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Design smell: call overridable methods in constructors

This is another good question I got while teaching the C# Advanced course at SoftUni. Here is a detailed answer.


Why shouldn’t we call virtual methods within the constructor of a base class?


This is actually one of the Code Quality warnings under the Usage section. Please see the link here:

While the article is correct, I’m not sure the explanation is very understandable.

It all comes down to the following execution path:

  • You instantiate the derived class
  • The base class constructor is called
  • It calls virtual methods overridden in the derived class
  • But our derived class’s constructor has not been called yet

Here is my example:

    public abstract class BaseClass
public BaseClass()
Console.WriteLine(“BaseClass constructor called.”);


public virtual void VirtualMethod()
Console.WriteLine(“Base virtual method called”);

public abstract void AbstractMethod();

public class DerivedClass : BaseClass
public DerivedClass()
Console.WriteLine(“Derived class constructor executed VERY late.”);

public override void VirtualMethod()

Console.WriteLine(“Derived Virtual Method”);

public override void AbstractMethod()
Console.WriteLine(“Derived Abstract Method”);

The result:

BaseClass constructor called.

Base virtual method called

Derived Virtual Method

Derived Abstract Method

Derived class constructor executed VERY late.

So we just ran code in a class which might very well be in an invalid state. Objects should go through construction logic first before we execute their methods.