Msgbox in PowerShell script run from task scheduler not working - powershell

Question

I have a PowerShell script that creates a schedule task to launch the script. The idea is there are some task in the script that requires reboot. At the end of the PowerShell a message box should prompt the user to let the user knows that all the tasks are completed. What am i doing wrong?
Add-Type -AssemblyName PresentationFramework
TaskName = "Run Agents Install Script"
$TaskDescription = "Run Agents Install Script at logon"
$Action = New-ScheduledTaskAction -Execute 'Powershell.exe' `
-Argument "-executionpolicy remotesigned -File $PSScriptRoot\AgentInstall.ps1"
$Trigger = New-ScheduledTaskTrigger -AtLogOn
Register-ScheduledTask -Action $Action -Trigger $Trigger -TaskName $TaskName -Description $TaskDescription -User "System"
$MsgBoxInput = [System.Windows.MessageBox]::Show('Installation completed successfully.','Agent Install','OK')
Switch ($MsgBoxInput) {
'OK'
{
$MsgBoxInput = [System.Windows.MessageBox]::Show('WARNING! Please install Imprivata agent manually if applicable.','Agent Install','OK')
}
}

Answer 1

One option is to use the Terminal Services API to send a message to the console. Unfortunately, it is native API, so you need to use .NET interop to call it, but in this case it isn't too tricky:
$typeDefinition = #"
using System;
using System.Runtime.InteropServices;
public class WTSMessage {
[DllImport("wtsapi32.dll", SetLastError = true)]
public static extern bool WTSSendMessage(
IntPtr hServer,
[MarshalAs(UnmanagedType.I4)] int SessionId,
String pTitle,
[MarshalAs(UnmanagedType.U4)] int TitleLength,
String pMessage,
[MarshalAs(UnmanagedType.U4)] int MessageLength,
[MarshalAs(UnmanagedType.U4)] int Style,
[MarshalAs(UnmanagedType.U4)] int Timeout,
[MarshalAs(UnmanagedType.U4)] out int pResponse,
bool bWait
);
static int response = 0;
public static int SendMessage(int SessionID, String Title, String Message, int Timeout, int MessageBoxType) {
WTSSendMessage(IntPtr.Zero, SessionID, Title, Title.Length, Message, Message.Length, MessageBoxType, Timeout, out response, true);
return response;
}
}
"#
Add-Type -TypeDefinition $typeDefinition
[WTSMessage]::SendMessage(1, "Message Title", "Message body", 30, 36)
This is essentially a thin wrapper to the WTSSendMessage function.
You will need to get the SessionID via some tool like query. This script might help with that: Get-UserSession.
The TimeOut value here is 30, which means the pop-up will wait 30 seconds before returning with a value of '32000'. Set to '0' to wait forever.
The MessageBoxType is a combination of the values for uType here: MessageBox Function. So the '36' in the example is a combination of the values for 'MB_YESNO' and 'MB_ICONQUESTION', so will show a message with a question mark icon and 'yes'/'no' buttons. Note that the documentation gives the values in hexadecimal, so you'll need to convert them.
I tested this as a scheduled task running as an admin and it was able to show a message on the desktop of a different logged on user. hope it helps.