[RESOLVED] trying to turn off monitor using sendmessage

[Lord Orwell]

this code should work, but i am not 100% sure i hav the sendmessage declared right. Can someone help me debug this?

It's a console program and if you pass it the parameter "off" it is supposed to turn the monitor off. It doesn't.

Module Module1
    Declare Function SendMessage Lib "user32" Alias "SendMessageA" _
    (ByVal hwnd As Long, ByVal wMsg As Long, _
     ByVal wParam As Long, ByVal lParam As Long) As Long
    Const HWND_BROADCAST As Integer = &HFFFF
    Const SC_MONITORPOWER As Integer = &HF170
    Const WM_SYSCOMMAND As Short = &H112S
 
    Sub Main()
        Dim instr As String = Command()
        Select Case Command().ToLower
            'Make sure it matches - and look at the commandline switch 
            Case "off"
                TurnOff()
            Case "on"
                TurnOn()
        End Select
    End Sub
 
    Sub TurnOff()
        MsgBox("turning off")
 
        SendMessage(HWND_BROADCAST, WM_SYSCOMMAND, SC_MONITORPOWER, 2)
    End Sub
 
    Sub TurnOn()
        SendMessage(HWND_BROADCAST, WM_SYSCOMMAND, SC_MONITORPOWER, -1)
    End Sub
 
 
End Module

If someone has a better solution for what i need it for, i am all ears. I am writing a custom program that launches with the remote power button on my media center remote. It is to turn the monitor off and on.

Advanced planned functionality includes muting the sound at the same time.

[chris128]

If your sure its just the SendMessage API that is the problem then you should try posting this in the API section instead..

[dee-u]

I believe this should be it.

Private Declare Function SendMessage Lib "user32.dll" Alias "SendMessageA" _
   (ByVal hWnd As IntPtr, ByVal Msg As Integer, ByVal wParam As Integer, _
    ByVal lParam As Integer) As Integer

For VB6.0 it was Long but Long in VB6.0 is Integer in .Net.

[chris128]

I just had a quick go and got this code working in a winform app:

Const SC_MONITORPOWER As Integer = 61808
    Const WM_SYSCOMMAND As Integer = 274
    Const MONITOR_OFF As Integer = 2
 
    Partial Public Class API
        <System.Runtime.InteropServices.DllImportAttribute("user32.dll", EntryPoint:="SendMessage")> _
        Public Shared Function SendMessage(ByVal hWnd As IntPtr, ByVal Msg As UInteger, ByVal wParam As IntPtr, ByVal lParam As IntPtr) As Integer
        End Function
    End Class
 
 
    Private Sub Offbtn_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Offbtn.Click
        API.SendMessage(Me.Handle, WM_SYSCOMMAND, SC_MONITORPOWER, MONITOR_STANDBY)
    End Sub

Turns the monitor off as soon as Offbtn is clicked

[Lord Orwell]

I just had a quick go and got this code working in a winform app:

Const SC_MONITORPOWER As Integer = 61808
    Const WM_SYSCOMMAND As Integer = 274
    Const MONITOR_OFF As Integer = 2
 
    Partial Public Class API
        <System.Runtime.InteropServices.DllImportAttribute("user32.dll", EntryPoint:="SendMessage")> _
        Public Shared Function SendMessage(ByVal hWnd As IntPtr, ByVal Msg As UInteger, ByVal wParam As IntPtr, ByVal lParam As IntPtr) As Integer
        End Function
    End Class
 
 
    Private Sub Offbtn_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Offbtn.Click
        API.SendMessage(Me.Handle, WM_SYSCOMMAND, SC_MONITORPOWER, MONITOR_STANDBY)
    End Sub

Turns the monitor off as soon as Offbtn is clicked

you didn't declare the correct constant, but for whatever reason this isn't working on my system. It is working... My screen goes off, but it immediately turns on again. I was however able to get it to work by changing the handle to the broadcast one. This is against convention but it actually functions, whereas the "make a window and send the message to it" doesn't. Rep++ for you.

Here's my finished code:

Module Module1
    Const SC_MONITORPOWER As Integer = 61808
    Const WM_SYSCOMMAND As Integer = 274
    Const MONITOR_OFF As Integer = 2
    Partial Public Class API
        <System.Runtime.InteropServices.DllImportAttribute("user32.dll", EntryPoint:="SendMessage")> _
        Public Shared Function SendMessage(ByVal hWnd As IntPtr, ByVal Msg As UInteger, ByVal wParam As IntPtr, ByVal lParam As IntPtr) As Integer
        End Function
    End Class
    Sub main()
        API.SendMessage(&HFFFF, WM_SYSCOMMAND, SC_MONITORPOWER, MONITOR_OFF)
    End Sub
End Module

i was going to make it a toggle thing, but simply pressing any other remote button already wakes the monitor up, and that's good enough for me.

[dee-u]

Your current code should work if you will implement it the suggested modification I specified in post #3. I tried the following and it worked.

Public Class Form1

    Private Declare Function SendMessage Lib "user32.dll" Alias "SendMessageA" _
       (ByVal hWnd As IntPtr, ByVal Msg As Integer, ByVal wParam As Integer, _
        ByVal lParam As Integer) As Integer

    Const HWND_BROADCAST As Integer = &HFFFF
    Const SC_MONITORPOWER As Integer = &HF170
    Const WM_SYSCOMMAND As Short = &H112S

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        SendMessage(HWND_BROADCAST, WM_SYSCOMMAND, SC_MONITORPOWER, 2)
    End Sub
End Class

[mythoughts]

Hi, if you did get this working, do you have an app or exe file. It would be great if you could share with me. Thanks.

I just had a quick go and got this code working in a winform app:

Turns the monitor off as soon as Offbtn is clicked