How to get base class's generic type parameter?

Question

I have three class as following:

public class TestEntity { }  public class BaseClass<TEntity> { }  public class DerivedClass : BaseClass<TestEntity> { } 

I already get the System.Type object of DerivedClass using reflection in runtime. How can I get the System.Type object of TestEntity using reflection?

Thanks.

Answer 1

I assume that your code is just a sample and you don't explicitly know DerivedClass.

var type = GetSomeType(); var innerType = type.BaseType.GetGenericArguments()[0]; 

Note that this code can fail very easily at run time you should verify if type you handle is what you expect it to be:

if(type.BaseType.IsGenericType       && type.BaseType.GetGenericTypeDefinition() == typeof(BaseClass<>)) 

Also there can be deeper inheritance tree so some loop with above condition would be required.

Answer 2

You can use the BaseType property. The following code would be resilient for changes in the inheritance (e.g. if you add another class in the middle):

Type GetBaseType(Type type) {    while (type.BaseType != null)    {       type = type.BaseType;       if (type.IsGenericType && type.GetGenericTypeDefinition() == typeof(BaseClass<>))       {           return type.GetGenericArguments()[0];       }    }    throw new InvalidOperationException("Base type was not found"); }  // to use: GetBaseType(typeof(DerivedClass))