How would I add a method to all gameobjects?

Questions & Answers
1

I’m sure a lot of this is not the correct way to do things, but I’m just getting started with C# and with Unity, so please bear with me on this one.

I’m trying to implement a simple “use” system so players can press E while looking at a gameobject and have it execute the “use” method stored on that gameobject. I have a very simple version of it working that turns a cube red when a player looks at it and presses E.

The issue I’m running into is that in order to even attempt to call the use() method I have in a script, added as a component to this cube, I have to guarantee to the compiler that the use() method exists, by first searching for the component containing the use() method via

gameObject.GetComponent<ColorChangeBlock>()

This would work fine if I wanted each and every usable item to act identically when used.

So I need to know how I can make this work. I think ideally I’d like to create a “useable” class with an empty default use function and have every gameobject extend that, but I’m not sure how I would go about doing that.

I’m very likely going about this all wrong, and I would love it if someone with more knowledge on the subject could help me out.

2

What you’re looking for is probably Inheritance.

Have something along the lines of:

public abstract class UsableItem : MonoBehaviour {

	// Abstract fields, properties and methods HAVE to be overriden by an inheriting type.
	public abstract void Use() {}
}

public class ColorChangingItem : UsableItem {

	public Renderer Renderer { get; private set; } 

	void Start() {
		Renderer = GetComponent<Renderer>();
	}

	// Override the abstract method
	public override void Use() {
		// Set color to black on player use.
		Renderer.material.SetColor(Color.black);
	}
}

public class MovingItem : UsableItem {

	// Override the abstract method
	public override void Use() {
		// Move this object up .5 units every time the player uses it.
		transform.Translate(new Vector3(0f, 0.5f, 0f));
	}
}

And now you can attach MovingItem and ColorChangingItem to ANY GameObject, just like a normal Component/Script/MonoBehaviour. Then, when your player uses the item do:

UsableItem item = usedItem.GetComponent<UsableItem>();
if (item) item.Use();

And the method call will be dispatched accordingly to the overridden Use function, if any.

…Side Note… Instead, you could use SendMessage:

usedItem.SendMessage("Use", SendMessageOptions.DontRequireReceiver);

However, this uses .NET Reflection, which is significantly slower than simply null-checking the component, like I did above.

3

Hey, @phxvyper thanks for the help.

Edit: Except never mind that’s my bad I wasn’t doing

public class ColorChangeBlock : UsableItem {

Thanks again!

I’m just now back at trying to implement this and I’m getting an error with my color change and moving item code where it’s telling me that

`ColorChangeBlock.Use()' is marked as an override but no suitable method found to override

Any clue what would cause this?

The entire code for the color change block is

public class ColorChangeBlock : MonoBehaviour {
    public override void Use() {
        gameObject.GetComponent<Renderer>().material.color = Color.red;
    }
}

With my UsableItem code being

public abstract class UsableItem : MonoBehaviour {
    public abstract void Use();
}