About base in C#

Question

namespace contest { class Program { static void Main ( string [] args ) { B b = new B (); } } class A { public A () { k (); } private void k () { Console . WriteLine ( base . GetType (). Name ); } } class B : A { } } Can someone tell me why it outputs B instead of Object doesn't base.GetType() get A's parent object therefore the root Object? Thanks a lot

Vulpes · Answer

Well as the program stands if you change the method to this it would print 'Object': private void k() { Console.WriteLine(base.GetType() .BaseType.BaseType .Name); } However this only works because 'base' here - as previously discussed - is really an instance of B. If it were an instance of A you'd get a NullReferenceException because System.Object doesn't have a base class. There is a way to always get 'Object' without using typeof(A): using System; using System.Reflection; namespace contest { class Program { static void Main(string[] args) { B b = new B(); A a = new A(); } } class A { public A() { k(); } private void k() { Console.WriteLine(MethodBase.GetCurrentMethod().DeclaringType.BaseType.Name); } } class B : A { } } The output is: Object Object However we're having to use reflection to do this and so the code is relatively slow to execute.

Vulpes · Answer

You could do this: using System; namespace contest { class Program { static void Main(string[] args) { B b = new B(); } } class A { public A() { k(); } private void k() { Console.WriteLine( typeof(A).BaseType.Name ); } } class B : A { } } The output is now 'Object'.

Vulpes · Answer

The GetType() method always returns the 'runtime' type of the current instance. The 'base' keyword doesn't alter the type of the current instance - it merely enables you to access base class members through that instance which might otherwise be hidden. So in this case the current instance is of type B (even though its accessing code in its base class A) and so that's what base.GetType().Name returns. If you changed your Main method to this: static void Main(string[] args) { B b = new B(); A a = new A(); } you'd find that the second line printed out A because that's now the runtime type of the current instance.

Max Albish · Answer

thank you verymuch +

Max Albish · Answer

Great ! but i ask how to get runtime value like getType even i invok base ?

Max Power · Answer

Thanks a lot but how to creat function act like that ?