class NativeMethods {

    #region Constants

    public const uint FOS_PICKFOLDERS = 0x00000020;
    public const uint FOS_FORCEFILESYSTEM = 0x00000040;
    public const uint FOS_NOVALIDATE = 0x00000100;
    public const uint FOS_NOTESTFILECREATE = 0x00010000;
    public const uint FOS_DONTADDTORECENT = 0x02000000;

    public const uint S_OK = 0x0000;

    public const uint SIGDN_FILESYSPATH = 0x80058000;

    #endregion


    #region COM

    [ComImport, ClassInterface(ClassInterfaceType.None), TypeLibType(TypeLibTypeFlags.FCanCreate), Guid("DC1C5A9C-E88A-4DDE-A5A1-60F82A20AEF7")]
    internal class FileOpenDialogRCW { }


    [ComImport(), Guid("42F85136-DB7E-439C-85F1-E4075D135FC8"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
    internal interface IFileDialog {
        [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
        [PreserveSig()]
        uint Show([In, Optional] IntPtr hwndOwner); //IModalWindow 


        [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
        uint SetFileTypes([In] uint cFileTypes, [In, MarshalAs(UnmanagedType.LPArray)] IntPtr rgFilterSpec);

        [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
        uint SetFileTypeIndex([In] uint iFileType);

        [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
        uint GetFileTypeIndex(out uint piFileType);

        [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
        uint Advise([In, MarshalAs(UnmanagedType.Interface)] IntPtr pfde, out uint pdwCookie);

        [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
        uint Unadvise([In] uint dwCookie);

        [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
        uint SetOptions([In] uint fos);

        [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
        uint GetOptions(out uint fos);

        [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
        void SetDefaultFolder([In, MarshalAs(UnmanagedType.Interface)] IShellItem psi);

        [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
        uint SetFolder([In, MarshalAs(UnmanagedType.Interface)] IShellItem psi);

        [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
        uint GetFolder([MarshalAs(UnmanagedType.Interface)] out IShellItem ppsi);

        [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
        uint GetCurrentSelection([MarshalAs(UnmanagedType.Interface)] out IShellItem ppsi);

        [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
        uint SetFileName([In, MarshalAs(UnmanagedType.LPWStr)] string pszName);

        [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
        uint GetFileName([MarshalAs(UnmanagedType.LPWStr)] out string pszName);

        [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
        uint SetTitle([In, MarshalAs(UnmanagedType.LPWStr)] string pszTitle);

        [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
        uint SetOkButtonLabel([In, MarshalAs(UnmanagedType.LPWStr)] string pszText);

        [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
        uint SetFileNameLabel([In, MarshalAs(UnmanagedType.LPWStr)] string pszLabel);

        [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
        uint GetResult([MarshalAs(UnmanagedType.Interface)] out IShellItem ppsi);

        [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
        uint AddPlace([In, MarshalAs(UnmanagedType.Interface)] IShellItem psi, uint fdap);

        [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
        uint SetDefaultExtension([In, MarshalAs(UnmanagedType.LPWStr)] string pszDefaultExtension);

        [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
        uint Close([MarshalAs(UnmanagedType.Error)] uint hr);

        [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
        uint SetClientGuid([In] ref Guid guid);

        [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
        uint ClearClientData();

        [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
        uint SetFilter([MarshalAs(UnmanagedType.Interface)] IntPtr pFilter);
    }


    [ComImport, Guid("43826D1E-E718-42EE-BC55-A1E261C37BFE"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
    internal interface IShellItem {
        [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
        uint BindToHandler([In] IntPtr pbc, [In] ref Guid rbhid, [In] ref Guid riid, [Out, MarshalAs(UnmanagedType.Interface)] out IntPtr ppvOut);

        [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
        uint GetParent([MarshalAs(UnmanagedType.Interface)] out IShellItem ppsi);

        [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
        uint GetDisplayName([In] uint sigdnName, out IntPtr ppszName);

        [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
        uint GetAttributes([In] uint sfgaoMask, out uint psfgaoAttribs);

        [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
        uint Compare([In, MarshalAs(UnmanagedType.Interface)] IShellItem psi, [In] uint hint, out int piOrder);
    }

    #endregion


    [DllImport("shell32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
    internal static extern int SHCreateItemFromParsingName([MarshalAs(UnmanagedType.LPWStr)] string pszPath, IntPtr pbc, ref Guid riid, [MarshalAs(UnmanagedType.Interface)] out IShellItem ppv);

}