About base in C#

Max Albish

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

6 Replies

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Vulpes12y ago
Accepted 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.
Max Albish12y ago
thank you verymuch +
Max Albish12y ago
Great ! but i ask how to get runtime value like getType even i invok base ?
Vulpes12y ago
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'.
Max Power12y ago
Thanks a lot but how to creat function act like that ?
Vulpes12y ago
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.