使用Alphavss时发生卷影复制错误

iI正在尝试使用alphavss网站上提供的示例代码。我正在尝试包含类VssBackup.cs，然后在我的程序中使用它。很可能我缺少一个dll引用，但在使用组件时没有得到任何错误。有人知道问题出在哪里吗？

我得到3个错误：

找不到类型或命名空间名称"Snapshot"（是否缺少using指令或程序集引用？）

Snapshot _snap;

找不到类型或命名空间名称"IVssAsync"（是否缺少using指令或程序集引用？

     using (IVssAsync async = _backup.GatherWriterMetadata())
     {.......

找不到类型或命名空间名称"Snapshot"（是否缺少using指令或程序集引用？）

_snap = new Snapshot(_backup);

类**VssBackup.cs站点提供的C#示例代码**

/* Copyright (c) 2008-2012 Peter Palotas
 *  
 *  Permission is hereby granted, free of charge, to any person obtaining a copy
 *  of this software and associated documentation files (the "Software"), to deal
 *  in the Software without restriction, including without limitation the rights
 *  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 *  copies of the Software, and to permit persons to whom the Software is
 *  furnished to do so, subject to the following conditions:
 *  
 *  The above copyright notice and this permission notice shall be included in
 *  all copies or substantial portions of the Software.
 *  
 *  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 *  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 *  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 *  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 *  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 *  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 *  THE SOFTWARE.
 */
#region Copyright Notice
/*
 * AlphaVSS Sample Code
 * Written by Jay Miller
 * 
 * This code is hereby released into the public domain, This applies
 * worldwide.
 */
#endregion
using System;
using System.Diagnostics;
using System.Collections.Generic;
using Alphaleonis.Win32.Vss;
using Alphaleonis.Win32.Filesystem;

