Start a screensaver when explorer is not the shell

Question

I'm running my own kiosk application as the shell (replacing HKLM/Software/Microsoft/Windows NT/winlogon/shell).

The application needs to be able to turn off the monitor and I was using Process.Start("scrnsave.scr") to do this. It works on my dev machine but not when the shell is replaced.

It's clearly because the UseShellExecute is set to true, but when I set it to false I can't get the screensaver to run. Using explorer.exe as the command and scrnsave.scr as the argument just causes an explorer window to open.

Is there a switch I can pass to explorer to get it to run the screensaver or is there another way to achieve the same thing?

Thanks.

Answer 1

You can start the screen saver by sending a windows message to the system.

SendMessage(HWND_BROADCAST, WM_SYSCOMMAND, SC_SCREENSAVE, 0)

You will need the following definitions

static readonly IntPtr HWND_BROADCAST = new IntPtr(0xffff);
static readonly IntPtr SC_SCREENSAVE = new IntPtr(0xf140);
const uint WM_SYSCOMMAND = 0x112;

[DllImport("User32",SetLastError=true)]
extern static int SendMessage(
  IntPtr hWnd,
  uint Msg,
  IntPtr wParam,
  IntPtr lParam);

Which you can then use as follows

SendMessage(HWND_BROADCAST, WM_SYSCOMMAND, SC_SCREENSAVE, IntPtr.Zero);