C# FileSystemWatcher 組件應用

    在ScheduledJob專案中，要用到很多自訂的DLL組件，為了保證啟動並執行效能，我們採用“緩衝”的方式對這些組件進行事先載入，待應用時在記憶體中既可找到對應的組件並運行，而無需每次都Load. 而這些組件隨時都可能有異動，可能新增，可能修改，此時要保證緩衝的內容也及時更新，就必須採取一種機制保證，這些組件表更時，能同時更新到記憶體緩衝中。

    在C#中我們可以採用FileSystemWatcher組件實現。

using System;using System.Collections.Generic;using System.IO;namespace fileSystemWatcherDemo{    /// <summary>    /// FileSystemWatcher 組件應用Demo 1    /// </summary>    class fileSystemWatcherDemo    {        private FileSystemWatcher dllWatcher;        static void Main(string[] args)        {            Console.WriteLine("file Watcher Started  at " + DateTime.Now.ToString());            fileSystemWatcherDemo watcher = new fileSystemWatcherDemo();            watcher.beginWatcher();            Console.Read();        }        private void beginWatcher()        {            dllWatcher = new FileSystemWatcher();            dllWatcher.Path = @"D:\ScheduledJob\DLL";            dllWatcher.IncludeSubdirectories = false;            dllWatcher.Filter = "*.*";            dllWatcher.NotifyFilter = NotifyFilters.LastWrite;            dllWatcher.EnableRaisingEvents = true;            dllWatcher.Changed += new FileSystemEventHandler(dllWatcher_Changed);        }        void dllWatcher_Changed(object sender, FileSystemEventArgs e)        {            try            {                Console.WriteLine("file" + e.FullPath + "was updated at " + DateTime.Now.ToString());            }            catch (Exception ex)            {                Console.WriteLine("file" + e.FullPath + "can't be updated at " + DateTime.Now.ToString() + ex.Message);            }        }    }}

測試下：運行後，在DLL檔案夾中丟一個123.txt,出現如下結果：

   

發現一個問題，丟一個檔案進去，OnChange事件觸發了多次（這裡是兩次），一個檔案也被解析執行了多次。

    目前這種情況還沒有找到徹底解決的辦法，而為了保證一次異動，changed事件只觸發一次，只能採取一些不是辦法的辦法來避免。根據這些多次觸發的事件是在短時間內完成的特點，這裡採用一個索引值對，鍵（檔案名稱）值（檔次執行的時間點）對來記錄一個檔案異動的時間，當再次觸發時，檢查這個索引值對，找到對應的檔案，看它上次執行的時間，如果在設定的特定的時間內，則返回，取消本次執行。

using System;using System.Collections.Generic;using System.IO;namespace fileSystemWatcherDemo{    /// <summary>    /// FileSystemWatcher 組é件t應|用?Demo    /// </summary>    class fileSystemWatcherDemo    {        private FileSystemWatcher dllWatcher;        //用於解決同一檔案一次異動的多次事件觸發問ê題a        private Dictionary<string, DateTime> watcherChangedTimes = null;        static void Main(string[] args)        {            Console.WriteLine("file Watcher Started  at " + DateTime.Now.ToString());            fileSystemWatcherDemo watcher = new fileSystemWatcherDemo();            watcher.beginWatcher();            Console.Read();        }        private void beginWatcher()        {            watcherChangedTimes = new Dictionary<string, DateTime>();            dllWatcher = new FileSystemWatcher();            dllWatcher.Path = @"D:\ScheduledJob\DLL";            dllWatcher.IncludeSubdirectories = false;            dllWatcher.Filter = "*.*";            dllWatcher.NotifyFilter = NotifyFilters.LastWrite;            dllWatcher.EnableRaisingEvents = true;            dllWatcher.Changed += new FileSystemEventHandler(dllWatcher_Changed);        }        void dllWatcher_Changed(object sender, FileSystemEventArgs e)        {            #region 60秒內同一個檔案只處理一次
DateTime now = DateTime.Now;            int reloadSeconds = 60;            if (watcherChangedTimes.ContainsKey(e.FullPath))            {                if (now.Subtract(watcherChangedTimes[e.FullPath]).TotalSeconds < reloadSeconds)                {                    return;                }                else                {                    watcherChangedTimes[e.FullPath] = now;                }            }            else            {                watcherChangedTimes.Add(e.FullPath, now);            }            #endregion            try            {               Console.WriteLine("file" + e.FullPath + "was updated at " + DateTime.Now.ToString());            }            catch (Exception ex)            {                Console.WriteLine("file" + e.FullPath + "can't be updated at " + DateTime.Now.ToString() + ex.Message);            }        }    }}

再丟一個檔案1.jpg進去，運行結果如下：