Hope, you are using Silverlight OOB(Out Of Browser) mode for all file handling operation becaz normal mode won't allow.
Regarding file manipulation events, you don't need to write your own event handler. In stead, you can use FileSystemWatcher class of System.IO namespace with the below built-in event handlers.
FileSystemWatcher watcher = new FileSystemWatcher();
watcher.Path = filePath;
watcher.NotifyFilter = NotifyFilters.LastAccess | NotifyFilters.LastWrite
| NotifyFilters.FileName | NotifyFilters.DirectoryName;
watcher.Filter = "*.txt";
watcher.Changed += new FileSystemEventHandler(OnChanged);
watcher.Created += new FileSystemEventHandler(OnChanged);
watcher.Deleted += new FileSystemEventHandler(OnChanged);
watcher.Renamed += new RenamedEventHandler(OnRenamed);