【C#】FileSystemWatcherクラスの使い方と注意点

public partial class MainWindow : Window
{
    //FileSystemWatcherのオブジェクト名を設定
    System.IO.FileSystemWatcher watcher;
    public MainWindow()
    {
        InitializeComponent();

        Loaded += (s, e) =>
        {
            //監視するディレクトリの指定
            var directory = Environment.GetFolderPath(Environment.SpecialFolder.Desktop);

            //監視するディレクトリとファイルの種類を指定して初期化
            watcher = new System.IO.FileSystemWatcher(directory, "*.txt");

            //監視するフィールドの設定
            watcher.NotifyFilter =
                (NotifyFilters.Attributes
                | NotifyFilters.LastAccess
                | NotifyFilters.LastWrite
                | NotifyFilters.FileName
                | NotifyFilters.DirectoryName);

            //サブディレクトリは監視しない
            watcher.IncludeSubdirectories = false;

            //監視を開始する
            watcher.EnableRaisingEvents = true;
            Debug.WriteLine("Start!");

            //イベント設定
            watcher.Changed += new System.IO.FileSystemEventHandler(watcher_Changed);
            watcher.Created += new System.IO.FileSystemEventHandler(watcher_Changed);
            watcher.Deleted += new System.IO.FileSystemEventHandler(watcher_Changed);
            watcher.Renamed += new System.IO.RenamedEventHandler(watcher_Renamed);
        };
    }

    private void watcher_Created(object sender, FileSystemEventArgs e)
    {
        Debug.WriteLine("Created");
    }

    private DateTime lastWriteTimeSave = DateTime.Now;
    private void watcher_Changed(object sender, FileSystemEventArgs e)
    {
        Debug.WriteLine("Changed");

        //初回のみイベントを実行
        var file = new FileInfo(e.FullPath);
        if (file.LastWriteTime.Subtract(lastWriteTimeSave) < new TimeSpan(0, 0, 0, 1)) return;

        //メモ帳のプロセスをプロセスを強制的に終了させる
        Process[] ps = Process.GetProcessesByName("notepad");
        foreach (Process p in ps) p.Kill();

        //イベントを無効にする
        watcher.Changed -= watcher_Changed;

        //イベント発生元のファイルパスを取得しファイルを開く
        using (StreamWriter writer = new StreamWriter(e.FullPath, true, Encoding.GetEncoding("Shift_JIS")))
        {
            //文字を書き込む
            writer.WriteLine("sample write");
        };

        //更新日時を更新
        lastWriteTimeSave = file.LastWriteTime;

        //イベントを無効にする
        watcher.Changed += watcher_Changed;
    }

    private void watcher_Deleted(object sender, FileSystemEventArgs e)
    {
        Debug.WriteLine("Deleted");
    }

    private void watcher_Renamed(object sender, RenamedEventArgs e)
    {
        Debug.WriteLine("Renamed");
    }
}

private DateTime lastWriteTimeSave = DateTime.Now;
private void watcher_Changed(object sender, FileSystemEventArgs e)
{
    Debug.WriteLine("Changed");

    //初回のみイベントを実行
    var file = new FileInfo(e.FullPath);
    if (file.LastWriteTime.Subtract(lastWriteTimeSave) < new TimeSpan(0, 0, 0, 1)) return;
}