Enumerating PowerShell object's properties throws

Question

I have this simple program using powershell. This is just a proof of concept, I'm using the same code in a larger app. The problem is that the values of some of the properties in the code below can't be read. Reading the Value property throws a GetValueInvocationException.

This actually even happens with one of Microsoft sample projects that comes with the PowerShell SDK. Why is this and is there a solution?

static void Main(string[] args)
    {
        var powerShell = System.Management.Automation.PowerShell.Create();

        var runspace = RunspaceFactory.CreateRunspace();
        runspace.Open();
        Runspace.DefaultRunspace = runspace;

        powerShell.Runspace = runspace;
        powerShell.AddScript("Get-Process");
        var results = powerShell.Invoke();

        foreach (var prop in results.First().Properties)
        {
            try
            {
                Console.WriteLine(prop.Name + " : " + prop.Value);
            }
            catch (Exception e)
            {
                Console.WriteLine(string.Format("Exception {0} on {1}", e.GetType(), prop.Name));
            }
        }

        Console.ReadKey();
    }

Roman Kuzmin · Accepted Answer · 2011-06-22 10:07:06Z

2

This is either by design (after all, it a target object property getter throws) or an issue (if this effect is not intentional in PowerShell). In both cases we cannot do much about this now. That is, we should use the try/catch approach in such vcases. One option we have is to submit the report to: https://connect.microsoft.com/PowerShell/Feedback

Try to get the target object in your C# code (it is System.Diagnostics.Process, get it via BaseObject property of a result object) and access that culprit property. It will throw, more likely, as well.

answered Jun 22, 2011 at 10:07

Roman Kuzmin

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2 Comments

LinusK Over a year ago

Yeah you're probably right. I should just ignore those properties. The thing is that I am doing this generally and don't really know in code what the BaseObject is. What I did before (and wanted to change) was using the PowerShell Job API. Then I had no such problems. But when I look at the properties returned I see that that the properties throwing exceptions in my example is not available when using the Job approach. So I guess try/catch is the way to go. Thanks :)

Roman Kuzmin Over a year ago

Yes, try/catch is what I do in my custom host when it deals with unknown objects (read, objects which property getters may throw).

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