Using dynamic parameters value in PowerShell

Question

I am trying to use a dynamic parameter in PowerShell, but the value for the parameter doesn't seem to exist after I have run through my script.

[CmdletBinding()]
Param (
    [Parameter(
         Mandatory=$true,
         Position=0,
         HelpMessage = "The entity ID for the Version"
    )]
    [string]$TPVersionID,

    [Parameter(
         Mandatory=$true,
         Position=1,
         HelpMessage = ""
    )]
    [string]$VersionNumber,

    [Parameter(
         Mandatory=$true,
         Position=2,
         HelpMessage = "This is a boolean value; enter any value to make it True, leave it blank to make it False."
    )]
    [bool]$PullVersionDoc
)


function Get-VersionParam{
    [CmdletBinding()]
    Param ([string]$TPVersionID, [string]$VersionNumber, [bool]$PullVersionDoc?)
    DynamicParam {
        if ($PullVersionDoc) {
            write-host("HEY!")

            $attributes = new-object System.Management.Automation.ParameterAttribute
            $attributes.Position = 3
            $attributes.Mandatory = $true
            $attributeCollection = new-object `
                -Type System.Collections.ObjectModel.Collection[System.Attribute]
            $attributeCollection.Add($attributes)

            $dynParam1 = new-object `
                -Type System.Management.Automation.RuntimeDefinedParameter('VersionDocumentID', [Int32], $attributeCollection)

            $paramDictionary = new-object `
                -Type System.Management.Automation.RuntimeDefinedParameterDictionary
            $paramDictionary.Add('VersionDocumentID', $dynParam1)
            return $paramDictionary
        }
    }
}


Get-VersionParam


#Write-Host "Dynamic Parameter PullVersionDoc? = " $PullVersionDoc
Write-Host $PSBoundParameters

I want the script to ask for a [VersionDocumentID] if the boolean value for [PullVersionDoc] is TRUE to use later on in the script, but when I write out the [$PSBoundParameters] the parameter doesn't exist. How did I get the value so that I can use it?

There's also no point in using a [bool] parameter. Use [switch] instead. This way you add the param name to make Switch True or leave it off and it will evaluate to False. Also, you access $PSBoundParameters[$ParameterName] in the Begin block and work on items within the Process block. — user4317867
– user4317867, Commented Feb 19, 2017 at 1:09
I'm not sure I understand. The VersionDocumentID parameter will only exist inside the function, unless you add something like $script:VersionDocumentID = $VersionDocumentID to your function body (or outputs the value and store it like @4c74356b41 showed) . Your function doesn't do anything except ask for values it never uses. — Frode F.
– Frode F., Commented Feb 19, 2017 at 12:54
I agree with @FrodeF. which prompted me to post my complete Dynamic Param example script in the hopes it will assist the OP. — user4317867
– user4317867, Commented Feb 19, 2017 at 20:46

Peter Mortensen · Accepted Answer · 2019-02-23 12:00:59Z

Here's how I tried using dynamic parameters to get Configuration Manager logs.

Credit goes to the blog post here.

Usage: Get-CCMLogs -ComputerNames -Remote -RemoteLogName <Tab to complete lognames>

Local usage: Get-CCMLogs -ComputerNames -LocalLogName <Tab to complete lognames>

The dynamic parameter will return a remote log name if the switch -Remote is entered or return a local log name if the switch -Remote is not entered.

Function Get-CCMLogs {

    [CmdletBinding()]

    Param(
        [Parameter(Mandatory=$false,
            ValueFromPipeline=$true,
            ValueFromPipelineByPropertyName=$true,
            HelpMessage="Give me a list of computer names!")]
        [Alias('Hostname','cn')]
        [string[]]$ComputerNames = $env:COMPUTERNAME,

        [switch]$Remote
    )

    DynamicParam{

        If ($Remote) {

            $ParameterName = 'RemoteLogName'

            $RunTimeDictionary = New-Object System.Management.Automation.RuntimeDefinedParameterDictionary

            $AttributeCollection = New-Object System.Collections.ObjectModel.Collection[System.Attribute]

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

            $AttributeCollection.Add($ParamAttribute)

            $ValidateItems = Get-ChildItem -Path "\\$ComputerNames\C$\Windows\CCM\Logs" | Where {$_ -notmatch '\d+'} | Select -ExpandProperty FullName
            $ValidateSetAttribute = New-Object System.Management.Automation.ValidateSetAttribute($ValidateItems)

            $AttributeCollection.Add($ValidateSetAttribute)

            $RunTimeParam = New-Object System.Management.Automation.RuntimeDefinedParameter($ParameterName, [string], $AttributeCollection)

            $RunTimeDictionary.Add($ParameterName, $RunTimeParam)

            Return $RunTimeDictionary
        }
        else {
            $ParameterName = 'LocalLogName'

            $RunTimeDictionary = New-Object System.Management.Automation.RuntimeDefinedParameterDictionary

            $AttributeCollection = New-Object System.Collections.ObjectModel.Collection[System.Attribute]

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

            $AttributeCollection.Add($ParamAttribute)

            $ValidateItems = Get-ChildItem -Path C:\Windows\CCM\Logs | Select -ExpandProperty FullName | Where {$_ -notmatch '\d+'}
            $ValidateSetAttribute = New-Object System.Management.Automation.ValidateSetAttribute($ValidateItems)

            $AttributeCollection.Add($ValidateSetAttribute)

            $RunTimeParam = New-Object System.Management.Automation.RuntimeDefinedParameter($ParameterName, [string], $AttributeCollection)

            $RunTimeDictionary.Add($ParameterName, $RunTimeParam)

            Return $RunTimeDictionary
        }
    }

    Begin{
        $LogName = $PSBoundParameters[$ParameterName]
    }

    Process{
        cmtrace.exe $LogName
    }
}

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