Call base function then inherited function

Question

I have a base class and a class inheriting base. The base class has several virtual functions that the inherited class may override. However, the virtual functions in the base class has code that MUST to run before the inherited class overrides get called. Is there some way that I can call the base classes virtual functions first then the inherited class overrides. Without making a call to base.function().

I know I can simply make two functions, one that gets called, the other virtual. But is there a way I can keep the same names as well? I know I may need to change some things around.

class myBase {     public virtual myFunction()         { /* must-run code, Called first */ } }  class myInherited : myBase {     public override myFunction()         { /* don't use base.myFunction();,         called from base.myFunction(); */ } } 

Similar question here.

Answer 1

A common solution that can be found in the .NET Framework is to split a method in a public method XXX and a protected, virtual method OnXXX that is called by the public method. For your example, it would look like this:

class MyBase {     public void MyMethod()     {         // do something         OnMyMethod();         // do something     }      protected virtual void OnMyMethod()     {     } } 

and

class MyInherited : MyBase {     protected override void OnMyMethod()     {         // do something     } } 

Answer 2

C# doesn't have support for automatically enforcing this, but you can enforce it by using the template method pattern. For example, imagine you had this code:

abstract class Animal {     public virtual void Speak()     {         Console.WriteLine("I'm an animal.");     } }  class Dog : Animal {     public override void Speak()     {         base.Speak();         Console.WriteLine("I'm a dog.");     } } 

The trouble here is that any class inheriting from Animal needs to call base.Speak(); to ensure the base behavior is executed. You can automatically enforce this by taking the following (slightly different) approach:

abstract class Animal {     public void Speak()     {         Console.WriteLine("I'm an animal.");         DoSpeak();     }      protected abstract void DoSpeak(); }  class Dog : Animal {     protected override void DoSpeak()     {         Console.WriteLine("I'm a dog.");     } } 

In this case, clients still only see the polymorphic Speak method, but the Animal.Speak behavior is guaranteed to execute. The problem is that if you have further inheritance (e.g. class Dachshund : Dog), you have to create yet another abstract method if you want Dog.Speak to be guaranteed to execute.