• Download the Visual Basic 6.0 Example - 5.39 Kb
• Download the source code - 18.5 Kb
• Download the DLL - 27.3 Kb

Introduction

This project makes it possible to monitor your directories and/or your files. The control will generate an event whenever a file or subdirectory is created, updated or deleted.

If you want to know how you can use this control in a MFC application, then look at the page: How to use an ATL-control with MFC.

I've written this project in Visual C++ 6.0 with ATL 3.0, because you can't use multithreading in Visual Basic.

Properties

Methods

Events

Remarks

It's recommended that you first add all the directories you want to monitor before you start monitoring, because when the monitor is running, it will always be stopped and started again when you add a new directory.

The control was tested on Windows NT and Windows 98.

The control is written with Visual C++ 6.0 using ATL 3.0. The control was tested with Visual Basic 6.0

Resources

These are the resources I've used to create this project:

1. PRB: Firing Event in Second Thread Causes IPF or GPF

Because I use multithreading in this control and it's not possible to fire an event from within a thread, I used the following trick to fire the event.

The control is created as a window. I pass a pointer of the control to the thread function where I can use the window handle of the control to send a message. This message will be handled and will fire the event to the container of the control.

class ATL_NO_VTABLE CWatch : 
    public CWindowImpl<CWatch>, // The control is implemented as a window
    public CComObjectRootEx<CComSingleThreadModel>,
    public CComCoClass<CWatch, &CLSID_Watch>,
    public IConnectionPointContainerImpl<CWatch>,
    public IDispatchImpl<IWatch, &IID_IWatch, &LIBID_FILEMONITOR>,
    public CProxy_IWatchEvents< CWatch >
{
public:
    CWatch()
    {
        m_bStarted = false;
        m_hEvent = NULL;
        m_hThread = NULL;
    }
    deqString m_Paths;
    HANDLE m_hEvent;
    HANDLE m_hThread;
    DWORD m_dwThreadId;
    bool m_bStarted;
    cstring m_sNotify;

DECLARE_WND_CLASS(TEXT("Watch"))
BEGIN_MSG_MAP(CWatch)
    MESSAGE_HANDLER(WM_WATCH_NOTIFY, OnWatchNotify) // The messagehandler
END_MSG_MAP()

    LRESULT OnWatchNotify(UINT uMsg, WPARAM wParam, 
        LPARAM lParam, BOOL &bHandled)    // Fires the Notify event
    {
        Fire_Notify(_bstr_t(m_sNotify.c_str()), wParam);
        return 0;
    }
    ...
};

The thread is created as follows in the Start method:

m_hThread = CreateThread(NULL, 0, ThreadFunc, (LPVOID) this, 0, &m_dwThreadId);

As you can see, I pass the this-pointer to the ThreadFunc.

Updates

• 11 May 2000 - fixed a bug in the AddPath-method
• 12 Dec 2000 - The major change is that the thread for monitoring the directories is created only once.

  In the past, the thread was recreated when you added or removed a path. Now I use an event to notify the thread. When the thread receives the event, it will automatically refresh the FileNotifications.

  Check my website for updates.