Windows Callback When The Active Window Changed

public class ActiveWindow
{
    public delegate void ActiveWindowChangedHandler(object sender, String windowHeader, IntPtr hwnd);
    public event ActiveWindowChangedHandler ActiveWindowChanged;
 
    [DllImport("user32.dll")]
    static extern IntPtr GetForegroundWindow();
    [DllImport("user32.dll")]
    static extern int GetWindowText(IntPtr hWnd, StringBuilder text, int count);

    delegate void WinEventDelegate(IntPtr hWinEventHook, uint eventType,
        IntPtr hwnd, int idObject, int idChild, uint dwEventThread,
        uint dwmsEventTime);

    const uint WINEVENT_OUTOFCONTEXT = 0;
    const uint EVENT_SYSTEM_FOREGROUND = 3;

    [DllImport("user32.dll")]
    static extern bool UnhookWinEvent(IntPtr hWinEventHook);

    [DllImport("user32.dll")]
    static extern IntPtr SetWinEventHook(uint eventMin, uint eventMax,
        IntPtr hmodWinEventProc, WinEventDelegate lpfnWinEventProc,
        uint idProcess, uint idThread, uint dwFlags);

    IntPtr m_hhook;
    private WinEventDelegate _winEventProc;

    public ActiveWindow()
    {
        _winEventProc = new WinEventDelegate(WinEventProc);
        m_hhook = SetWinEventHook(EVENT_SYSTEM_FOREGROUND,
            EVENT_SYSTEM_FOREGROUND, IntPtr.Zero, _winEventProc,
            0, 0, WINEVENT_OUTOFCONTEXT);
    }

    void WinEventProc(IntPtr hWinEventHook, uint eventType, IntPtr hwnd,
        int idObject, int idChild, uint dwEventThread, uint dwmsEventTime)
    {
        if (eventType == EVENT_SYSTEM_FOREGROUND)
        {
            if (ActiveWindowChanged != null)
                ActiveWindowChanged(this,GetActiveWindowTitle(hwnd),hwnd);
        }
    }

    private string GetActiveWindowTitle(IntPtr hwnd)
    {
        StringBuilder Buff = new StringBuilder(500);
        GetWindowText(hwnd, Buff, Buff.Capacity);
        return Buff.ToString();
    }

    ~ActiveWindow()
    {
        UnhookWinEvent(m_hhook);
    }
}