如何在FileSystemWatcher类变更事件触发错误时通知主窗体？

我有一个窗体，调用某类创建FileSystemWatcher，该类会在FileSystemWatcher触发时执行各类操作。当FileSystemWatcher的Changed事件执行过程中发生错误时，我需要通知主窗体出现问题。

我的FileSystemWatcher类代码如下：

internal static class PpsTransactionFileWatcher
{
  private static FileSystemWatcher _watcher;

  public static Suburban.Miscellaneous.Response StartPpsFileWatcher()
  {
    var response = new Suburban.Miscellaneous.Response();
    response.IsSuccess = true;
    response.Message = "Success";

    try
    {
      CreateTrnFileWatcher();
      ProcessTransactionFile();
      return response;
    }
    catch (Exception ex)
    {
      LoggingWrapper.Log("StartPpsFileWatcher", ex.ToString(), ex);
      response.IsSuccess = false;
      response.Message = ex.Message;
      return response;
    }
  }

  private static void CreateTrnFileWatcher()
  {
    try
    {
      _watcher = new FileSystemWatcher
      {
        Path = GlobalSettings.PpsDirectory,
        NotifyFilter = NotifyFilters.LastWrite,
        Filter = GlobalSettings.PpsTransactionFile
      };

      _watcher.Changed += TrnWatcherChanged;
      _watcher.EnableRaisingEvents = true;
    }
    catch (Exception ex)
    {
      LoggingWrapper.Log("CreateTrnFileWatcher", ex.ToString(), ex);
      throw;
    }
  }


  private static void TrnWatcherChanged(object sender, FileSystemEventArgs e)
  {
    try
    {
      _watcher.Changed -= TrnWatcherChanged;
      ProcessTransactionFile();
      _watcher.Changed += TrnWatcherChanged;
    }
    catch (Exception ex)
    {
      LoggingWrapper.Log("TrnWatcherChanged", ex.ToString(), ex);
    }
  }
}

在窗体中我通过以下代码调用该类：

var transresponse = PpsTransactionFileWatcher.StartPpsFileWatcher();

请问如何在变更事件触发后，通知主窗体该类抛出的异常？

可以通过在静态类中定义静态事件的方式，让主窗体订阅该事件，当Changed事件中发生异常时触发事件通知窗体。

步骤1：修改PpsTransactionFileWatcher类，添加异常通知事件 #

在类中新增静态事件用于传递异常信息，然后在TrnWatcherChanged的捕获块中触发该事件：

internal static class PpsTransactionFileWatcher
{
  private static FileSystemWatcher _watcher;
  // 定义静态事件，用于向外通知异常
  public static event EventHandler<Exception> WatcherErrorOccurred;

  public static Suburban.Miscellaneous.Response StartPpsFileWatcher()
  {
    var response = new Suburban.Miscellaneous.Response();
    response.IsSuccess = true;
    response.Message = "Success";

    try
    {
      CreateTrnFileWatcher();
      ProcessTransactionFile();
      return response;
    }
    catch (Exception ex)
    {
      LoggingWrapper.Log("StartPpsFileWatcher", ex.ToString(), ex);
      response.IsSuccess = false;
      response.Message = ex.Message;
      return response;
    }
  }

  private static void CreateTrnFileWatcher()
  {
    try
    {
      _watcher = new FileSystemWatcher
      {
        Path = GlobalSettings.PpsDirectory,
        NotifyFilter = NotifyFilters.LastWrite,
        Filter = GlobalSettings.PpsTransactionFile
      };

      _watcher.Changed += TrnWatcherChanged;
      _watcher.EnableRaisingEvents = true;
    }
    catch (Exception ex)
    {
      LoggingWrapper.Log("CreateTrnFileWatcher", ex.ToString(), ex);
      throw;
    }
  }


  private static void TrnWatcherChanged(object sender, FileSystemEventArgs e)
  {
    try
    {
      _watcher.Changed -= TrnWatcherChanged;
      ProcessTransactionFile();
      _watcher.Changed += TrnWatcherChanged;
    }
    catch (Exception ex)
    {
      LoggingWrapper.Log("TrnWatcherChanged", ex.ToString(), ex);
      // 触发异常通知事件，传递捕获到的异常
      WatcherErrorOccurred?.Invoke(null, ex);
    }
  }
}

步骤2：在主窗体中订阅事件并处理通知 #

在窗体的初始化逻辑（比如Form_Load事件）中订阅异常事件，注意FileSystemWatcher的事件在非UI线程触发，需要通过Invoke切换到UI线程更新界面：

private void Form1_Load(object sender, EventArgs e)
{
    // 订阅异常通知事件
    PpsTransactionFileWatcher.WatcherErrorOccurred += PpsTransactionFileWatcher_WatcherErrorOccurred;
    // 启动文件监视器
    var transresponse = PpsTransactionFileWatcher.StartPpsFileWatcher();
}

private void PpsTransactionFileWatcher_WatcherErrorOccurred(object sender, Exception e)
{
    // 跨线程访问UI控件必须使用Invoke切换到UI线程
    if (this.InvokeRequired)
    {
        this.Invoke(new Action<object, Exception>(PpsTransactionFileWatcher_WatcherErrorOccurred), sender, e);
        return;
    }
    // 这里处理异常通知，比如弹出提示框
    MessageBox.Show($"文件监视器发生错误：{e.Message}", "错误提示", MessageBoxButtons.OK, MessageBoxIcon.Error);
}

补充优化 #

• 如果需要传递更多上下文信息（比如触发异常的文件路径），可以自定义事件参数类：

public class WatcherErrorEventArgs : EventArgs
{
    public Exception Error { get; set; }
    public string TriggerFilePath { get; set; }
}

然后修改事件定义为public static event EventHandler<WatcherErrorEventArgs> WatcherErrorOccurred;，触发时传递参数：

WatcherErrorOccurred?.Invoke(null, new WatcherErrorEventArgs { Error = ex, TriggerFilePath = e.FullPath });

• 窗体关闭时记得取消订阅事件，避免内存泄漏：

private void Form1_FormClosed(object sender, FormClosedEventArgs e)
{
    PpsTransactionFileWatcher.WatcherErrorOccurred -= PpsTransactionFileWatcher_WatcherErrorOccurred;
}

内容的提问来源于stack exchange，提问作者SomeoneSpecial