如何用C#同步两个文件夹下的文件
如题。
比如将C盘的DATA目录及子目录下的文件同步备份到D盘的BAK目录下，为了节约时间，在上次备份后未修改过的文件不要复制，上次备份后新增的文件要添加，上次备份后删除的文件同步删除

------解决方案--------------------
FileSystemWatcher 
是啊，event知道吗，你也可以自己包装，添加event实现文件监视的功能

 封装原来的DirectoryInfo类，添加事件，可以代替FileSystemWatcher 类
using System;
using System.IO;

//封装原来的DirectoryInfo类，添加事件，可以代替FileSystemWatcher 类
public class DirectoryInfoNotify
{
public DirectoryInfoNotify(string path)
{
internalDirInfo = new DirectoryInfo(path);
}

private DirectoryInfo internalDirInfo = null;
public event EventHandler AfterCreate;
public event EventHandler AfterCreateSubDir;
public event EventHandler AfterDelete;
public event EventHandler AfterMoveTo;
protected virtual void OnAfterCreate()
{
EventHandler afterCreate = AfterCreate;
if (afterCreate != null)
{

afterCreate(this, new EventArgs());
}
}

protected virtual void OnAfterCreateSubDir()
{
EventHandler afterCreateSubDir = AfterCreateSubDir;
if (afterCreateSubDir != null)
{
afterCreateSubDir(this, new EventArgs());
}
}

protected virtual void OnAfterDelete()
{
EventHandler afterDelete = AfterDelete;
if (afterDelete != null)
{
afterDelete(this, new EventArgs());
}
}

protected virtual void OnAfterMoveTo()
{
EventHandler afterMoveTo = AfterMoveTo;
if (afterMoveTo != null)
{
afterMoveTo(this, new EventArgs());
}
}

// Event firing members
//激活事件的方法
public void Create()
{

internalDirInfo.Create();
OnAfterCreate();
}

public DirectoryInfoNotify CreateSubdirectory(string path)
{
DirectoryInfo subDirInfo = internalDirInfo.CreateSubdirectory(path);
OnAfterCreateSubDir();

return (new DirectoryInfoNotify(subDirInfo.FullName));
}

public void Delete(bool recursive)
{
internalDirInfo.Delete(recursive);
OnAfterDelete();
}

public void Delete()
{
internalDirInfo.Delete();
OnAfterDelete();
}

public void MoveTo(string destDirName)
{
internalDirInfo.MoveTo(destDirName);
OnAfterMoveTo();
}

// Nonevent firing members
public string FullName
{
get { return (internalDirInfo.FullName); }
}
public string Name
{
get { return (internalDirInfo.Name); }
}
public DirectoryInfoNotify Parent
{
get { return (new DirectoryInfoNotify(internalDirInfo.Parent.FullName)); }
}
public DirectoryInfoNotify Root
{
get { return (new DirectoryInfoNotify(internalDirInfo.Root.FullName)); }
}

public override string ToString()
{
return (internalDirInfo.ToString());
}
}