namespace VssSample
{
   /// <summary>
   /// This class encapsulates some simple VSS logic.  Its goal is to allow
   /// a user to backup a single file from a shadow copy (presumably because
   /// that file is otherwise unavailable on its home volume).
   /// </summary>
   /// <example>
   /// This code creates a shadow copy and copies a single file from
   /// the new snapshot to a location on the D drive.  Here we're
   /// using the AlphaFS library to make a full-file copy of the file.
   /// <code>
   /// string source_file = @"C:'Windows'system32'config'sam";
   /// string backup_root = @"D:'Backups";
   /// string backup_path = Path.Combine(backup_root,
   ///       Path.GetFilename(source_file));
   ///
   /// // Initialize the shadow copy subsystem.
   /// using (VssBackup vss = new VssBackup())
   /// {
   ///    vss.Setup(Path.GetPathRoot(source_file));
   ///    string snap_path = vss.GetSnapshotPath(source_file);
   /// 
   ///    // Here we use the AlphaFS library to make the copy.
   ///    Alphaleonis.Win32.Filesystem.File.Copy(snap_path, backup_path);
   /// }
   /// </code>
   /// This code creates a shadow copy and opens a stream over a file
   /// on the new snapshot volume.
   /// <code>
   /// string source_file = @"C:'Windows'system32'config'sam";
   /// 
   /// // Initialize the shadow copy subsystem.
   /// using (VssBackup vss = new VssBackup())
   /// {
   ///    vss.Setup(Path.GetPathRoot(filename));
   ///    
   ///    // We can now access the shadow copy by either retrieving a stream:
   ///    using (Stream s = vss.GetStream(filename))
   ///    {
   ///       Debug.Assert(s.CanRead == true);
   ///       Debug.Assert(s.CanWrite == false);
   ///    }
   /// }
   /// </code>
   /// </example>
   public class VssBackup : IDisposable
   {
      /// <summary>
      /// Setting this flag to true will enable 'component mode', which
      /// does not, in this example, do much of any substance.
      /// </summary>
      /// <remarks>
      /// VSS has the ability to selectively disable VSS-compatible
      /// components according to the specifics of the current backup.  One
      /// might, for example, only quiesce Outlook if only the Outlook PST
      /// file is intended to be backed up.  The ExamineComponents() method
      /// provides a framework for this sort of mode if you're interested.
      /// Otherwise, this example code quiesces all VSS-compatible components
      /// before making its shadow copy.
      /// </remarks>
      bool ComponentMode = false;
      /// <summary>A reference to the VSS context.</summary>
      IVssBackupComponents _backup;
      /// <summary>Some persistent context for the current snapshot.</summary>
      Snapshot _snap;
      /// <summary>
      /// Constructs a VssBackup object and initializes some of the necessary
      /// VSS structures.
      /// </summary>
      public VssBackup()
      {
         InitializeBackup();
      }
      /// <summary>
      /// Sets up a shadow copy against the specified volume.
      /// </summary>
      /// <remarks>
      /// This methods is separated out from the constructor because if it
      /// throws, we still want the Dispose() method to be called.
      /// </remarks>
      /// <param name="volumeName">Name of the volume to copy.</param>
      public void Setup(string volumeName)
      {
         Discovery(volumeName);
         PreBackup();
      }
      /// <summary>
      /// The disposal of this object involves sending completion notices
      /// to the writers, removing the shadow copies from the system and
      /// finally releasing the BackupComponents object.  This method must
      /// be called when this class is no longer used.
      /// </summary>
      public void Dispose()
      {
         try { Complete(true); } catch { }
         if (_snap != null)
         {
            _snap.Dispose();
            _snap = null;
         }
         if (_backup != null)
         {
            _backup.Dispose();
            _backup = null;
         }
      }
      /// <summary>
      /// This stage initializes both the requester (this program) and 
      /// any writers on the system in preparation for a backup and sets
      /// up a communcation channel between the two.
      /// </summary>
      void InitializeBackup()
      {
         // Here we are retrieving an OS-dependent object that encapsulates
         // all of the VSS functionality.  The OS indepdence that this single
         // factory method provides is one of AlphaVSS's major strengths!
         IVssImplementation vss = VssUtils.LoadImplementation();
         // Now we create a BackupComponents object to manage the backup.
         // This object will have a one-to-one relationship with its backup
         // and must be cleaned up when the backup finishes (ie. it cannot
         // be reused).
         //
         // Note that this object is a member of our class, as it needs to
         // stick around for the full backup.
         _backup = vss.CreateVssBackupComponents();
         // Now we must initialize the components.  We can either start a
         // fresh backup by passing null here, or we could resume a previous
         // backup operation through an earlier use of the SaveXML method.
         _backup.InitializeForBackup(null);
         // At this point, we're supposed to establish communication with
         // the writers on the system.  It is possible before this step to
         // enable or disable specific writers via the BackupComponents'
         // Enable* and Disable* methods.
         //
         // Note the 'using' construct here to dispose of the asynchronous
         // comm link once we no longer need it.
         using (IVssAsync async = _backup.GatherWriterMetadata())
         {
            // Because allowing writers to prepare their metadata can take
            // a while, we are given a VssAsync object that gives us some
            // status on the background operation.  In this case, we just
            // wait for it to finish.
            async.Wait();
         }
      }
      /// <summary>
      /// This stage involes the requester (us, again) processing the
      /// information it received from writers on the system to find out
      /// which volumes - if any - must be shadow copied to perform a full
      /// backup.
      /// </summary>
      void Discovery(string fullPath)
      {
         if (ComponentMode)
            // In component mode, we would need to enumerate through each
