C# - FolderBrowserDialog im Vista Style

/// <summary>
/// Stellt einen Auswahldialog für Ordner und Systemelemente ab Windows Vista bereit.
/// </summary>
public sealed class VistaFolderBrowserDialog
{
    #region Properties

    /// <summary>
    /// Ruft den ausgewählten Ordnerpfad ab bzw. legt diesen fest.
    /// </summary>
    public string SelectedPath { get; set; }
    /// <summary>
    /// Ruft den Anzeigenamen eines einzelnen, ausgewählten Elements ab.
    /// </summary>
    public string SelectedElementName { get; private set; }
    /// <summary>
    /// Ruft ein Array mit Ordnerpfaden der ausgewählten Ordner ab.
    /// </summary>
    public string[] SelectedPaths { get; private set; }
    /// <summary>
    /// Ruft ein Array mit den Namen der ausgewählten Elemente ab.
    /// </summary>
    public string[] SelectedElementNames { get; private set; }

    /// <summary>
    /// Ruft einen Wert ab der angibt ob auch Elemente ausgewählt werden können, die keine Ordner sind oder legt diesen fest.
    /// </summary>
    public bool AllowNonStoragePlaces { get; set; }
    /// <summary>
    /// Ruft einen Wert ab der angibt ob mehrere Elemente ausgewählt werden können oder legt diesen fest.
    /// </summary>
    public bool Multiselect { get; set; }

    #endregion

    #region Public Methods

    /// <summary>
    /// Zeigt den Auswahldialog an.
    /// </summary>
    /// <returns><c>true</c> wenn der Benutzer die Ordnerauswahl bestätigte; andernfalls <c>false</c></returns>
    public bool ShowDialog() => ShowDialog(IntPtr.Zero);

    /// <summary>
    /// Zeigt den Auswahldialog an.
    /// </summary>
    /// <param name="owner">Der Besitzer des Fensters</param>
    /// <returns><c>true</c> wenn der Benutzer die Ordnerauswahl bestätigte; andernfalls <c>false</c></returns>
    public bool ShowDialog(Window owner) => ShowDialog(owner == null ? IntPtr.Zero : new WindowInteropHelper(owner).Handle);

    /// <summary>
    /// Zeigt den Auswahldialog an.
    /// </summary>
    /// <param name="owner">Der Besitzer des Fensters</param>
    /// <returns><c>true</c> wenn der Benutzer die Ordnerauswahl bestätigte; andernfalls <c>false</c></returns>
    public bool ShowDialog(IWin32Window owner) => ShowDialog(owner == null ? IntPtr.Zero : owner.Handle);

    /// <summary>
    /// Zeigt den Auswahldialog an.
    /// </summary>
    /// <param name="owner">Der Besitzer des Fensters</param>
    /// <returns><c>true</c> wenn der Benutzer die Ordnerauswahl bestätigte; andernfalls <c>false</c></returns>
    public bool ShowDialog(IntPtr owner)
    {
        if (Environment.OSVersion.Version.Major < 6)
        {
            throw new InvalidOperationException("The dialog need at least Windows Vista to work.");
        }

        var dialog = CreateNativeDialog();
        try
        {
            SetInitialFolder(dialog);
            SetOptions(dialog);

            if (dialog.Show(owner) != 0)
            {
                return false;
            }

            SetDialogResults(dialog);

            return true;
        }
        finally
        {
            Marshal.ReleaseComObject(dialog);
        }
    }

    #endregion

    #region Helper

    void GetPathAndElementName(IShellItem item, out string path, out string elementName)
    {
        item.GetDisplayName(SIGDN.PARENTRELATIVEFORADDRESSBAR, out elementName);
        try
        {
            item.GetDisplayName(SIGDN.FILESYSPATH, out path);
        }
        catch (ArgumentException ex) when (ex.HResult == -2147024809)
        {
            path = null;
        }
    }

