Cannot Generate ParameterSetMetadata While Programmatically Creating A Parameter Block

Question

I'm trying to programmatically create a parameter block for a function ( along the lines of this blog post ).

I'm starting with a CommandMetadata object (from an existing function). I can create the ParameterMetadata object and set things like the ParameterType, the name, as well as some attributes.

The problem I'm running into is that when I use the GetParamBlock method of the ProxyCommand class, none of my attributes that I set in the Attributes collection of the ParameterMetadata are generated.

The problem this causes is that when the GetParamBlock is called, the new parameter is not annotated with the appropriate Parameter attribute.

Example:

function test 
{
    [CmdletBinding()]
    param (
    [Parameter()]
    $InitialParameter)

    Write-Host "I don't matter."
}

$MetaData = New-Object System.Management.Automation.CommandMetaData (get-command test)

$NewParameter = New-Object System.Management.Automation.ParameterMetadata 'NewParameter'

$NewParameter.ParameterType = [string[]]

$Attribute = New-Object System.Management.Automation.ParameterAttribute 
$Attribute.Position = 1
$Attribute.Mandatory = $true
$Attribute.ValueFromPipeline = $true

$NewParameter.Attributes.Add($Attribute)
$MetaData.Parameters.Add('NewParameter', $NewParameter)


[System.Management.Automation.ProxyCommand]::GetParamBlock($MetaData) 

Answer 1

Hi Steven,

The reason it does not show up is because your NewParameter needs to belong to at least one parameter set. In this case, it should be a member of the special parameterset, "__AllParameterSets."

You can verify this by copying the ParameterSetMetadata instance from InitialParameter. Unfortuntely I can't see immediately how to get this ParameterSetMetadata if you don't have any parameters to grab it from. Copying it from the other parameter makes it appear in the output, but it's the metadata from InitialParameter, so this is not the solution, only the reason why it doesn't work (yet.) I'll update this post when I figure it out.

-Oisin

Answer 2

function test 
{
    [CmdletBinding()]
    param (
    [Parameter()]
    $InitialParameter)

    Write-Host "I don't matter."
}

$MetaData = New-Object System.Management.Automation.CommandMetaData (get-command test)

$NewParameter = New-Object System.Management.Automation.ParameterMetadata 'NewParameter'

$NewParameter.ParameterType = [string[]]

$Attribute = New-Object System.Management.Automation.ParameterAttribute 
$Attribute.Position = 1
$Attribute.Mandatory = $true
$Attribute.ValueFromPipeline = $true

$NewParameter.Attributes.Add($Attribute)
$MetaData.Parameters.Add('NewParameter', $NewParameter)

$ParameterSetMetadata = "System.Management.Automation.ParameterSetMetadata"
$ParameterSetInfo = new-object psobject -Property @{ 
    Position=[Int]::MinValue
    Flags=3
    HelpMessage="Please Enter a Value"
} | ForEach { 
    $_.PSTypeNames.Add("Deserialized.$ParameterSetMetadata")
    write-Output $_ 
}

$converter = new-object  Microsoft.PowerShell.DeserializingTypeConverter
$ConvertedSet = $converter.ConvertFrom($ParameterSetInfo,$ParameterSetMetadata, $null, $true)

$NewParameter.ParameterSets.Add('__AllParameterSets', $ConvertedSet )

[System.Management.Automation.ProxyCommand]::GetParamBlock($MetaData)