            // component and decide whether it should be added to our
            // backup document.
            ExamineComponents(fullPath);
         else
            // Once we are finished with the writer metadata, we can dispose
            // of it.  If we were in component mode, we would want to keep it
            // around so that we could notify the writers of our success or
            // failure when we finish the backup.
            _backup.FreeWriterMetadata();
         // Now we use our helper class to add the appropriate volume to the
         // shadow copy set.
         _snap = new Snapshot(_backup);
         _snap.AddVolume(Path.GetPathRoot(fullPath));
      }
      /// <summary>
      /// This method is optional in this implementation, and in fact does
      /// nothing of substance.  It does demonstrate how one might parse
      /// through the various writers on the system and add them to the
      /// backup document if necessary.
      /// </summary>
      /// <param name="fullPath">The full path of the file to back up.</param>
      void ExamineComponents(string fullPath)
      {
         // At this point it is the requester's duty to examine what the
         // writers have prepared for us.  The WriterMetadata property
         // (in place of the C API's 'GetWriterMetadata' function) collects
         // metadata from each writer behind a list interface.
         IList<IVssExamineWriterMetadata> writer_mds = _backup.WriterMetadata;
         // If you receive a "bad state" error when enumerating, you might
         // have a registry inconsistency from a program that improperly
         // uninstalled itself.  If your event log is showing an error like,
         // "ContentIndexingService called routine RegQueryValueExW which
         // failed," you'll want to read Microsoft's KB article #907574.
         foreach (IVssExamineWriterMetadata metadata in writer_mds)
         {
            // We can see the name of the writer, if we like.
            Trace.WriteLine("Examining metadata for " + metadata.WriterName);
            // The important bit of the writers' metadata is the list of
            // components each writer is broken into.  These components are
            // responsible for some number of files, so going through this
            // data allows us to construct an initial list of files for our
            // shadow copies.
            foreach (IVssWMComponent cmp in metadata.Components)
            {
               // Print out some info for each component.
               Trace.WriteLine("  Component: " + cmp.ComponentName);
               Trace.WriteLine("  Component info: " + cmp.Caption);
               // If a component is available for backup, it's then up to us to
               // decide whether it is relevant to the current backup.  To do
               // this, we may examine the files each component manages.
               foreach (VssWMFileDescription file in cmp.Files)
               {
                  // The idea here is to find out whether these files are
                  // relevant to whatever purpose your application holds.  If
                  // they are, you should a) add this component to your backup
                  // set so VSS involves it in the shadow copy operation, and
                  // b) record the files' volume names so you know later which
                  // volumes need to be shadow copied.
                  // I'm not worried about that stuff for this example, though,
                  // so instead I'm printing out the stuff you might need to
                  // examine if you have requirements of that sort.
                  Trace.WriteLine("    Path: " + file.Path);
                  Trace.WriteLine("       Spec: " + file.FileSpecification);
                  // Here we might insert some logic to:
                  //
                  //  1. Check whether the AlternateLocation property is valid.
                  //  2. Expand environment vairables in either Path.or
                  //     AlternateLocation, as appropriate.
                  //  3. Considering the FileSpecification and the IsRecursive
                  //     properties, decide whether this component manages
                  //     the file(s) you wish to backup (in this case, the
                  //     fullPath argument).
                  //
                  // If this component is relevant, add it with AddComponent().
                  // (The FileToPathSpecification method below might help with
                  // some of these steps.)
               }
            }
         }
      }
      /// <summary>
      /// This phase of the backup is focused around creating the shadow copy.
      /// We will notify writers of the impending snapshot, after which they
      /// have a short period of time to get their on-disk data in order and
      /// then quiesce writing.
      /// </summary>
      void PreBackup()
      {
         Debug.Assert(_snap != null);
         // This next bit is a way to tell writers just what sort of backup
         // they should be preparing for.  The important parts for us now
         // are the first and third arguments: we want to do a full,
         // backup and, depending on whether we are in component mode, either
         // a full-volume backup or a backup that only requires specific
         // components.
         _backup.SetBackupState(ComponentMode,
               true, VssBackupType.Full, false);
         // From here we just need to send messages to each writer that our
         // snapshot is imminent,
         using (IVssAsync async = _backup.PrepareForBackup())
         {
            // As before, the 'using' statement automatically disposes of
            // our comm link.  Also as before, we simply block while the
            // writers to complete their background preparations.
            async.Wait();
         }
         // It's now time to create the snapshot.  Each writer will have to
         // freeze its I/O to the selected volumes for up to 10 seconds
         // while this process takes place.
         _snap.Copy();
      }
      /// <summary>
      /// This simple method uses a bit of string manipulation to turn a
      /// full, local path into its corresponding snapshot path.  This
      /// method may help users perform full file copies from the snapsnot.
      /// </summary>
      /// <remarks>
      /// Note that the System.IO methods are not able to access files on
