一、背景
- 我们可以使用FileSystemWatcher监控文件系统，在特定的文件被创建、修改或删除时引发事件。
- 程序如下：
sing System;
using System.IO;
using System.Linq;
using System.Windows.Forms;
using System.Collections;
namespace MyNamespace
{
class MyClassCS
{
public Form1() {
InitializeComponent();
// 加载监控路径
string path1 = "D:\\1"; // 监控路径1
string[] pathArray = { path1 };
for (int i = 0; i < pathArray.Count(); i++) {
FileSystemWatcher watch = new FileSystemWatcher();
watch.Path = pathArray[i];
watch.Filter = "*";
watch.Created += new FileSystemEventHandler(OnChange);
watch.Changed += new FileSystemEventHandler(OnChange);
watch.Deleted += new FileSystemEventHandler(OnChange);
watch.EnableRaisingEvents = true;
// 监控文件名与上次写入时间
watch.NotifyFilter = NotifyFilters.FileName | NotifyFilters.LastWrite ;
}
listBox1.Items.Clear();
}
private void OnChange(object sender, FileSystemEventArgs e) {
if (e.ChangeType == WatcherChangeTypes.Changed || e.ChangeType == WatcherChangeTypes.Created) {
FileInfo fileInfo = new FileInfo(e.FullPath);
listBox1.Invoke(new MethodInvoker(delegate {
listBox1.Items.Add(DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss:ff") + ","
+ e.ChangeType + "," + e.FullPath
+ "," + fileInfo.LastWriteTime
+ "," + fileInfo.Length
);
}));
}
if (e.ChangeType == WatcherChangeTypes.Deleted) {
listBox1.Invoke(new MethodInvoker(delegate {
listBox1.Items.Add(DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss:ff") + "," + e.ChangeType + "," + e.FullPath);
}));
}
}
....
}
}
二、问题
- 让我们启动程序，并在监控目录中放入一个测试文件
- 我们惊奇地发现除了触发了一次Created事件外，还触发了两次Changed事件；
- 按照微软官方的解释：FileSystemWatcher监视的是操作系统活动，比如当文件拷贝到某一目录时，文件会进行多次缓冲写入，也就是会多次监控到NotifyFilters.LastWrite的变化，那就有可能会引发几个OnChanged以及OnCreated的事件。
三、解决技巧
- 文件拷贝完成后才进行捕获事件，确保文件能打开
- 已经放入目录中的文件，再次进行拷贝时，我们不希望再触发事件
- 为了保证以上两点，我们对程序进行改造
- 取消对Created事件的监控，只监控Changed事件
- 引入一个小技巧：即使触发了Changed事件，我们通过文件写读占打开的方式，判断文件是否已经复制完毕，
- 引入一个Hashtable，存放监控的文件列表，并显示
public partial class Form1 : Form {
// Hashtable：用于存放指定监控目录文件下新增、修改或删除的文件表，并可以去重
HashList dateTimeDictionary = new HashList();
// 显示监控列表
Thread thread ;
public Form1() {
InitializeComponent();
// 加载监控路径
string path1 = "D:\\1"; // 监控路径1
string[] pathArray = { path1};
for (int i = 0; i < pathArray.Count(); i++) {
FileSystemWatcher watch = new FileSystemWatcher();
watch.Path = pathArray[i];
watch.Filter = "*";
// 取消Created事件监控
//watch.Created += new FileSystemEventHandler(OnChange);
watch.Changed += new FileSystemEventHandler(OnChange);
watch.Deleted += new FileSystemEventHandler(OnChange);
watch.EnableRaisingEvents = true;
watch.NotifyFilter = NotifyFilters.FileName | NotifyFilters.LastWrite ;
}
listBox1.Items.Clear();
thread = new Thread(OnShowHashtable);//创建线程
thread.Start();
}
private void OnShowHashtable() {
while (true) {
Thread.Sleep(5000);
listBox2.Invoke(new MethodInvoker(delegate {
listBox2.Items.Clear();
foreach (var key in dateTimeDictionary.Keys) {
listBox2.Items.Add(key);
}
}));
}
}
private void OnChange(object sender, FileSystemEventArgs e) {
if (e.ChangeType == WatcherChangeTypes.Changed || e.ChangeType == WatcherChangeTypes.Created) {
FileInfo fileInfo = new FileInfo(e.FullPath);
try {
// 尝试打开文件，判断文件是否上传完毕
using (var fs = File.OpenWrite(e.FullPath)) {
}
if (!dateTimeDictionary.ContainsKey(e.FullPath)) {
dateTimeDictionary.Remove(e.FullPath);
dateTimeDictionary.Add(e.FullPath, fileInfo.LastWriteTime);
listBox1.Invoke(new MethodInvoker(delegate {
listBox1.Items.Add(DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss:ff") + ","
+ e.ChangeType + "," + e.FullPath
+ "," + fileInfo.LastWriteTime
+ "," + fileInfo.Length
);
}));
// ToDO
}
} catch (Exception) {
// 文件无法打开，等待
}
}
if (e.ChangeType == WatcherChangeTypes.Deleted) {
dateTimeDictionary.Remove(e.FullPath);
listBox1.Invoke(new MethodInvoker(delegate {
listBox1.Items.Add(DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss:ff") + "," + e.ChangeType + "," + e.FullPath);
}));
}
}
private void Form1_FormClosed(object sender, FormClosedEventArgs e) {
if (thread != null) {
thread.Abort();
}
}
}