    IFileOpenDialog CreateNativeDialog()
    {
        return new FileOpenDialog() as IFileOpenDialog;
    }
    void SetInitialFolder(IFileOpenDialog dialog)
    {
        IShellItem item;
        if (!string.IsNullOrEmpty(this.SelectedPath))
        {
            IntPtr idl;
            uint atts = 0;
            if (NativeMethods.SHILCreateFromPath(this.SelectedPath, out idl, ref atts) == 0
                && NativeMethods.SHCreateShellItem(IntPtr.Zero, IntPtr.Zero, idl, out item) == 0)
            {
                dialog.SetFolder(item);
            }
        }
    }
    void SetOptions(IFileOpenDialog dialog)
    {
        dialog.SetOptions(GetDialogOptions());
    }
    FOS GetDialogOptions()
    {
        var options = FOS.PICKFOLDERS;
        if (this.Multiselect)
        {
            options |= FOS.ALLOWMULTISELECT;
        }
        if (!AllowNonStoragePlaces)
        {
            options |= FOS.FORCEFILESYSTEM;
        }
        return options;
    }
    void SetDialogResults(IFileOpenDialog dialog)
    {
        IShellItem item;
        if (!this.Multiselect)
        {
            dialog.GetResult(out item);
            string path, value;
            GetPathAndElementName(item, out path, out value);
            this.SelectedPath = path;
            this.SelectedPaths = new[] { path };
            this.SelectedElementName = value;
            this.SelectedElementNames = new[] { value };
        }
        else
        {
            IShellItemArray items;
            dialog.GetResults(out items);

            uint count;
            items.GetCount(out count);

            this.SelectedPaths = new string[count];
            this.SelectedElementNames = new string[count];

            for (uint i = 0; i < count; ++i)
            {
                items.GetItemAt(i, out item);
                string path, value;
                GetPathAndElementName(item, out path, out value);
                this.SelectedPaths[i] = path;
                this.SelectedElementNames[i] = value;
            }

            this.SelectedPath = null;
            this.SelectedElementName = null;
        }
    }

    #endregion

    #region Types

    class NativeMethods
    {
        [DllImport("shell32.dll")]
        public static extern int SHILCreateFromPath([MarshalAs(UnmanagedType.LPWStr)] string pszPath, out IntPtr ppIdl, ref uint rgflnOut);

        [DllImport("shell32.dll")]
        public static extern int SHCreateShellItem(IntPtr pidlParent, IntPtr psfParent, IntPtr pidl, out IShellItem ppsi);

        [DllImport("user32.dll")]
        public static extern IntPtr GetActiveWindow();

    }

    [ComImport, Guid("43826D1E-E718-42EE-BC55-A1E261C37BFE"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
    interface IShellItem
    {
        void BindToHandler([In, MarshalAs(UnmanagedType.Interface)] IntPtr pbc, [In] ref Guid bhid, [In] ref Guid riid, out IntPtr ppv);
        void GetParent([MarshalAs(UnmanagedType.Interface)] out IShellItem ppsi);
        void GetDisplayName([In] SIGDN sigdnName, [MarshalAs(UnmanagedType.LPWStr)] out string ppszName);
        void GetAttributes([In] uint sfgaoMask, out uint psfgaoAttribs);
        void Compare([In, MarshalAs(UnmanagedType.Interface)] IShellItem psi, [In] uint hint, out int piOrder);
    }

    [ComImport, Guid("B63EA76D-1F85-456F-A19C-48159EFA858B"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
    interface IShellItemArray
    {
        void BindToHandler([In, MarshalAs(UnmanagedType.Interface)] IntPtr pbc, [In] ref Guid rbhid, [In] ref Guid riid, out IntPtr ppvOut);
        void GetPropertyStore([In] int Flags, [In] ref Guid riid, out IntPtr ppv);
        void GetPropertyDescriptionList([In, MarshalAs(UnmanagedType.Struct)] ref IntPtr keyType, [In] ref Guid riid, out IntPtr ppv);
        void GetAttributes([In, MarshalAs(UnmanagedType.I4)] IntPtr dwAttribFlags, [In] uint sfgaoMask, out uint psfgaoAttribs);
        void GetCount(out uint pdwNumItems);
        void GetItemAt([In] uint dwIndex, [MarshalAs(UnmanagedType.Interface)] out IShellItem ppsi);
        void EnumItems([MarshalAs(UnmanagedType.Interface)] out IntPtr ppenumShellItems);
    }