      /// the snapshot.  Instead, you will need to use the AlphaFS library
      /// as shown in the example.
      /// </remarks>
      /// <example>
      /// This code creates a shadow copy and copies a single file from
      /// the new snapshot to a location on the D drive.  Here we're
      /// using the AlphaFS library to make a full-file copy of the file.
      /// <code>
      /// string source_file = @"C:'Windows'system32'config'sam";
      /// string backup_root = @"D:'Backups";
      /// string backup_path = Path.Combine(backup_root,
      ///       Path.GetFilename(source_file));
      ///
      /// // Initialize the shadow copy subsystem.
      /// using (VssBackup vss = new VssBackup())
      /// {
      ///    vss.Setup(Path.GetPathRoot(source_file));
      ///    string snap_path = vss.GetSnapshotPath(source_file);
      /// 
      ///    // Here we use the AlphaFS library to make the copy.
      ///    Alphaleonis.Win32.Filesystem.File.Copy(snap_path, backup_path);
      /// }
      /// </code>
      /// </example>
      /// <seealso cref="GetStream"/>
      /// <param name="localPath">The full path of the original file.</param>
      /// <returns>A full path to the same file on the snapshot.</returns>
      public string GetSnapshotPath(string localPath)
      {
         Trace.WriteLine("New volume: " + _snap.Root);
         // This bit replaces the file's normal root information with root
         // info from our new shadow copy.
         if (Path.IsPathRooted(localPath))
         {
            string root = Path.GetPathRoot(localPath);
            localPath = localPath.Replace(root, String.Empty);
         }
         string slash = Path.DirectorySeparatorChar.ToString();
         if (!_snap.Root.EndsWith(slash) && !localPath.StartsWith(slash))
            localPath = localPath.Insert(0, slash);
         localPath = localPath.Insert(0, _snap.Root);
         Trace.WriteLine("Converted path: " + localPath);
         return localPath;
      }
      /// <summary>
      /// This method opens a stream over the shadow copy of the specified
      /// file.
      /// </summary>
      /// <example>
      /// This code creates a shadow copy and opens a stream over a file
      /// on the new snapshot volume.
      /// <code>
      /// string source_file = @"C:'Windows'system32'config'sam";
      /// 
      /// // Initialize the shadow copy subsystem.
      /// using (VssBackup vss = new VssBackup())
      /// {
      ///    vss.Setup(Path.GetPathRoot(filename));
      ///    
      ///    // We can now access the shadow copy by either retrieving a stream:
      ///    using (Stream s = vss.GetStream(filename))
      ///    {
      ///       Debug.Assert(s.CanRead == true);
      ///       Debug.Assert(s.CanWrite == false);
      ///    }
      /// }
      /// </code>
      /// </example>
      public System.IO.Stream GetStream(string localPath)
      {
         // GetSnapshotPath() returns a very funky-looking path.  The
         // System.IO methods can't handle these sorts of paths, so instead
         // we're using AlphaFS, another excellent library by Alpha Leonis.
         // Note that we have no 'using System.IO' at the top of the file.
         // (The Stream it returns, however, is just a System.IO stream.)
         return File.OpenRead(GetSnapshotPath(localPath));
      }
      /// <summary>
      /// The final phase of the backup involves some cleanup steps.
      /// If we're in component mode, we're supposed to notify each of the
      /// writers of the outcome of the backup.  Once that's done, or if
      /// we're not in component mode, we send the BackupComplete event to
      /// all of the writers.
      /// </summary>
      /// <param name="succeeded">Success value for all of the writers.</param>
      void Complete(bool succeeded)
      {
         if (ComponentMode)
         {
            // As before, we iterate through all of the writers on the system.
            // A more efficient method might only iterate through those writers
            // that were actually involved in this backup.
            IList<IVssExamineWriterMetadata> writers = _backup.WriterMetadata;
            foreach (IVssExamineWriterMetadata metadata in writers)
            {
               foreach (IVssWMComponent component in metadata.Components)
               {
                  // The BackupSucceeded call should mirror the AddComponent
                  // call that was called during the discovery phase.
                  _backup.SetBackupSucceeded(
                        metadata.InstanceId, metadata.WriterId,
                        component.Type, component.LogicalPath,
                        component.ComponentName, succeeded);
               }
            }
            // Finally, we can dispose of the writer metadata.
            _backup.FreeWriterMetadata();
         }
         try
         {
            // The BackupComplete event must be sent to all of the writers.
            using (IVssAsync async = _backup.BackupComplete())
               async.Wait();
         }
         // Not sure why, but this throws a VSS_BAD_STATE on XP and W2K3.
         // Per some forum posts about this, I'm just ignoring it.
         catch (VssBadStateException) { }
      }
      /// <summary>
      /// This method takes the information in a file description and
      /// converts it to a full path specification - with wildcards.
      /// </summary>
      /// <remarks>
      /// Using the wildcard-to-regex library found at
      /// http://www.codeproject.com/KB/string/wildcmp.aspx on the
      /// output of this method might be very helpful.
      /// </remarks>
      /// <param name="file">Object describing a component's file.</param>
      /// <returns>
      /// Returns a full path, potentially including DOS wildcards.  Eg.
      /// 'c:'windows'config'*'.
      /// </returns>
      string FileToPathSpecification(VssWMFileDescription file)
      {
         // Environment variables (eg. "%windir%") are common.
         string path = Environment.ExpandEnvironmentVariables(file.Path);
         // Use the alternate location if it's present.
         if (!String.IsNullOrEmpty(file.AlternateLocation))
            path = Environment.ExpandEnvironmentVariables(
                  file.AlternateLocation);
         // Normalize wildcard usage.
         string spec = file.FileSpecification.Replace("*.*", "*");
         // Combine the file specification and the directory name.
         return Path.Combine(path, file.FileSpecification);
      }
   }
}