Question

Ok this one is puzzling me. I have an abstract base class named Testbase and it has an abstract function called RunTest. In a folder I have a collection of classes that inherit this abstract class. In a test controller I call the following code to create a list of instances of these Test Classes.

        String ns = "HCTCommon.Tests";
        var query = from t in Assembly.GetExecutingAssembly().GetTypes()
                    where t.Namespace == ns
                    select t;

        foreach (object t in query)
        {
            TestBase test = (TestBase)Activator.CreateInstance(t as Type);
            testList.Add(test);
        }

in one of the classes RunTest function I was cleaning up code and decided to use lambda expressions and tried various versions.

pullservice = ServiceController.GetServices().FirstOrDefault(s => s.ServiceName == serviceName);

and

pullservice = ServiceController.GetServices().Where(s => s.DisplayName.Equals("Pull Service")).ToList()[0];

are the ones I remember but anytime i use the lambda’s rather than running through some convoluted foreach loop i get an invalidcastexception on the line of code

TestBase test = (TestBase)Activator.CreateInstance(t as Type);

Exception:

Unable to cast object of type '<>c__DisplayClass4' to type 'HCTCommon.TestBase'.

Stack Trace:

   at HCTCommon.TestController.populateTestList()
   at HCTCommon.TestController..ctor(RegistryKey Key)
   at HealthCheck.HealthCheckForm.InitializeTestPanels() in C:\Users\bkoch.ESI911\documents\visual studio 2010\Projects\HCTCommon\HealthCheck\HealthCheckForm.cs:line 55
   at HealthCheck.HealthCheckForm..ctor() in C:\Users\bkoch.ESI911\documents\visual studio 2010\Projects\HCTCommon\HealthCheck\HealthCheckForm.cs:line 26
   at HealthCheck.Program.registrycheck() in C:\Users\bkoch.ESI911\documents\visual studio 2010\Projects\HCTCommon\HealthCheck\Program.cs:line 63
   at HealthCheck.Program.Main() in C:\Users\bkoch.ESI911\documents\visual studio 2010\Projects\HCTCommon\HealthCheck\Program.cs:line 34
   at System.AppDomain._nExecuteAssembly(Assembly assembly, String[] args)
   at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
   at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
   at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.ThreadHelper.ThreadStart()

Answer 1

The lambda expression generates an anonymous closure class to hold local variables.
Your code is incorrectly picking up this class.

You should add

where typeof(TestBase).IsAssignableFrom(t)