Getting a cmdlet's dynamic parameters via reflection

Question

Powershell exposes some parameters, "dynamic parameters", based on context. The MSDN page explains the mechanism pretty well, but the skinny is that to find out about these one must call GetDynamicParameters(), which returns a class containing the additional parameters. I need to get these parameters via reflection, and (here's the crux of it), in a ReflectionOnly context (that is, the types are loaded with ReflectionOnlyLoadFrom). So, no Assembly.InvokeMember("GetDynamicParameters").

Can this be done?

Answer 1

No. Reflection works against static assembly metadata. Dynamic parameters in powershell are added at runtime by the command or function itself.

Answer 2

Perhaps this helps:

1: Defintion of the dynamic parameters

#===================================================================================
# DEFINITION OF FREE FIELDS USED BY THE CUSTOMER
#-----------------------------------------------------------------------------------
# SYNTAX: @{ <FF-Name>=@(<FF-Number>,<isMandatory_CREATE>,<isMandatory_UPDATE>); }
$usedFFs = @{               
                      "defaultSMTP"=@(2,1,0); `
                      "allowedSMTP"=@(3,1,0); `
                       "secondName"=@(100,1,0); `
                            "orgID"=@(30001,1,0); `
            "allowedSubjectTypeIDs"=@(30002,1,0); `
            }

# FF-HelpMessage for input          
$usedFFs_HelpMSG = @{ 2="the default smtp domain used by the organizaiton. Sampel:'algacom.ch'"; `
                      3="comma seperated list of allowed smtp domains. Sampel:'algacom.ch,basel.algacom.ch'"; `
                      100="an additional organization name. Sampel:'algaCom AG')"; `
                      30001="an unique ID (integer) identifying the organization entry"; `
                      30002="comma seperated list of allowed subject types. Sampel:'1,2,1003,10040'"; `
            }

2: definition of function that builds the dynamic parameters

#-------------------------------------------------------------------------------------------------------        
# Build-DynParams : Used to build the dynamic input parameters based on $usedFFs / $usedFFs_HelpMSG
#-------------------------------------------------------------------------------------------------------
function Build-DynParams($type) {
    $paramDictionary = New-Object -Type System.Management.Automation.RuntimeDefinedParameterDictionary

    foreach($ffName in $usedFFs.Keys) {
        $ffID = $usedFFs.Item($ffName)[0]
        $dynAttribCol = New-Object -Type System.Collections.ObjectModel.Collection[System.Attribute]
        $dynAttrib = New-Object System.Management.Automation.ParameterAttribute
        $dynAttrib.ParameterSetName = "__AllParameterSets"
        $dynAttrib.HelpMessage = $usedFFs_HelpMSG.Item($ffID)
        switch($type) {
            "CREATE" { $dynAttrib.Mandatory = [bool]($usedFFs.Item($ffName)[1]) }
            "UPDATE" { $dynAttrib.Mandatory = [bool]($usedFFs.Item($ffName)[2]) }
        }   
        $dynAttribCol.Add($dynAttrib)   
        $dynParam = New-Object -Type System.Management.Automation.RuntimeDefinedParameter($ffName, [string], $dynAttribCol)
        $paramDictionary.Add($ffName, $dynParam)        
    }
    return $paramDictionary         
}

3. Function that makes use of the dynamic params

#-------------------------------------------------------------------------------------------------------
# aAPS-OrganizationAdd : This will add a new organization entry
#-------------------------------------------------------------------------------------------------------
Function aAPS-OrganizationAdd {
    [CmdletBinding()]
    Param(
        [Parameter(Mandatory=$true,HelpMessage="The name of the new organization")] 
        [String]$Descr,
        [Parameter(Mandatory=$false,HelpMessage="The name of the parent organization")] 
        [String]$ParentDescr=$null,
        [Parameter(Mandatory=$false,HelpMessage="The status of the new organization [1=Active|2=Inactive]")] 
        [int]$Status = 1,
        [Parameter(Mandatory=$false,HelpMessage="If you want to see the data of the deactivated object")] 
        [switch]$ShowResult
    )
    DynamicParam { Build-DynParams "CREATE" }

    Begin {}

    Process {
        # do what oyu want here
    }

    End {}
}