Home >> Files & Folders >> General CFileWatch By Herbert Griebel This class helps you to monitor files. You are notified if a file is modified outside the program.    VC6, W2K, MFC   Posted 13 Jun 2001 Articles by this author Send to a friend Printer friendly version

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Introduction

This class helps you to monitor files like in the DevStudio. If the file is modified outside your application a message box pops up and lets you choose between ignoring modifications or reloading the data, thus discarding all changes.

If the file is modified a message is sent either to the specified view or to the first view of a specified document. The message handler will call the reload function of the document class. The class should be thread safe.

Things you have to change in your View Class and Document Class:

In your document class header file:

class CFileWatchAppDoc : public CRichEditDoc
{
    ....
public:
    void OnFileReload();
protected:
    DWORD m_hFileWatch;
    void AddToFileWatch();
};

In your document class source file:

#include "FileWatch.h"

CFileWatchAppDoc::CFileWatchAppDoc()
{
    m_hFileWatch = NULL;
}

CFileWatchAppDoc::~CFileWatchAppDoc()
{
    CFileWatch::RemoveHandle(m_hFileWatch);
}

BOOL CFileWatchAppDoc::OnSaveDocument(LPCTSTR lpszPathName) 
{
    CFileWatch::RemoveHandle(m_hFileWatch);
    BOOL bSuccess = CRichEditDoc::OnSaveDocument(lpszPathName);
    AddToFileWatch();    
   return bSuccess;
}

void CFileWatchAppDoc::SetPathName(LPCTSTR lpszPathName, BOOL bAddToMRU)
{
    CFileWatch::RemoveHandle(m_hFileWatch);
    CRichEditDoc::SetPathName(lpszPathName, bAddToMRU);
    AddToFileWatch();
}

void CFileWatchAppDoc::AddToFileWatch()
{
    m_hFileWatch =  CFileWatch::AddFileFolder(lpszPathName,
                                               NULL, this);
    CFileWatch::SetAutoReload(m_hFileWatch,
        &((CYourApp*)AfxGetApp())->m_bAutoReloadDocTypeXY);
}

void CFileWatchAppDoc::OnFileReload()
{
    // your reload code
    ...
    UpdateAllViews(NULL);
}

In your view class header file:

class CFileWatchAppView : public CRichEditView
{
    ...
protected:
    //{{AFX_MSG(CFileWatchAppView)
    afx_msg LRESULT OnFileWatchNotification(WPARAM wParam, 
                                            LPARAM lParam);
    //}}AFX_MSG
    DECLARE_MESSAGE_MAP()
};    

In your view class source file:

#include "FileWatch.h"

BEGIN_MESSAGE_MAP(CFileWatchAppView, CRichEditView)
  //{{AFX_MSG_MAP(CFileWatchAppView)
  ON_REGISTERED_MESSAGE(CFileWatch::m_msgFileWatchNotify,
                        OnFileWatchNotification)
  //}}AFX_MSG_MAP
END_MESSAGE_MAP()

LRESULT CFileWatchAppView::OnFileWatchNotification(WPARAM wParam, 
                                                   LPARAM lParam)
{
    CString sPathName = CString((LPCTSTR)lParam);
    DWORD dwData = (DWORD)wParam;

   GetDocument()->OnFileReload();

    return 0;
}

In your mainframe class source file:

#include "FileWatch.h"

void CMainFrame::OnClose() 
{
    CFileWatch::Stop();

    CMDIFrameWnd::OnClose();
}

Add Non-document files to the watch:

#include "FileWatch.h"

void class::xy()
{
   ...
   DWORD hHandle = CFileWatch::AddFileFolder(LPCTSTR lpszFileName,
                HWND hWnd, CDocument* pDocument=NULL, DWORD dwData);
   ...
}

LRESULT CYourView::OnFileWatchNotification(WPARAM wParam, 
                                                   LPARAM lParam)
{
    CString sPathName = CString((LPCTSTR)lParam);
    DWORD dwData = (DWORD)wParam;

    if (sPathName == GetDocument()->GetPathName())
      GetDocument()->OnFileReload();
    else
    ...

    return 0;
}

Note: 

Not all file systems record write time in the same manner. For example, on Windows NT FAT, create time has a resolution of 10 milliseconds, write time has a resolution of 2 seconds, and access time has a resolution of 1 day (really, the access date). On NTFS, access time has a resolution of 1 hour. Furthermore, FAT records times on disk in local time, while NTFS records times on disk in UTC, so it is not affected by changes in time zone or daylight saving time. I have no information about the resolution of the write time in FAT or FAT32. However, if the file is modified several times in the same time window, only one notification can be detected!

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