How to get a notification if change occurs in a specified directory

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Introduction

Sometimes, its is very important to monitor events, occurring in some directory. For example, if new file was saved in a specified directory, the application must to do something.

Background

File system notification events can be obtained by the Win32 API function FindFirstChangeNotification (look more in detail in the MSDN). This function creates a change notification handle and sets up initial change notification filter conditions. A wait on a notification handle succeeds when a change matching the filter conditions occurs in the specified directory or subtree. After the wait has been satisfied, the application can respond to this condition and continue monitoring the directory, by calling the FindNextChangeNotification function and the appropriate wait function. When the handle is no longer needed, it can be closed by using the FindCloseChangeNotification function.

The classes

CNotifyDirCheck class holds notification events in the work thread and parse file tree for finding a new (changed) file. User must override the Action function of the base class or implement own notification callback. This callback has the following prototype:

UINT DefaultNotificationCallback(
CFileInformation fiObject,  //file (directory) information object
EFileAction       faAction,  //notification event type
LPVOID           lpData );  //user's data pointer

If the callback succeeds, the return value is 0. If the callback failed, the return value must be an error number (>0). Samples of the callback and virtual function Action exists in the code of the class CNotifyDirCheck.

Class CFileInformation is a useful API wrapping class that is developed to make file manipulation and to obtain information about files and directories in a simpler and easier way.

How to Use

1. Create an object of CNotifyDirCheck.
2. Create notification callback or override virtual function Action.
3. Select directory.
4. Add the user’s data pointer (if needed).
5. Call method Run to start notification thread.
6. Call method Stop to stop notification thread (or this method will be called in destructor).

CNotifyDirCheck m_ndc;
…
UINT DirCallback(...) {...}
...
m_ndc.SetDirectory( m_dir );//root directory
m_ndc.SetData( this );//user’s data
m_ndc.SetActionCallback( DirCallback );//user’s callback
…
m_ndc.Run();//start workthread
...
m_ndc.Stop();//stop workthread

Conclusion

I would like to mention thanks to CodeProject authors for many great ideas and useful source code. I'd be glad if somebody uses my class. Please let me know of any bugs that you have found and I will fix them in a future release.

References

1. MSDN
2. CodeProject - Files & Folders

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