c# - FileWatcher 典型实现？

Question

我正在构建一个应用程序，我将在其中查看文件。我对编程很陌生，所以我(也许)没有什么问题，因为我没有真正的实践。我的程序可以正常工作，但我不知道在“真实”软件中通常是如何实现的。请概述和评论。因为我喜欢在 DateFiles 类中尽可能多，而在 MainViewModel 中尽可能少。是的，应用程序基于 MVVM 构建。

我目前的状态:

• 在我的 MainViewModel 中

  公共(public)静态字符串ConfigurationFilesSourcePath2;

  private void InitializeFiles()
  {
      // New instance of DateFiles
      DF = new DataFiles();
  
      // Path to DateFiles
      DF.ConfigurationFilesSourcePath = ConfigurationFilesSourcePath;
  
      // Run Initialization method to establish "filewatching"
      DF.InitializeFiles();
  
      // Refresh ListView in View
      RefreshFileList();
  
      // Assign a Handler to PropertyChanged event
      DF.PropertyChanged += DF_PropertyChanged;
  }
  
  // If something change inside DateFiles
  private void DF_PropertyChanged(object sender, PropertyChangedEventArgs e)
  {
      RefreshFileList();
  }
  
  // Refresh file list
  public void RefreshFileList()
  {
      fileslist = new ObservableCollection<Files>();
  
      foreach (var item in DF.fileslist)
      {
          fileslist.Add(item);
      }
  
      NotifyPropertyChanged("fileslist");
  }
  

• 数据文件类:

   public class DataFiles : ViewModelBase
   {
  public FileSystemWatcher filewatcher;
  public string ConfigurationFilesSourcePath;
  public ObservableCollection<Files> fileslist { get; set; } = new ObservableCollection<Files>();
  
  public void InitializeFiles()
  {
      // Create a new FileSystemWatcher
      filewatcher = new FileSystemWatcher();
  
      // Set filter to only catch XAL files
      filewatcher.Filter = "*.txt";
  
      // Set the path
      filewatcher.Path = ConfigurationFilesSourcePath;
  
      // Subscribe to the Created event
      filewatcher.Created += new FileSystemEventHandler(FileOnchanged);
      filewatcher.Changed += new FileSystemEventHandler(FileOnchanged);
      filewatcher.Deleted += new FileSystemEventHandler(FileOnchanged);
      filewatcher.Renamed += new RenamedEventHandler(FileOnRenamed);
  
      // Enable the FileSystemWatcher events
      filewatcher.EnableRaisingEvents = true;
  
      RefreshFilesList();
  }
  
  private void FileOnchanged(object sender, FileSystemEventArgs e)
  {
      RefreshFilesList();
  }
  
  private void FileOnRenamed(object sender, RenamedEventArgs e)
  {
      RefreshFilesList();
  }
  
  public void RefreshFilesList()
  {
      fileslist.Clear();
  
      DirectoryInfo dir = new DirectoryInfo(ConfigurationFilesSourcePath);
  
      string[] extensions = new[] { ".txt" };
  
      int nof = 0;
      foreach (FileInfo file in dir.GetFiles().Where(f => extensions.Contains(f.Extension.ToLower())).ToArray())
      {
          nof++;
  
          fileslist.Add(new Files()
          {
              FileId = nof,
              FileName = file.Name,
              FileChanged = file.LastWriteTime.ToString(),
              FileCreated = file.CreationTime.ToString(),
              OnlyNameWithoutExtension = Path.GetFileNameWithoutExtension(file.Name)
          });
          NotifyPropertyChanged("fileslist");
      }
  }
  

Answer 1

您的代码存在多个问题。其中最重要的是 - 你在每次更改时重建整个文件列表(而 FileSystemEventArgs 参数为你提供有关真正更改的内容和位置的信息)并且你不会在 UI 线程上更新你的 ObservableCollection。查看以下代码(但请记住，这只是您发现一些问题的示例):

public class DataFiles : IDisposable {
    public FileSystemWatcher filewatcher;
    private readonly object fileListLock = new object();
    // you don't need public setter on this
    public ObservableCollection<Files> Fileslist { get; } = new ObservableCollection<Files>();

