How to listen file change notification.

        When we want to receive a notifications about file system changes, we can use class FileSystemWatcher.

Code sample:

string testFolder = Path.GetTempPath();
string testFilePath = Path.Combine(testFolder, "test.tst");
File.Delete(testFilePath);

using (FileSystemWatcher watcher = new FileSystemWatcher(testFolder, "*.tst"))
{
    watcher.NotifyFilter = 
        NotifyFilters.LastAccess | NotifyFilters.LastWrite | 
        NotifyFilters.FileName | NotifyFilters.DirectoryName |
        NotifyFilters.CreationTime | NotifyFilters.Attributes |
        NotifyFilters.Size | NotifyFilters.Security;
    watcher.Created += OnFileChanged;
    watcher.Changed += OnFileChanged;
    watcher.Deleted += OnFileChanged;
    watcher.EnableRaisingEvents = true;

    File.WriteAllText(testFilePath, "text");
    File.AppendAllText(testFilePath, "additional text");
    File.Delete(testFilePath);
}

Output window content:

Notes:

Unfortunately, my experience shows, that FilesystemWatcher doesn't work absolutely correct. In many cases, it doesn't catch a file changing.

Reference:

FileSystemWatcher Class