FileSystemWatcher. This class monitors a directory for changes. A program may need to process new files (often written to the directory by other programs).
Many features. FileSystemWatcher provides a way to monitor a directory for file changes, creations, deletions and renames. We do not need Windows Forms to use it.
A console program. This program uses a FileSystemWatcher static field. We initialize it with the new keyword in Init(). We add its Changed event handler.
Note Changed is triggered when a file in the directory is changed. It may execute twice per edit.
Note 2 To prevent duplicate work, it is a good idea to use a flag bool to indicate what happened—so we just set "needs update" to true.
using System;
using System.IO;
class Program
{
static void Main()
{
Console.WriteLine("MAIN");
Init();
// Run an infinite loop.
while (true)
{
Console.WriteLine("TYPE SOMETHING");
string line = Console.ReadLine();
Console.WriteLine("TYPED: " + line);
}
}
/// <summary>/// Watcher./// </summary>
static FileSystemWatcher _watcher;
/// <summary>/// Init./// </summary>
static void Init()
{
Console.WriteLine("INIT");
string directory = @"C:\programs\";
Program._watcher = new FileSystemWatcher(directory);
Program._watcher.Changed +=
new FileSystemEventHandler(Program._watcher_Changed);
Program._watcher.EnableRaisingEvents = true;
Program._watcher.IncludeSubdirectories = true;
}
/// <summary>/// Handler./// </summary>
static void _watcher_Changed(object sender, FileSystemEventArgs e)
{
Console.WriteLine("CHANGED, NAME: " + e.Name);
Console.WriteLine("CHANGED, FULLPATH: " + e.FullPath);
// Can change program state (set invalid state) in this method.// ... Better to use insensitive compares for file names.
}
}MAIN
INIT
TYPE SOMETHING
test
TYPED: test
TYPE SOMETHING
CHANGED, NAME: file.txt
CHANGED, FULLPATH: C:\programs\file.txt
CHANGED, NAME: file.txt
CHANGED, FULLPATH: C:\programs\file.txt
hello
TYPED: hello
TYPE SOMETHING
CHANGED, NAME: file.txt
CHANGED, FULLPATH: C:\programs\file.txt
CHANGED, NAME: file.txt
CHANGED, FULLPATH: C:\programs\file.txtHELLO WORLD!
X2
X3
Windows Forms tutorial. Before you can write any code, you must set up your Windows Forms program properly. Open the Toolbox and double-click on the FileSystemWatcher icon.
Then In the bottom tray, select Properties on the fileSystemWatcher1 label. You can specify the directory you want to monitor for changes.
Detail We use a directory named C:\watch. Next in the Properties panel, click on the lightning bolt and add 4 event handlers.
Info Once the program is run, you can change files in the C:\watch directory and dialog boxes will display the events.
using System.IO;
using System.Windows.Forms;
namespace WindowsFormsApplication1
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
void fileSystemWatcher1_Changed(object sender, FileSystemEventArgs e)
{
// Occurs when the contents of the file change.
MessageBox.Show(string.Format("Changed: {0} {1}", e.FullPath, e.ChangeType));
}
void fileSystemWatcher1_Created(object sender, FileSystemEventArgs e)
{
// FullPath is the new file's path.
MessageBox.Show(string.Format("Created: {0} {1}", e.FullPath, e.ChangeType));
}
void fileSystemWatcher1_Deleted(object sender, FileSystemEventArgs e)
{
// FullPath is the location of where the file used to be.
MessageBox.Show(string.Format("Deleted: {0} {1}", e.FullPath, e.ChangeType));
}
void fileSystemWatcher1_Renamed(object sender, RenamedEventArgs e)
{
// FullPath is the new file name.
MessageBox.Show(string.Format("Renamed: {0} {1}", e.FullPath, e.ChangeType));
}
}
}
A problem. You may have a problem with receiving multiple Changed events for a single file change. This must be due to a technical detail about how some programs write files.
Note You may need special code to filter Changed events. This depends on your application.
Timer. One of my favorite techniques for monitoring a program for changes is using a Timer instance and simply doing a scan on a regular interval.
And In this way, you could simply scan a directory every five seconds for changes.
Also You can then call methods based on the changed detected. You could use the FileInfo type as well as the Timer type for this.
A summary. We examined the FileSystemWatcher class. This type presents an excellent way to persistently monitor a directory for changes, without lots of custom code.
Dot Net Perls is a collection of tested code examples. Pages are continually updated to stay current, with code correctness a top priority.
Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.
This page was last updated on May 22, 2023 (edit).
