C# - How to access a generic typed property

My challenge for today was to get the value of generic typed properties from a generic type. Here is the code that worked.

pendingRequest is a generic-typed instance of RequestResponseAsyncResult where the Request and Response properties are generic.

First we have to get the generic type definition:

Type requestType = pendingRequest.GetType().GetGenericTypeDefinition();

Next we get the generic type arguments:

Type[] typeArgs = requestType.GetGenericArguments();

Then we create a generic base type from our generic type:

Type genericType = typeof(RequestResponseAsyncResult<,>);

The next step is to created a generic type according to the type arguments:

Type constructed = genericType.MakeGenericType(typeArgs);

Now we are able to get the property information:

PropertyInfo pireq = pendingRequest.GetType().GetProperty("Request");
PropertyInfo piresp = pendingRequest.GetType().GetProperty("Response");

Finally we can get our properties using reflection:

object request = pireq.GetValue(pendingRequest, null);
object response = piresp.GetValue(pendingRequest, null);

Generic classes and Component services

I recently wrote a lightweight generic data access layer with generic list functionality. Everything worked fine until I had to implement a derived class as a Serviced Component. Turns out classes with generic methods cannot be added to component services, regsvcs.exe gives the following error

An unknown exception occurred during installation:
1: System.Reflection.ReflectionTypeLoadException - Unable to load one or more of the requested types. Retrieve the LoaderExceptions property for more information.

Searched Google, and found 2 hits. If that happens you know trouble is looming on the horizon...

It appears to be a known bug, see the details here.

So for now I had to implement a workaround by not having my class derive from the generic base class but instead to have a private instance of it.

C# generics and testing

The power of C# generics, you just gotta love it.

I'm writing NUnit unit tests for the business objects of the application. All the factory objects happen to have a LoadById method that takes an int as parameter, and return a typed list.

This is beautiful, as I can write a generic test method that for the factory type and list type, and then just write a one-liner test for every factory I want to test.

The generic method:

    public void TestGeneric(int logicalRecord) where L : new()
    {
        L list = new L();
        Type x = typeof(L);
        MethodInfo LoadMethod = x.GetMethod("LoadById");
        List records = (List)LoadMethod.Invoke(list, new object[] { logicalRecord });
        Assert.IsTrue(records.Count > 0);
    }

Invoking the generic method with the Factory type and the List type

            TestGeneric(logicalRecord);

You just gotta love generics. More info here