为PowerShell的Get-ChildItem动态创建的参数参数

function Get-FilteredChildItem {
    [CmdletBinding()]
    Param (
        [Parameter(Position = 0, Mandatory = $true, ValueFromPipeline = $true, ValueFromPipelineByPropertyName = $true)]
        [Alias("FullName")]
        [string]$Path
    )

    DynamicParam {
        $attributes = Get-ChildItem -Path $Path | Select-Object -Property Attributes -Unique
        $attributeNames = $attributes | ForEach-Object { $_.Attributes.ToString() }

        $paramDictionary = New-Object -Type System.Management.Automation.RuntimeDefinedParameterDictionary

        $attributeParam = New-Object -Type System.Management.Automation.ParameterAttribute
        $attributeParam.ParameterSetName = "ByAttribute"
        $attributeParam.Mandatory = $false
        $attributeParam.Position = 1
        $attributeParam.HelpMessage = "Filter by attribute."
        $attributeParam.ValidValues = $attributeNames

        $paramDictionary.Add("Attribute", $attributeParam)

        return $paramDictionary
    }

    Process {
        $attributeValue = $PSBoundParameters["Attribute"]

        if ($attributeValue) {
            Get-ChildItem -Path $Path | Where-Object { $_.Attributes.ToString() -eq $attributeValue }
        } else {
            Get-ChildItem -Path $Path
        }
    }
}

Get-FilteredChildItem -Path "C:\Path\To\Folder" -Attribute "Directory"