How do I check if a type is a subtype OR the type of an object

Question

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

User · Answer

I m posting this answer with the hope of someone sharing with me if and why it would be a bad idea   In my application  I have a property of Type that I want to check to be sure it is typeof A  or typeof B   where B is any class derived from A   So my code   public class A      public class B   A      public class MyClass       private Type  helperType      public Type HelperType               get   return  helperType            set                        var testInstance    A Activator CreateInstance value               if  testInstance  null                  throw new InvalidCastException  HelperType must be derived from A                 helperType   value                      I feel like I might be a bit naive here so any feedback would be welcome

User · Answer

If you re trying to do it in a Xamarin Forms PCL project  the above solutions using IsAssignableFrom gives an error      Error   Type  does not contain a definition for  IsAssignableFrom  and   no extension method  IsAssignableFrom  accepting a first argument of   type  Type  could be found  are you missing a using directive or an   assembly reference     because IsAssignableFrom asks for a TypeInfo object  You can use the GetTypeInfo   method from System Reflection   typeof BaseClass  GetTypeInfo   IsAssignableFrom typeof unknownType  GetTypeInfo

User · Answer

You should try using Type IsAssignableFrom instead

User · Answer

typeof BaseClass  IsAssignableFrom unknownType

User · Answer

Apparently  no   Here s the options    Use Type IsSubclassOf Use Type IsAssignableFrom is and as   Type IsSubclassOf  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 Baseis  obviously  not a subclass of itself   Type IsAssignableFrom  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   Conclusion  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

[c#] How do I check if a type is a subtype OR the type of an object?

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