    [ComImport, Guid("d57c7288-d4ad-4768-be02-9d969532d960"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown), CoClass(typeof(FileOpenDialog))]
    interface IFileOpenDialog //: IFileDialog
    {
        [PreserveSig]
        int Show([In] IntPtr parent);
        void SetFileTypes([In] uint cFileTypes, [In, MarshalAs(UnmanagedType.Struct)] ref IntPtr rgFilterSpec);
        void SetFileTypeIndex([In] uint iFileType);
        void GetFileTypeIndex(out uint piFileType);
        void Advise([In, MarshalAs(UnmanagedType.Interface)] IntPtr pfde, out uint pdwCookie);
        void Unadvise([In] uint dwCookie);
        void SetOptions([In] FOS fos);
        void GetOptions(out FOS pfos);
        void SetDefaultFolder([In, MarshalAs(UnmanagedType.Interface)] IShellItem psi);
        void SetFolder([In, MarshalAs(UnmanagedType.Interface)] IShellItem psi);
        void GetFolder([MarshalAs(UnmanagedType.Interface)] out IShellItem ppsi);
        void GetCurrentSelection([MarshalAs(UnmanagedType.Interface)] out IShellItem ppsi);
        void SetFileName([In, MarshalAs(UnmanagedType.LPWStr)] string pszName);
        void GetFileName([MarshalAs(UnmanagedType.LPWStr)] out string pszName);
        void SetTitle([In, MarshalAs(UnmanagedType.LPWStr)] string pszTitle);
        void SetOkButtonLabel([In, MarshalAs(UnmanagedType.LPWStr)] string pszText);
        void SetFileNameLabel([In, MarshalAs(UnmanagedType.LPWStr)] string pszLabel);
        void GetResult([MarshalAs(UnmanagedType.Interface)] out IShellItem ppsi);
        void AddPlace([In, MarshalAs(UnmanagedType.Interface)] IShellItem psi, FileDialogCustomPlace fdcp);
        void SetDefaultExtension([In, MarshalAs(UnmanagedType.LPWStr)] string pszDefaultExtension);
        void Close([MarshalAs(UnmanagedType.Error)] int hr);
        void SetClientGuid([In] ref Guid guid);
        void ClearClientData();
        void SetFilter([MarshalAs(UnmanagedType.Interface)] IntPtr pFilter);
        void GetResults([MarshalAs(UnmanagedType.Interface)] out IShellItemArray ppenum);
        void GetSelectedItems([MarshalAs(UnmanagedType.Interface)] out IShellItemArray ppsai);
    }

    [ComImport, Guid("DC1C5A9C-E88A-4dde-A5A1-60F82A20AEF7")]
    class FileOpenDialog { }

    enum SIGDN : uint
    {
        DESKTOPABSOLUTEEDITING = 0x8004c000,
        DESKTOPABSOLUTEPARSING = 0x80028000,
        FILESYSPATH = 0x80058000,
        NORMALDISPLAY = 0,
        PARENTRELATIVE = 0x80080001,
        PARENTRELATIVEEDITING = 0x80031001,
        PARENTRELATIVEFORADDRESSBAR = 0x8007c001,
        PARENTRELATIVEPARSING = 0x80018001,
        URL = 0x80068000
    }

    [Flags]
    enum FOS
    {
        ALLNONSTORAGEITEMS = 0x80,
        ALLOWMULTISELECT = 0x200,
        CREATEPROMPT = 0x2000,
        DEFAULTNOMINIMODE = 0x20000000,
        DONTADDTORECENT = 0x2000000,
        FILEMUSTEXIST = 0x1000,
        FORCEFILESYSTEM = 0x40,
        FORCESHOWHIDDEN = 0x10000000,
        HIDEMRUPLACES = 0x20000,
        HIDEPINNEDPLACES = 0x40000,
        NOCHANGEDIR = 8,
        NODEREFERENCELINKS = 0x100000,
        NOREADONLYRETURN = 0x8000,
        NOTESTFILECREATE = 0x10000,
        NOVALIDATE = 0x100,
        OVERWRITEPROMPT = 2,
        PATHMUSTEXIST = 0x800,
        PICKFOLDERS = 0x20,
        SHAREAWARE = 0x4000,
        STRICTFILETYPES = 4
    }

    #endregion
}