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Knowing when the user locks the PC

Posted on 2009-05-07
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Last Modified: 2013-12-17
Hi,
   As an initiative to save power in my company, I am planning to write an application which turns off the monitor when the user locks his/her PC.

   The OS is Windows XP SP2.

   I have the code for switching off the monitor.

   The user locks his/her machine by either pressing the "WindowsKey + L"  or pressing "Ctrl + Alt+ Del" and then choosing the Lock Computer option.

   Should I make a windows service? how will the service come to know whether the user has locked the machine?
   I want to code it in C#.

regards,
CuteBug
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Question by:CuteBug
5 Comments
 
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Expert Comment

by:Cebik
ID: 24325101
just enable power safe - disable monitor after period of time
;)
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Author Comment

by:CuteBug
ID: 24325446
Well we do not have access to that feature. Only the sysadmins have access.
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Accepted Solution

by:
käµfm³d   👽 earned 300 total points
ID: 24327035
You can use a global key hook to trap keys pressed within the OS. From http://blogs.msdn.com/toub/archive/2006/05/03/589423.aspx

Now obviously you can modify the code to fit your needs, but as is, you could check "message" for "LWin/RWin", store it to some private variable if set and then check for "L" to be the next key pressed.

Ctrl-Alt-Delete will be a little more difficult to capture. The method below will not work. From what I have read, you have to write something called a GINA stub to capture that--please don't ask me to explain :/ The following article talks about it though.

http://msdn.microsoft.com/en-us/library/aa375198(VS.85).aspx
http://bytes.com/groups/net/108144-capture-ctrl-alt-del   <<--- last post
//////////////////////////////////////////
// Intercept Keys Class
//////////////////////////////////////////
using System;
using System.Diagnostics;
using System.Windows.Forms;
using System.Runtime.InteropServices;
 
class InterceptKeys
{
    private const int WH_KEYBOARD_LL = 13;
    private const int WM_KEYDOWN = 0x0100;
    private const int WM_SYSKEYDOWN = 0x0104; 
    private static LowLevelKeyboardProc _proc = HookCallback;
    private static IntPtr _hookID = IntPtr.Zero;
    private static ExternalCallback callback;
 
    public delegate void ExternalCallback(string message);
 
    public static void Begin(ExternalCallback cb)
    {
        _hookID = SetHook(_proc);
        callback = cb;
    }
 
    public static void End()
    {
        UnhookWindowsHookEx(_hookID);
        _hookID = IntPtr.Zero;
    }
 
    private static IntPtr SetHook(LowLevelKeyboardProc proc)
    {
        using (Process curProcess = Process.GetCurrentProcess())
        using (ProcessModule curModule = curProcess.MainModule)
        {
            return SetWindowsHookEx(WH_KEYBOARD_LL, proc,
                GetModuleHandle(curModule.ModuleName), 0);
        }
    }
 
    private delegate IntPtr LowLevelKeyboardProc(
        int nCode, IntPtr wParam, IntPtr lParam);
 
    private static IntPtr HookCallback(
        int nCode, IntPtr wParam, IntPtr lParam)
    {
        if (nCode >= 0 && (wParam == (IntPtr)WM_KEYDOWN || wParam == (IntPtr)WM_SYSKEYDOWN))
        {
            int vkCode = Marshal.ReadInt32(lParam);
            callback.Invoke(((Keys)vkCode).ToString());
        }
        return CallNextHookEx(_hookID, nCode, wParam, lParam);
    }
 
    [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
    private static extern IntPtr SetWindowsHookEx(int idHook,
        LowLevelKeyboardProc lpfn, IntPtr hMod, uint dwThreadId);
 
    [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static extern bool UnhookWindowsHookEx(IntPtr hhk);
 
    [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
    private static extern IntPtr CallNextHookEx(IntPtr hhk, int nCode,
        IntPtr wParam, IntPtr lParam);
 
    [DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
    private static extern IntPtr GetModuleHandle(string lpModuleName);
}
 
 
//////////////////////////////////////////
// Form
//////////////////////////////////////////
using System;
using System.Windows.Forms;
 
namespace WindowsFormsApplication3
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
 
        private void Form1_Load(object sender, EventArgs e)
        {
            InterceptKeys.Begin(UpdateBox);
        }
 
        private void Form1_FormClosing(object sender, FormClosingEventArgs e)
        {
            InterceptKeys.End();
        }
 
        private void UpdateBox(string message)
        {
            this.listBox1.Items.Add(message);
        }
    }
}

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Assisted Solution

by:Mike Tomlinson
Mike Tomlinson earned 200 total points
ID: 24328106
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Author Closing Comment

by:CuteBug
ID: 31578966
Thanks a lot! Your answers have been very helpful.
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