send display to sleep mode in c#

Question

it's a standard windows function that the display goes into sleep mode after the configured time. is it somehow possible to send the display into sleep mode immediately from a c# .net application in windows 7? i've already tried one thing i found but it didn't work for me.

[DllImport("user32.dll")]
static extern IntPtr SendMessage(IntPtr hWnd, UInt32 Msg, IntPtr wParam, IntPtr lParam);

[DllImport("user32.dll", CharSet = CharSet.Auto, ExactSpelling = true)]
public static extern IntPtr GetDesktopWindow();

private const int SC_MONITORPOWER = 0xF170;
private const UInt32 WM_SYSCOMMAND = 0x0112;
private const int MONITOR_ON = -1;
private const int MONITOR_OFF = 2;
private const int MONITOR_STANBY = 1;

public static void DisplayToSleep()
{
    var hWnd = GetDesktopWindow();
    var ret = SendMessage(hWnd , Constants.WM_SYSCOMMAND, (IntPtr)Constants.SC_MONITORPOWER, (IntPtr)Constants.MONITOR_OFF);
}

hWnd seems to have a valid value but ret is always 0.

thx, kopi_b

Darin Dimitrov · Accepted Answer · 2010-08-29T13:09:17.313

9

This works fine in a WinForms application:

public partial class Form1 : Form
{
    private int SC_MONITORPOWER = 0xF170;
    private uint WM_SYSCOMMAND = 0x0112;

    [DllImport("user32.dll")]
    static extern IntPtr SendMessage(IntPtr hWnd, uint Msg, IntPtr wParam, IntPtr lParam);

    public Form1()
    {
        InitializeComponent();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        SendMessage(this.Handle, WM_SYSCOMMAND, (IntPtr)SC_MONITORPOWER, (IntPtr)2);
    }
}

The problem seems to come from the GetDesktopWindow function.

edited Aug 29 '10 at 13:09

answered Aug 29 '10 at 11:12

Darin Dimitrov

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+1, agreed. Fix your SendMessage() declaration, it won't work on a 64-bit operating system. – Hans Passant Aug 29 '10 at 12:42
@Hans, good point, it actually worked on my Windows 7 x64 bit but it could break depending on the address. I fixed my declaration. – Darin Dimitrov Aug 29 '10 at 12:54
@Hans, how about now? Is it correct casting an `int` to `IntPtr` as I did? – Darin Dimitrov Aug 29 '10 at 13:09

score 5 · Answer 2 · answered Aug 29 '10 at 11:21

You need to use HWND_BROADCAST instead of the desktop window handle to ensure that the monitor powers off:

private const int HWND_BROADCAST = 0xFFFF;

var ret = SendMessage((IntPtr)HWND_BROADCAST, WM_SYSCOMMAND, (IntPtr)SC_MONITORPOWER, (IntPtr)MONITOR_OFF);

score 0 · Answer 3 · answered Aug 29 '10 at 11:19

I have Visual Studio 2010 and Windows 7 and created a Windows Form Application with a 'Sleep' and 'Hibernate' button. The following worked for me:

private void Sleep_Click(object sender, EventArgs e)
{
    bool retVal = Application.SetSuspendState(PowerState.Suspend, false, false);

    if (retVal == false)
        MessageBox.Show("Could not suspend the system.");
}

private void Hibernate_Click(object sender, EventArgs e)
{
    bool retVal = Application.SetSuspendState(PowerState.Hibernate, false, false);

    if (retVal == false)
        MessageBox.Show("Could not hybernate the system.");
}

I found this here

i guess that will work, yes. but i don't want to suspend or hibernate the whole system, just the monitor should go to sleep. — kopi_b, Aug 29 '10 at 14:09

send display to sleep mode in c#

3 Answers3