临视目录内容是否有改变的解读



http://s.codeproject.com/Articles/271669/Using-FileSystemWatcher-to-monitor-multiple-direct

Using FileSystemWatcher to monitor multiple directories

There are times that we need to monitor multiple directories and if any changes are available, invoke a given method.

In a previous example, I have showed how to use the FileSystemWatcher class to monitor a directory. But there are times that we need to monitor multiple directories and if any changes are available, invoke a given method.

We can do that by using the following method. First create a class. We’ll call this classWatcher.

   1: public class Watcher
   2:     {
   3:  
   4:         public string Directory { get; set; }
   5:         public string  Filter { get; set; }
   6:  
   7:  
   8:         private Delegate _changeMethod;
   9:  
  10:         public Delegate ChangeMethod
  11:         {
  12:             get { return _changeMethod; }
  13:             set { _changeMethod = value; }
  14:         }
  15:         
  16:         FileSystemWatcher fileSystemWatcher = new FileSystemWatcher();
  17:  
  18:         public Watcher(string directory, string filter, Delegate invokeMethod)
  19:         {
  20:             this._changeMethod = invokeMethod;
  21:             this.Directory = directory;
  22:             this.Filter = Filter;
  23:         }
  24:  
  25:  
  26:         public void StartWatch()
  27:         {
  28:             
  29:             
  30:             fileSystemWatcher.Filter = this.Filter;
  31:             fileSystemWatcher.Path = this.Directory;
  32:             fileSystemWatcher.EnableRaisingEvents = true;
  33:  
  34:             fileSystemWatcher.Changed += 
                    new FileSystemEventHandler(fileSystemWatcher_Changed);
  35:         }
  36:  
  37:         void fileSystemWatcher_Changed(object sender, FileSystemEventArgs e)
  38:         {
  39:             if (_changeMethod != null)
  40:             {
  41:                 _changeMethod.DynamicInvoke(sender, e);
  42:             }
  43:         }
  44:     }

And we can use it to monitor multiple directories as shown below (for this example, I have used a console application and I am only considering the change event):

   1: class Program
   2:     {
   3:         delegate void invokeMethodDelegate(object sender, FileSystemEventArgs e);
   4:  
   5:         static void Main(string[] args)
   6:         {
   7:             
   8:             invokeMethodDelegate mymethod = new invokeMethodDelegate(InvokeMethod);  //公用的全局函数
   9:             Watcher w1 = new Watcher(@"C:\Directory1", "*.*", mymethod); //这里先后创建两个监视对象，指向共同的全局函数
  10:             w1.StartWatch();
  11:  
  12:             Watcher w2 = new Watcher(@"D:\Directory2", "*.*", mymethod);
  13:             w2.StartWatch();
  14:  
  15:             string zRetVal = Console.ReadLine();
  16:  
  17:            
  18:         }
  19:  
  20:         static  void InvokeMethod(object sender, FileSystemEventArgs e)//公用的全局函数
  21:         {
  22:             Console.WriteLine("Change in file {0}", e.FullPath);
  23:         }
  24:     }

所以，看到C#的事件机制，还是比较让人感觉亲切。