Virtual Methods and Overriding

Objective: Override parent Class methods with a child’s method.

In C#, we can inherit from MonoBehaviour Classes. Imagine we’re creating a pet system in our game. Let’s start by creating a Pet Class.

using UnityEngine;

public class Pet : MonoBehaviour {
    
    //the new keyword is used because Unity has an internal variable also
    //called name so we're overriding it to be our own in this instance
    public new string name;

    public void Speak() {
        Debug.Log("Speaking!");
    }
}

To run and test our game, we have a short PetGame script and set up our Scene:

using UnityEngine;

public class PetGame : MonoBehaviour {

    [SerializeField] private Pet pet;

    void Start() {
        pet.Speak();
    }
}

When we press Play, our Duck says “Speaking!” instead of what would make more sense, like “Quack!”. To solve this, we can create a Duck class that inherits Pet. In Pet, we will need to allow children Classes to be able to override the Speak method by declaring Speak as a virtual method. virtual allows us to override from any Class that inherits Pet.

using UnityEngine;

public class Pet : MonoBehaviour {
    
    public new string name;

    public virtual void Speak() {
        Debug.Log("Speaking!");
    }
}

Then in Duck, we can override the Speak method like so using override:

using UnityEngine;

public class Duck : Pet {
    
    public override void Speak() {
        Debug.Log("Quack!");
    }
}

Keep in mind, the children and parent’s variables/methods both have to be stated as the same access modifier. So the Speak method in both Classes need to be public in our case.