To check if a type is a subclass of another type in C#, it's easy:
typeof (SubClass).IsSubclassOf(typeof (BaseClass)); // returns true
However, this will fail:
typeof (BaseClass).IsSubclassOf(typeof (BaseClass)); // returns false
Is there any way to check whether a type is either a subclass OR of the base class itself, without using an OR
operator or using an extension method?
Apparently, no.
Here's the options:
is
and as
As you've already found out, this will not work if the two types are the same, here's a sample LINQPad program that demonstrates:
void Main()
{
typeof(Derived).IsSubclassOf(typeof(Base)).Dump();
typeof(Base).IsSubclassOf(typeof(Base)).Dump();
}
public class Base { }
public class Derived : Base { }
Output:
True
False
Which indicates that Derived
is a subclass of Base
, but that Base
is (obviously) not a subclass of itself.
Now, this will answer your particular question, but it will also give you false positives. As Eric Lippert has pointed out in the comments, while the method will indeed return True
for the two above questions, it will also return True
for these, which you probably don't want:
void Main()
{
typeof(Base).IsAssignableFrom(typeof(Derived)).Dump();
typeof(Base).IsAssignableFrom(typeof(Base)).Dump();
typeof(int[]).IsAssignableFrom(typeof(uint[])).Dump();
}
public class Base { }
public class Derived : Base { }
Here you get the following output:
True
True
True
The last True
there would indicate, if the method only answered the question asked, that uint[]
inherits from int[]
or that they're the same type, which clearly is not the case.
So IsAssignableFrom
is not entirely correct either.
is
and as
The "problem" with is
and as
in the context of your question is that they will require you to operate on the objects and write one of the types directly in code, and not work with Type
objects.
In other words, this won't compile:
SubClass is BaseClass
^--+---^
|
+-- need object reference here
nor will this:
typeof(SubClass) is typeof(BaseClass)
^-------+-------^
|
+-- need type name here, not Type object
nor will this:
typeof(SubClass) is BaseClass
^------+-------^
|
+-- this returns a Type object, And "System.Type" does not
inherit from BaseClass
While the above methods might fit your needs, the only correct answer to your question (as I see it) is that you will need an extra check:
typeof(Derived).IsSubclassOf(typeof(Base)) || typeof(Derived) == typeof(Base);
which of course makes more sense in a method:
public bool IsSameOrSubclass(Type potentialBase, Type potentialDescendant)
{
return potentialDescendant.IsSubclassOf(potentialBase)
|| potentialDescendant == potentialBase;
}