Difference between this and base

this represents the current class instance while base the parent. Example of usage:

public class Parent
{
    public virtual void Foo()
    {
    }
}

public class Child : Parent
{
    // call constructor in the current type
    public Child() : this("abc")
    {
    }

    public Child(string id)
    {
    }

    public override void Foo()
    { 
        // call parent method
        base.Foo();
    }
}

The two keywords are very different.

• this refers to the current instance (not the “current class”). It can only be used in non-static methods (because in a static method there is no current instance). Calling a method on this will call the method in the same way as it would if you called it on a variable containing the same instance.

• base is a keyword that allows inherited method call, i.e. it calls the specified method from the base type. It too can only be used in a non-static method. It is usually used in a virtual method override, but actually can be used to call any method in the base type. It is very different from normal method invocation because it circumvents the normal virtual-method dispatch: it calls the base method directly even if it is virtual.

Darin is right on. An example may also help. (There wasn't an example when I initially posted. Now there is.)

class Base {

    protected virtual void SayHi() {
        Console.WriteLine("Base says hi!");
    }

}

class Derived : Base {

    protected override void SayHi() {
        Console.WriteLine("Derived says hi!");
    }

    public void DoIt() {
        base.SayHi();
        this.SayHi();
    }
}

The above prints "Base says hi!" followed by "Derived says hi!"