将：base放在功能后面？

Question

 public LocalizedDisplayNameAttribute(string displayNameKey)
            : base(displayNameKey)
        {

        }

if i put :base after the function in the class what does that mean?

Answer 1

base indicates that you're calling the base class' constructor from this class' constructor.

It is only valid for constructors, not regular methods. In your case, when a LocalizedDisplayNameAttribute is created, it passes the displayNameKey parameter to its base class' constructor.

Answer 2

It means that you will invoke the according constructor of the base class of your class.

Consider this:

public class A {
  public A() {
    Console.WriteLine("You called the first constructor");
  }
  public A(int x) {
    Console.WriteLine("You called the second constructor with " + x);
  }
}

public class B : A {
  public B() : base() { } // Calls the A() constructor
}

public class C : A {
  public C() : base(10) { } // Calls the A(int x) constructor
}

public class D : A {
  public D() { } // No explicit base call; Will call the A() constructor
}


...
new B(); // Will print "You called the first constructor"
new C(); // Will print "You called the second constructor with 10"
new D(); // Will print "You called the first constructor"

If this still doesn't make any sense, you should probably read a bit more about constructors in object oriented languages, for example here .

Answer 3

What you have there is a Constructor and not a function or method (a constructor is a special method that is called automatically when your class is instantiated). Adding :base (parameter) after the constructor allows you to call the constructor of the base class (the class your class inherited from) with the parameter passed into your class constructor.

A good tutorial on constructors can be found at http://www.yoda.arachsys.com/csharp/constructors.html which should help clear this up.