How to call a complex COM method from PowerShell?

Question

Is it possible to call a COM method from PowerShell using named parameters? The COM object method I am working with has dozens of parameters:

object.GridData         


        

Answer 1

This problem did interest me, so I did some real digging and I have found a solution (though I have only tested on some simple cases)!

Concept

The key solution is using [System.Type]::InvokeMember which allows you to pass parameter names in one of its overloads.

Here is the basic concept.

$Object.GetType().InvokeMember($Method, [System.Reflection.BindingFlags]::InvokeMethod,
    $null,  ## Binder
    $Object,  ## Target
    ([Object[]]$Args),  ## Args
    $null,  ## Modifiers
    $null,  ## Culture
    ([String[]]$NamedParameters)  ## NamedParameters
)

Solution

Here is a reusable solution for calling methods with named parameters. This should work on any object, not just COM objects. I made a hashtable as one of the parameters so that specifying the named parameters will be more natural and hopefully less error prone. You can also call a method without parameter names if you want by using the -Argument parameter

Function Invoke-NamedParameter {
    [CmdletBinding(DefaultParameterSetName = "Named")]
    param(
        [Parameter(ParameterSetName = "Named", Position = 0, Mandatory = $true)]
        [Parameter(ParameterSetName = "Positional", Position = 0, Mandatory = $true)]
        [ValidateNotNull()]
        [System.Object]$Object
        ,
        [Parameter(ParameterSetName = "Named", Position = 1, Mandatory = $true)]
        [Parameter(ParameterSetName = "Positional", Position = 1, Mandatory = $true)]
        [ValidateNotNullOrEmpty()]
        [String]$Method
        ,
        [Parameter(ParameterSetName = "Named", Position = 2, Mandatory = $true)]
        [ValidateNotNull()]
        [Hashtable]$Parameter
        ,
        [Parameter(ParameterSetName = "Positional")]
        [Object[]]$Argument
    )

    end {  ## Just being explicit that this does not support pipelines
        if ($PSCmdlet.ParameterSetName -eq "Named") {
            ## Invoke method with parameter names
            ## Note: It is ok to use a hashtable here because the keys (parameter names) and values (args)
            ## will be output in the same order.  We don't need to worry about the order so long as
            ## all parameters have names
            $Object.GetType().InvokeMember($Method, [System.Reflection.BindingFlags]::InvokeMethod,
                $null,  ## Binder
                $Object,  ## Target
                ([Object[]]($Parameter.Values)),  ## Args
                $null,  ## Modifiers
                $null,  ## Culture
                ([String[]]($Parameter.Keys))  ## NamedParameters
            )
        } else {
            ## Invoke method without parameter names
            $Object.GetType().InvokeMember($Method, [System.Reflection.BindingFlags]::InvokeMethod,
                $null,  ## Binder
                $Object,  ## Target
                $Argument,  ## Args
                $null,  ## Modifiers
                $null,  ## Culture
                $null  ## NamedParameters
            )
        }
    }
}

Examples

Calling a method with named parameters.

$shell = New-Object -ComObject Shell.Application
Invoke-NamedParameter $Shell "Explore" @{"vDir"="$pwd"}

## the syntax for more than one would be @{"First"="foo";"Second"="bar"}

Calling a method that takes no parameters (you can also use -Argument with $null).

$shell = New-Object -ComObject Shell.Application
Invoke-NamedParameter $Shell "MinimizeAll" @{}