    // pass path here, no need to use property
    public void InitializeFiles(string path) {
        // dispose existing watcher, if any
        DisposeWatcher();
        // Create a new FileSystemWatcher
        filewatcher = new FileSystemWatcher();
        // Set filter to only catch XAL files
        filewatcher.Filter = "*.txt";
        // Set the path
        filewatcher.Path = path;
        // Subscribe to the Created event
        filewatcher.Created += new FileSystemEventHandler(FileOnchanged);
        filewatcher.Changed += new FileSystemEventHandler(FileOnchanged);
        filewatcher.Deleted += new FileSystemEventHandler(FileOnchanged);
        filewatcher.Renamed += new RenamedEventHandler(FileOnRenamed);
        // don't RefreshFilesList on UI thread, that might take some time and will block UI
        Task.Run(() => RefreshFilesList());
        // Enable the FileSystemWatcher events
        filewatcher.EnableRaisingEvents = true;
    }

    private void FileOnchanged(object sender, FileSystemEventArgs e) {
        // lock here to avoid race conditions with RefreshFilesList
        lock (fileListLock) {
            // better use dictionary to avoid looping over all files
            // but looping is still much better than rebuilding whole list
            var file = Fileslist.FirstOrDefault(c => String.Equals(c.FullPath, e.FullPath, StringComparison.OrdinalIgnoreCase));
            if (file != null) {
                if (e.ChangeType == WatcherChangeTypes.Deleted)
                    ; // delete
                else
                    ; // update file properties
            }
            else {
                // add new, unless event is delete
            }
        }
    }

    private void FileOnRenamed(object sender, RenamedEventArgs e) {
        lock (fileListLock) {
            // better use dictionary to avoid looping over all files
            var file = Fileslist.FirstOrDefault(c => String.Equals(c.FullPath, e.OldFullPath, StringComparison.OrdinalIgnoreCase));
            if (file != null) {
                file.FullPath = e.FullPath;
            }
            else {
                // add new
            }
        }
    }

    public void RefreshFilesList() {
        // you need to lock here, because there is a race condition between this method and FileOnRenamed \ FileOnChanged, 
        // and you might lose some updates or get duplicates. 
        lock (fileListLock) {
            // update ObservableCollection on UI thread
            OnUIThreadDo(() => {
                Fileslist.Clear();
            });

            DirectoryInfo dir = new DirectoryInfo(filewatcher.Path);
            int nof = 0;

            var files = new List<Files>();
            // just use EnumerateFiles
            foreach (FileInfo file in dir.EnumerateFiles("*.txt")) {
                nof++;
                int tmp = nof;
                // if you are working with UI (that is most likely the case if you use ObservableCollection) -
                // you need to update that collection from UI thread if you have bound controls                    
                files.Add(new Files() {
                    FileId = tmp,
                    FullPath = file.FullName,
                    FileChanged = file.LastWriteTime,
                    FileCreated = file.CreationTime,
                });
                // don't do that
                // NotifyPropertyChanged("fileslist");
            }

            // publish them all to collection on UI thread
            OnUIThreadDo(() => {
                foreach (var file in files)
                    Fileslist.Add(file);
            });
        }
    }

    private void OnUIThreadDo(Action a) {
        if (Application.Current.CheckAccess())
            a();
        else
            Application.Current.Dispatcher.BeginInvoke(a);
    }

    public void Dispose() {
        DisposeWatcher();
    }

    private void DisposeWatcher() {
        if (filewatcher != null) {
            filewatcher.EnableRaisingEvents = false;
            filewatcher.Created -= FileOnchanged;
            filewatcher.Deleted -= FileOnchanged;
            filewatcher.Changed -= FileOnchanged;
            filewatcher.Renamed -= FileOnRenamed;
            filewatcher.Dispose();
        }
    }
}

public class Files : INotifyPropertyChanged
{ // implement INotifyPropertyChanged, because you need to reflect property changes in UI
    public int FileId { get; set; }
    public string FullPath { get; set; }
    public string FileName => Path.GetFileName(FullPath);
    public DateTime FileChanged { get; set; }
    public DateTime FileCreated { get; set; }
    public string OnlyNameWithoutExtension => Path.GetFileNameWithoutExtension(FullPath);
}