C# FileSystemWatcher 组件应用

    在ScheduledJob专案中，要用到很多自定义的DLL组件，为了保证运行的效能，我们采用“缓存”的方式对这些组件进行事先加载，待应用时在内存中既可找到对应的组件并运行，而无需每次都Load. 而这些组件随时都可能有异动，可能新增，可能修改，此时要保证缓存的内容也及时更新，就必须采取一种机制保证，这些组件表更时，能同时更新到内存缓存中。

    在C#中我们可以采用FileSystemWatcher组件实现。

using System;
using System.Collections.Generic;
using System.IO;

namespace fileSystemWatcherDemo
{
    /// <summary>
    /// FileSystemWatcher 组件应用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);
            }
        }
    }
}

测试下：运行后，在DLL文件夹中丢一个123.txt,出现如下结果：

   

发现一个问题，丢一个文件进去，OnChange事件触发了多次（这里是两次），一个文件也被解析执行了多次。

    目前这种情况还没有找到彻底解决的办法，而为了保证一次异动，changed事件只触发一次，只能采取一些不是办法的办法来避免。根据这些多次触发的事件是在短时间内完成的特点，这里采用一个键值对，键（文件名称）值（档次执行的时间点）对来记录一个文件异动的时间，当再次触发时，检查这个键值对，找到对应的文件，看它上次执行的时间，如果在设置的特定的时间内，则返回，取消本次执行。

using System;
using System.Collections.Generic;
using System.IO;

namespace fileSystemWatcherDemo
{
    /// <summary>
    /// FileSystemWatcher 组é件t应|用?Demo
    /// </summary>
    class fileSystemWatcherDemo
    {
        private FileSystemWatcher dllWatcher;

        //用于解决同一文件一次异动的多次事件触发问ê题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秒内同一个文件只处理一次
             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);
            }
        }
    }
}

再丢一个文件1.jpg进去，运行结果如下：