From Forum Nokia Wiki

ID	TSS001474	Creation date	October 30, 2009
Platform	S60 5th Edition	Devices	Nokia 5800 XPressMusic
Category	Qt for Symbian	Subcategory	QtCore, Files/Data

Keywords (APIs, classes, methods, functions): QFileSystemWatcher

Description

This article provides a way for a Qt application to monitor the file system for changes to files and directories by watching a list of specified paths.

Solution

Multiple files and/or directories can be monitored by providing their paths to the QFileSystemWatcher instance and connecting the directoryChanged() and fileChanged() signals to slot functions that handle the events of modifying or removing a file and a directory, respectively.

Watching for changes in the file system

// Constructing QFileSystemWatcher
 QString pathToWatch;
 m_watcher = new QFileSystemWatcher( this ); // pass this (QObject) as parent
 
 // Watching for changes in the default location for pictures
 pathToWatch.append( QDesktopServices::storageLocation( QDesktopServices::PicturesLocation ) );
 m_watcher->addPath( pathToWatch );
 
 //Adding another path, watching for changes in specified file 
 m_watcher->addPath( pathToWatch + "someImage.jpg" );
 
 // Connect signals to our slots
 connect( m_watcher, SIGNAL( directoryChanged ( const QString& ) ), 
          this, SLOT( trackChanged( const QString ) ) );
 
 connect( m_watcher, SIGNAL( fileChanged ( const QString& ) ), 
          this, SLOT( trackChanged( const QString ) ) );

Slot implementation

In the following code, FileWatcher is our own class, derived from QObject. A change log is simply written to a file.

void FileWatcher::trackChanged( const QString & entry )
 {
   log( path );
 }

Logging the changes into a file

#include <QFile>
  #include <QFileInfo>
  #include <QTextStream>
  #include <QDateTime>

void MainWindow::log( const QString & entry )
   {
     QFile file("c:\\data\\LogFileSystemChanges.txt");
 
     if ( !file.open( QIODevice::Append | QIODevice::Text ) )
       return;
 
     QTextStream out( &file );
     QFileInfo info( entry );
 
     if( info.isDir() ) {
       out << "Dir ";
     } else {
       out << "File ";
     }
 
     if( info.exists() ) {
       out << "changed: ";
     } else {
       out << "removed: ";
     }
 
     QString format("dd.MM.yyyy/hh:mm:ss.zzz");
     out << QDateTime::currentDateTime().toString(format) << ":\t" << entry << "\n";
 
     file.close();
   }

Note

The act of monitoring files and directories for modifications consumes system resources. This implies that there is a limit to the number of files and directories that your process can monitor simultaneously.