Using default values assigned to parameters within a dynamic parameter

PowerShell Help
1

I am working on a function with a normal string parameter, with a default values assigned, and 1 dynamic parameter. My goal is for the dynamic parameter to use the string value in the first parameter. The code works if I define the -Path parameter on the commandline, but it doesn’t seem to work with the default value. I have checked the $PSBoundParameters variable and it is empty when I call it in the dynamic parameter block. Does anyone have any advice for this? I want to provide a default location for my function, with the flexibility for the user to define their own path if desired. Thanks for any advice!

function Test-Function
{
    [CmdletBinding()]
    Param
    (
        # Param1 help description
        [Parameter(Mandatory=$true,
                   ValueFromPipelineByPropertyName=$true,
                   Position=0)]
        [string]$Path = 'C:\Temp\SubFolder1'
    )
    DynamicParam {
            # Set the dynamic parameters' name
            $ParameterName = 'FileName'
            
            # Create the dictionary 
            $RuntimeParameterDictionary = New-Object System.Management.Automation.RuntimeDefinedParameterDictionary

            # Create the collection of attributes
            $AttributeCollection = New-Object System.Collections.ObjectModel.Collection[System.Attribute]
            
            # Create and set the parameters' attributes
            $ParameterAttribute = New-Object System.Management.Automation.ParameterAttribute
            $ParameterAttribute.Mandatory = $true
            $ParameterAttribute.Position = 1

            # Add the attributes to the attributes collection
            $AttributeCollection.Add($ParameterAttribute)

            # Generate and set the ValidateSet 
            $arrSet = Get-ChildItem -Path $Path -File | select -ExpandProperty Name
            $ValidateSetAttribute = New-Object System.Management.Automation.ValidateSetAttribute($arrSet)

            # Add the ValidateSet to the attributes collection
            $AttributeCollection.Add($ValidateSetAttribute)

            # Create and return the dynamic parameter
            $RuntimeParameter = New-Object System.Management.Automation.RuntimeDefinedParameter($ParameterName, [string], $AttributeCollection)
            $RuntimeParameterDictionary.Add($ParameterName, $RuntimeParameter)
            return $RuntimeParameterDictionary
    }

    Begin 
    {
      # Bind the parameter to a friendly variable
      $FileName = $PsBoundParameters[$ParameterName]
    }
    Process
    {
      $FileName
    }
    End
    {
    }
}
2

From my experience, Parameter values wont be available in DynamicParam block. But you can check whether the parameter is bound or not with $PSBoundParameters.
Make the $Path parameter to validate for NotNull and EmptyString and check if the Parameter $File is bound or not for asking FileName Dynamically.

3

kvprasoon - Thanks for the response, as mentioned above I checked $PSBoundParameters before posting. I added the [ValidateNotNullOrEmpty()] decoration and checked $PSBoundParameters again and no go. This is something I have been playing with off and on for some time now and haven’t been able to resolve which is why I finally broke down and posted here. I think the $PSDefaultParameterValues is going the be the solution I will use to achieve my goal. Unless anyone else has a better idea. Thanks again for your time!

4
checked $PSBoundParameters again and no go

As you are aware, [ValidateNotNullOrEmpty()] is added just to make sure null or empty string is not passed to $Path parameter. with this $PSBoundParameters.Path will not get any value, but you can check whether $PSBoundParameters.ContainsKey(‘Path’) is true or false. If it is true then you don’t need to ask for $FilePath else, ask for it.