Question

所以我有一些代码可以递归地创建目录并分别下载文件夹中的文件。

以下是代码：

public class Program
    {
        static void UploadDownloadProgress(Object sender, FileDataTransferEventArgs e)
        { 
            // print a dot
            Console.WriteLine("Downloading");
            Console.WriteLine(".");
            // it's ok to go forward
            e.Cancel = false;
        } 

        public static void DownloadFolder(CloudStorage dropBoxStorage, ICloudDirectoryEntry remoteDir, string targetDir, string sourceDir)
        {           

            foreach (ICloudFileSystemEntry fsentry in remoteDir)
            {
                var filepath = Path.Combine(targetDir, fsentry.Name);

                if (fsentry is ICloudDirectoryEntry)
                {
                    Console.WriteLine("Created: {0}", filepath);
                    Directory.CreateDirectory(filepath);
                    DownloadFolder(dropBoxStorage, fsentry as ICloudDirectoryEntry, filepath, sourceDir);
                }
                else
                {
                    dropBoxStorage.DownloadFile(remoteDir, fsentry.Name, targetDir, UploadDownloadProgress);
                }
            }
        }

        static void Main(string[] args)
        {
            CloudStorage dropBoxStorage = new CloudStorage();

            var dropBixConfig = CloudStorage.GetCloudConfigurationEasy(nSupportedCloudConfigurations.DropBox);

            ICloudStorageAccessToken accessToken = null;

            using (FileStream fs = File.Open(@"C:\Users\Michael\token.txt", FileMode.Open, FileAccess.Read, FileShare.None))
            {
                accessToken = dropBoxStorage.DeserializeSecurityToken(fs);
            }

            var storageToken = dropBoxStorage.Open(dropBixConfig, accessToken);

            //do stuff
            //var root = dropBoxStorage.GetRoot();

            var publicFolder = dropBoxStorage.GetFolder("/Public");

            foreach (var folder in publicFolder)
            {
                Boolean bIsDirectory = folder is ICloudDirectoryEntry;

                Console.WriteLine("{0}: {1}", bIsDirectory ? "DIR" : "FIL", folder.Name);
            }

            string remoteDirName = @"/Public/IQSWS";
            string targetDir = @"C:\Users\Michael\";
            var remoteDir = dropBoxStorage.GetFolder(remoteDirName);

            DownloadFolder(dropBoxStorage, remoteDir, targetDir, remoteDirName);

            dropBoxStorage.Close();
        }

        public delegate void FileOperationProgressChanged(object sender, FileDataTransferEventArgs e);    
    }

在循环找到else中的第一个文件后，它会下载它，然后转到下一个文件，但它会在foreach上抛出异常：

System.InvalidOperationException was unhandled
  HResult=-2146233079
  Message=Collection was modified; enumeration operation may not execute.
  Source=mscorlib
  StackTrace:
       at System.Collections.Generic.Dictionary`2.ValueCollection.Enumerator.MoveNext()
       at StartServer.Program.DownloadFolder(CloudStorage dropBoxStorage, ICloudDirectoryEntry remoteDir, String targetDir, String sourceDir) in c:\Users\Michael\Documents\Visual Studio 2012\Projects\IQS Source\StartServer\StartServer\Program.cs:line 29
       at StartServer.Program.DownloadFolder(CloudStorage dropBoxStorage, ICloudDirectoryEntry remoteDir, String targetDir, String sourceDir) in c:\Users\Michael\Documents\Visual Studio 2012\Projects\IQS Source\StartServer\StartServer\Program.cs:line 39
       at StartServer.Program.DownloadFolder(CloudStorage dropBoxStorage, ICloudDirectoryEntry remoteDir, String targetDir, String sourceDir) in c:\Users\Michael\Documents\Visual Studio 2012\Projects\IQS Source\StartServer\StartServer\Program.cs:line 39
       at StartServer.Program.DownloadFolder(CloudStorage dropBoxStorage, ICloudDirectoryEntry remoteDir, String targetDir, String sourceDir) in c:\Users\Michael\Documents\Visual Studio 2012\Projects\IQS Source\StartServer\StartServer\Program.cs:line 39
       at StartServer.Program.Main(String[] args) in c:\Users\Michael\Documents\Visual Studio 2012\Projects\IQS Source\StartServer\StartServer\Program.cs:line 80
       at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()
  InnerException:

为什么会这样？为什么我所做的只是下载文件时编辑了数组？

Answer 1

您将整个集合remoteDir传递给DownloadFile方法，如下所示：

// AppLimit.CloudComputing.SharpBox.CloudStorage
public void DownloadFile(ICloudDirectoryEntry parent, string name, string targetPath, FileOperationProgressChanged delProgress)
{
    if (parent == null || name == null || targetPath == null)
    {
        throw new SharpBoxException(SharpBoxErrorCodes.ErrorInvalidParameters);
    }
    targetPath = Environment.ExpandEnvironmentVariables(targetPath);
    ICloudFileSystemEntry child = parent.GetChild(name);
    using (FileStream fileStream = new FileStream(Path.Combine(targetPath, name), FileMode.Create, FileAccess.Write, FileShare.None))
    {
        child.GetDataTransferAccessor().Transfer(fileStream, nTransferDirection.nDownload, delProgress, null);
    }
}

在此方法中唯一可以修改parent的点似乎是它调用GetChild的位置。看看GetChild（我用的是IlSpy）：

public ICloudFileSystemEntry GetChild(string name)
{
  return this.GetChild(name, true);
}

public ICloudFileSystemEntry GetChild(string name, bool bThrowException)
{
  this.RefreshResource();
  ICloudFileSystemEntry cloudFileSystemEntry;
  this._subDirectories.TryGetValue(name, out cloudFileSystemEntry);
  if (cloudFileSystemEntry == null && bThrowException)
  {
    throw new SharpBoxException(SharpBoxErrorCodes.ErrorFileNotFound);
  }
  return cloudFileSystemEntry;
}

反过来，这会在集合上调用RefreshResource。看起来像这样（假设了Dropbox实现）：

// AppLimit.CloudComputing.SharpBox.StorageProvider.BaseObjects.BaseDirectoryEntry
private void RefreshResource()
{
    this._service.RefreshResource(this._session, this);
    this._subDirectoriesRefreshedInitially = true;
}


// AppLimit.CloudComputing.SharpBox.StorageProvider.DropBox.Logic.DropBoxStorageProviderService
public override void RefreshResource(IStorageProviderSession session, ICloudFileSystemEntry resource)
{
    string resourceUrlInternal = this.GetResourceUrlInternal(session, resource);
    int num;
    string text = DropBoxRequestParser.RequestResourceByUrl(resourceUrlInternal, this, session, out num);
    if (text.Length == 0)
    {
        throw new SharpBoxException(SharpBoxErrorCodes.ErrorCouldNotRetrieveDirectoryList);
    }
    DropBoxRequestParser.UpdateObjectFromJsonString(text, resource as BaseFileEntry, this, session);
}

现在，这会调用UpdateObjectFromJsonString（我不会在这里粘贴，因为它很大），但这似乎更新了属于集合的resource对象。因此，您的收藏品会被更改......以及您的例外情况。

如果您对正在发生的事情感兴趣，我建议您将源代码下载到SharpBox或使用IlSpy来反汇编二进制文件。但简而言之，如果您以这种方式下载文件，它将修改集合。

也许使用其他DownloadFile重载之一，但不会传递整个集合。

Answer 2

不确定问题是否已经解决，但根据我的经验，修改集合需要您将IEnumerable对象强制转换为ToList（），以便它不会急切加载。

使用sharpbox下载文件

2 个答案: