Launching Screen Saver

[brjames32]

Hi people

I am trying to allow the user to launch the Windows Screen Saver by clicking on a button. I have the following code:

Option Explicit On

      
Public Class Form1
    Private 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 WM_SYSCOMMAND = &H112&
    Const SC_SCREENSAVE = &HF140&

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        SendMessage(Me.hwnd, WM_SYSCOMMAND, SC_SCREENSAVE, 0&)
    End Sub
End Class

But get the error:

Error 1 'hwnd' is not a member of 'LaunchScreensaverTest.Form1'.

any ideas why?

Thanks

[HanneSThEGreaT]

We meet again

Your SendMessage API implementation as you have it currently, is applicable only to VB 6. hwnd, is also still VB6.

In .NET the SendMessage API looks a bit different, and there is no hwnd property in .NET. .NET makes use of Handle, and to make it compatible with the new SendMessage API it has to be converted to Int32.

This is new SendMessage for .NET :

    <DllImport("user32.dll")> _
Private Shared Function SendMessage(ByVal hwnd As Int32, ByVal wMsg As Int32, ByVal wParam As Int32, ByVal lParam As Int32) As Int32
    End Function 'API used to start the default screensaver

The System.Runtime.InterOpServices namespace should also be imported.

With this implementation, you can start the screensaver like :

        Dim ScreenResult As Int32 'Returned Result For SendMessage API

        ScreenResult = SendMessage(Me.Handle.ToInt32, WM_SYSCOMMAND, SC_SCREENSAVE, 0) 'Start Current System Screen Saver

For example.

Your code should now look like this :

Imports System.Runtime.InteropServices 'For APIs

Public Class Form1

    <DllImport("user32.dll")> _
Private Shared Function SendMessage(ByVal hwnd As Int32, ByVal wMsg As Int32, ByVal wParam As Int32, ByVal lParam As Int32) As Int32
    End Function 'API used to start the default screensaver

    Private Const WM_SYSCOMMAND As Integer = &H112 'To send a "Windows" message
    Private Const SC_SCREENSAVE As Integer = &HF140 'Constant for the Screensaver


    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim ScreenResult As Int32 'Returned Result For SendMessage API

        ScreenResult = SendMessage(Me.Handle.ToInt32, WM_SYSCOMMAND, SC_SCREENSAVE, 0) 'Start Current System Screen Saver

    End Sub
End Class

Voila!

I'm also attaching one of my projects here, that lists all screensavers, checks for system themes, wallpapers etc.

This is part of this article I wrote :
Customising Your Desktop with Visual Basic.NET 2005

Have fun!

PS, I'd also recommend you to get the latest api viewer specific to .NET :
APi Viewer 2004

And read this article about the API changes in .NET from VB 6 :
Discovering the API Using Visual Basic 6 and Visual Basic .NET

[brjames32]

Hi Hannes

Thanks for the great info as usual It works a treat!

It was a mistake on my part. I took the code form an old VB6 prog I wrote years ago and forgot I couldn't just copy and paste Doh!!

Have agood day!

[HanneSThEGreaT]

That's good news!

Good job!