Question

I’m trying to call a generic method I’ve created called LoadItems<T>(). This method does a bunch of operations on a List<T> of items it returns from the database.

The problem I have is in calling the LoadItems<T>() method. All I have to work with is an object. I want to resolve this object into a T so that I can call my method.

In a pseudo way of explaining:

object theObject = GetTheObject();
LoadItems<GetGenericType(theObject)>();

Is there any way to do this?

Thanks a ton

Answer 1

You’ll have to use reflection or change your design.

If you want to use reflection, the process is complicated:

// get the type of the object variable
var objType = theObject.GetType();

// I'm assuming that LoadItems() is a method in the current class
var selfType = GetType();

// you might need to use an overload of GetMethod() -- please read the documentation!
var methodInfo = selfType.GetMethod("LoadItems");

// this fills in the generic arguments
var genericMethodInfo = methodInfo.MakeGenericMethod(new[] { objType });

// this calls LoadItems<T>() with T filled in; I'm assuming it's a method on this class
var results = genericMethodInfo.Invoke(this, null);

Note that results will be an object. If you want it to be a specific List<> type, you’re out of luck. You don’t know what the type is at compile time. You can cast it to the non-generic IList, or use some LINQ expression to convert it to something more useful, like this:

var niceResults = results.Cast<SomeBaseType>().ToList();

As always, read the documentation on the functions I listed above if you aren’t sure what’s going on.