"You cannot call a method on a null-valued expression" when passing parameters to powershell

Question

I'm trying to parse some parameters to a script I'm running in powershell. But I'm getting errors while executing the script saying they are empty.

Im starting the process like this:

string input1 = "Powershell.exe -File " + Config.Directory + "/ICS.ps1" + " -toggle '" + toggle + "' -par1 '" +
                par1 + "' -par2 '" + par2 + "' -connectionInterface '" + connectionInterface + "'";

//(for readability) input1 will look something like this:
//Powershell.exe -File map/to/ICS.ps1 -toggle 'EnableSharing' -par1 '0' -par2 '1' -connectionInterface 'Ethernet'

string[] output = CmdProcess.Exec(input1);

CmdProcess.Exec is a method i created to quickly run a cmd process. it works like this

public static string[] Exec(params string[] parameters)
    {
        Process cmd = new Process
        {
            StartInfo =
            {
                UseShellExecute = false,
                Verb = "runas",
                FileName = @"cmd.exe",
                RedirectStandardInput = true,
                RedirectStandardOutput = true,
                CreateNoWindow = true,
            }
        };
        cmd.Start();

        foreach (string parameter in parameters)
        {
            cmd.StandardInput.WriteLine(parameter);
        }
        cmd.StandardInput.WriteLine("exit");
        return Regex.Split(cmd.StandardOutput.ReadToEnd(), "\r\n");
    }

the reason i use cmd to execute powershell is because i tried it with a powershell instance* but that crashed for an unknown reason on really fast computers (while it runs normally if you run it manually). *System.Management.Automation.Powershell

in the script i wrote this: (At the beginning of the script)

Param( [string]$toggle, [string]$par1, [string]$par2, [string]$connectionInterface )

But it gives an error the params are null :

You cannot call a method on a null-valued expression.
At C:\Users\Jeremy\AppData\Roaming\HotspotLauncher\ICS.ps1:10 char:1
+ $config.$toggle($par1)
+ ~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo          : InvalidOperation: (:) [], RuntimeException
+ FullyQualifiedErrorId : InvokeMethodOnNull

I get error's like this with all the params. not just $toggle or $par1.

---

I tried running Powershell.exe and -File ..... seperatly but that caused my thread to hang.

---

Also I'm 100% sure toggle, par1 and the rest (In the C# code) arent null themselves

---

I also tried adding [CmdletBinding()] before the params in the script but that did nothing :

[CmdletBinding()]Param( [string]$toggle, [string]$par1, [string]$par2, [string]$connectionInterface )

---

Here is the powershell script:

[CmdletBinding()]Param( [string]$toggle, [string]$par1, [string]$par2, [string]$connectionInterface )

regsvr32 hnetcfg.dll /s
$m = New-Object -ComObject HNetCfg.HNetShare
$m.EnumEveryConnection |% { $m.NetConnectionProps.Invoke($_) }
$c = $m.EnumEveryConnection |? { $m.NetConnectionProps.Invoke($_).Name -eq $connectionInterface }
$config = $m.INetSharingConfigurationForINetConnection.Invoke($c)
Write-Output $config.SharingEnabled
Write-Output $config.SharingConnectionType
$config.$toggle($par1)

$m2 = New-Object -ComObject HNetCfg.HNetShare
$m2.EnumEveryConnection |% { $m2.NetConnectionProps.Invoke($_) }
$c2 = $m2.EnumEveryConnection |? { $m2.NetConnectionProps.Invoke($_).DeviceName -Match 'Microsoft Hosted Network Virtual Adapter' }
$config2 = $m2.INetSharingConfigurationForINetConnection.Invoke($c2)
Write-Output $config2.SharingEnabled
Write-Output $config2.SharingConnectionType
$config2.$toggle($par2)

This script enables/disables Internet sharing for the $connectionInterface which could be something like Ethernet or Wifi, and set it to public ($par1) / or nothing if it has to be disabled. and does the same for microsoft hostednetwork and set it to private ($par2).

Answer 1

Don't fork a new process with powershell.exe - use the API instead:

using System.Collections.ObjectModel;
using System.IO;
using System.Management.Automation;
//...

using(PowerShell ps = PowerShell.Create())
{
    ps.AddScript(Path.Combine(Config.Directory, "ICS.ps1"))
        .AddParameter("toggle", toggle)
        .AddParameter("par1", par1)
        .AddParameter("par2", par2)
        .AddParameter("connectionInterface", connectionInterface);
    Collection<PSObject> results = ps.Invoke();
}

Remember to add a reference to the System.Management.Automation.dll assembly to your project