详解C#如何监控选定文件夹中文件的变动情况

namespace FileSystemWatcherDemo
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
​
        private void button1_Click(object sender, EventArgs e)
        {
​
            // 创建一个 FolderBrowserDialog 实例
            FolderBrowserDialog folderBrowserDialog = new FolderBrowserDialog();
​
            // 设置对话框的标题
            folderBrowserDialog.Description = "选择文件夹";
​
            // 如果用户点击了“确定”按钮
            if (folderBrowserDialog.ShowDialog() == DialogResult.OK)
            {
                richTextBox1.Text = "";
                // 获取用户选择的文件夹路径
                string selectedFolder = folderBrowserDialog.SelectedPath;
​
                // 提示被监控文件夹路径
                richTextBox1.Text += $"被监控的文件夹为：{selectedFolder}\r\n";
​
                var watcher = new FileSystemWatcher($"{selectedFolder}");
               
                watcher.NotifyFilter = NotifyFilters.Attributes
                                | NotifyFilters.CreationTime
                                | NotifyFilters.DirectoryName
                                | NotifyFilters.FileName
                                | NotifyFilters.LastAccess
                                | NotifyFilters.LastWrite
                                | NotifyFilters.Security
                                | NotifyFilters.Size;
​
                watcher.Changed += OnChanged;
                watcher.Created += OnCreated;
                watcher.Deleted += OnDeleted;
                watcher.Renamed += OnRenamed;
                
                watcher.Filter = "*.txt";
                watcher.IncludeSubdirectories = true;
                watcher.EnableRaisingEvents = true;
            }
            else
            {
                MessageBox.Show("您本次没有选择文件夹！！！");
            }
          
​
           
   
        }
​
        private void AppendMessageToRichTextBox(string message)
        {
            // 在RichTextBox中添加提示信息        
            richTextBox1.Invoke(new Action(() =>
            {
                richTextBox1.AppendText(message + Environment.NewLine);
            }));
        }
​
        private void OnChanged(object sender, FileSystemEventArgs e)
        {
            if (e.ChangeType != WatcherChangeTypes.Changed)
            {
                return;
            }
            AppendMessageToRichTextBox($"Changed: {e.FullPath}");
        }
​
        private void OnCreated(object sender, FileSystemEventArgs e)
        {
            string value = $"Created: {e.FullPath}";
            AppendMessageToRichTextBox($"Created: {e.FullPath}");
        }
​
        private  void OnDeleted(object sender, FileSystemEventArgs e)
        {
            AppendMessageToRichTextBox($"Deleted: {e.FullPath}");
        }
​
        private  void OnRenamed(object sender, RenamedEventArgs e)
        {       
            AppendMessageToRichTextBox($"Renamed:");
            AppendMessageToRichTextBox($"    Old: {e.OldFullPath}");
            AppendMessageToRichTextBox($"    New: {e.FullPath} ");           
        }
     
    }
}

 var watcher = new FileSystemWatcher($"{selectedFolder}");

watcher.Filter = "*.txt";

 watcher.IncludeSubdirectories = true;

 watcher.EnableRaisingEvents = true;

 watcher.NotifyFilter = NotifyFilters.Attributes
                                | NotifyFilters.CreationTime
                                | NotifyFilters.DirectoryName
                                | NotifyFilters.FileName
                                | NotifyFilters.LastAccess
                                | NotifyFilters.LastWrite
                                | NotifyFilters.Security
                                | NotifyFilters.Size;

[System.Flags]
public enum NotifyFilters

                watcher.Changed += OnChanged;
                watcher.Created += OnCreated;
                watcher.Deleted += OnDeleted;
                watcher.Renamed += OnRenamed;

 watcher.Changed += OnChanged;

/// <devdoc>
///    Occurs when a file or directory in the specified <see cref='System.IO.FileSystemWatcher.Path'/> is changed.
/// </devdoc>
public event FileSystemEventHandler? Changed
{
    add
    {
        _onChangedHandler += value;
    }
    remove
    {
        _onChangedHandler -= value;
    }
}

 public delegate void FileSystemEventHandler(object sender, FileSystemEventArgs e);

public class FileSystemEventArgs : EventArgs
{
     private readonly WatcherChangeTypes _changeType;
     private readonly string? _name;
     private readonly string _fullPath;
     /// <devdoc>
///    Gets one of the <see cref='System.IO.WatcherChangeTypes'/> values.
/// </devdoc>
public WatcherChangeTypes ChangeType
{
    get
    {
        return _changeType;
    }
}
​
/// <devdoc>
///    Gets the fully qualified path of the affected file or directory.
/// </devdoc>
public string FullPath
{
    get
    {
        return _fullPath;
    }
}
​
​
/// <devdoc>
///       Gets the name of the affected file or directory.
/// </devdoc>
public string? Name
{
    get
    {
        return _name;
    }
}
 }

 //
 // 摘要:
 //     Changes that might occur to a file or directory.
 [Flags]
 public enum WatcherChangeTypes
 {
     //
     // 摘要:
     //     The creation of a file or folder.
     Created = 1,
     //
     // 摘要:
     //     The deletion of a file or folder.
     Deleted = 2,
     //
     // 摘要:
     //     The change of a file or folder. The types of changes include: changes to size,
     //     attributes, security settings, last write, and last access time.
     Changed = 4,
     //
     // 摘要:
     //     The renaming of a file or folder.
     Renamed = 8,
     //
     // 摘要:
     //     The creation, deletion, change, or renaming of a file or folder.
     All = 15
 }

watcher.Changed += OnChanged;

  private void OnChanged(object sender, FileSystemEventArgs e)
  {
      if (e.ChangeType != WatcherChangeTypes.Changed)
      {
          return;
      }
      AppendMessageToRichTextBox($"Changed: {e.FullPath}");
  }

 private void OnChanged(object sender, FileSystemEventArgs e)

 public delegate void FileSystemEventHandler(object sender, FileSystemEventArgs e);

 /// <devdoc>
 ///    Raises the <see cref='System.IO.FileSystemWatcher.Changed'/> event.
 /// </devdoc>
 protected void OnChanged(FileSystemEventArgs e)
 {
     InvokeOn(e, _onChangedHandler);
 }
 private void InvokeOn(FileSystemEventArgs e, FileSystemEventHandler? handler)
 {
     if (handler != null)
     {
         ISynchronizeInvoke? syncObj = SynchronizingObject;
         if (syncObj != null && syncObj.InvokeRequired)
             syncObj.BeginInvoke(handler, new object[] { this, e });
         else
             handler(this, e);
     }
 }