Classes and Inheritance - Illustrated C# 2005 - page 154

For example, in the following code, the values of MyField1 and MyField2 would be set to 5
and 0 respectively, before the base class constructor was called.

class MyDerivedClass : MyBaseClass
{
int MyField1 = 5; // 1. Member initialized.
int MyField2; // Member initialized.

public MyDerivedClass() // 3. Body of constructor executed.
{
...
}
}

class MyBaseClass
{
public MyBaseClass() // 2. Base class constructor called.
{
...
}
}

■ Caution Calling a virtual method in a constructor is strongly discouraged . The virtual method in the base
class would call the override method in the derived class while the base class constructor was being exe-
cuted. But that would be before the derived constructor's body was executed. It would, therefore, be calling
up into the derived class before the class was completely initialized.

Constructor Initializers
By default, the parameterless constructor of the base class is called when an object is being
constructed. But constructors can be overloaded, so a base class might have more than one. If
you want your derived class to use a specific base class constructor other than the parameter-
less constructor, you must specify it in a constructor initializer .
There are two forms of constructor initializer:

The first form uses the keyword base and specifies which base class constructor to use.

￿

￿ The second form uses the keyword this and specifies which other constructor from this

class should be used.

A base class constructor initializer is placed after a colon following the parameter list in a
class's constructor declaration. The constructor initializer consists of the keyword base , and
the parameter list of the base constructor to call.