How to execute PowerShell Net MessageBox in cmd/batch - powershell

Question

I have a batch file with lot of stuff. I there is one Alert Window with info for user.
On Windows Pro I'm using Msg command for it and it works fine.
On Windows Home there is no Msg, so I got the idea to use PowerShell instead:
[System.Windows.Forms.MessageBox]::Show("my text")
which works fine in PowerShell.
-However, when I try to use it in batch or execute it directly in Cmd, I only get the text:
C:\Windows\System32>powershell {[System.Windows.Forms.MessageBox]::Show("\""my text"\"")}
[System.Windows.Forms.MessageBox]::Show("my text")
Or I get errors:
C:\Windows\System32>powershell -command [System.Windows.Forms.MessageBox]::Show("my text")
At line:1 char:41
+ [System.Windows.Forms.MessageBox]::Show(my text)
+ ~
Missing ')' in method call.
At line:1 char:41
+ [System.Windows.Forms.MessageBox]::Show(my text)
+ ~~
Unexpected token 'my' in expression or statement.
At line:1 char:48
+ [System.Windows.Forms.MessageBox]::Show(my text)
+ ~
Unexpected token ')' in expression or statement.
+ CategoryInfo : ParserError: (:) [], ParentContainsErrorRecordException
+ FullyQualifiedErrorId : MissingEndParenthesisInMethodCall
or
C:\Windows\System32>powershell -command "& {[System.Windows.Forms.MessageBox]::Show('my text')}"
Unable to find type [System.Windows.Forms.MessageBox].
At line:1 char:4
+ & {[System.Windows.Forms.MessageBox]::Show('my text')}
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidOperation: (System.Windows.Forms.MessageBox:TypeName) [],
RuntimeException
+ FullyQualifiedErrorId : TypeNotFound
What should I do to get it to work?
(without rewriting the whole script to PowerShell, that is)

Answer 1

As TheMadTechnician stated, you may need to load it first.
This is effectively the same answer as theirs just over a couple of lines:
#Echo Off
PowerShell -Command^
"[Reflection.Assembly]::LoadWithPartialName('System.Windows.Forms')|Out-Null;"^
"[System.Windows.Forms.MessageBox]::Show(\"my text\")"
Pause
…and whilst double quotes around my text is not necessary, I've used them to show you the escapes.

Answer 2

You need to load the type before you can invoke it. You can do this:
powershell -command "[reflection.assembly]::LoadWithPartialName('System.Windows.Forms')|out-null;[windows.forms.messagebox]::Show('my message')"