How do I generate a random batch of GameObjects associated with some other GameObject?

Questions & Answers
1

In my game, my Player GameObject will hold four cards, which are also GameObjects with a CardObject script attached:

CardObject.cs

using UnityEngine;
using System.Collections;

public class CardObject : MonoBehaviour 
{
	public int value;
	public int color;
}

The Player object accepts a card prefab as a public variable. I then clone four cards and keep reference to them in a List, like so:

PlayerObject.cs

using UnityEngine;
using System.Collections;
using System.Collections.Generic;

public class PlayerObject : MonoBehaviour
{
	public GameObject card;
	private List<CardObject> cards;

	void Start()
	{
		GenerateCards();
	}

	void GenerateCards()
	{
		cards = new List<CardObject>();

		for (int i = 0; i < 4; i++) 
		{
			var c = Instantiate(card, Vector2.zero, Quaternion.identity) as CardObject;
			c.value = Random.Range(1, 9);
			c.color = Random.Range(0, 2);
			cards.Add(c);
		}
	}
}

First of all, I’m getting a non-fatal error:

NullReferenceException: Object reference not set to an instance of an object
PlayerObject.GenerateCards () (at Assets/Scripts/PlayerObject.cs:26)
PlayerObject.Start () (at Assets/Scripts/PlayerObject.cs:16)

But I’m not sure why.

Secondly, if you were implementing similar, would you recommend this method? I am particularly interested in the best way to generate a lot of random content at runtime, and load it into the scene. One of the problems I will face is how to reference each created object? Presumably storing them in a list I can then reference later is the way, but the above error seems to suggest I’m doing it wrong.

2

I have resolved that the main problem here is that I’m passing a GameObject, card, to the PlayerObject script and trying to instantiate it, but my list is expecting the script component CardObject, which is not the same thing.

So the list needs to hold the card GameObject, and then I can get the components via obj.GetComponent.value, etc.

3

Try this:

 void GenerateCards() {
	cards = new List<CardObject>();
	for (int i = 0; i < 4; i++) {
		GameObject newCard = Instantiate(card, Vector2.zero, Quaternion.identity) as GameObject;
		CardObject c = newCard.GetComponent<CardObject>();
		c.value = Random.Range(1, 9);
		c.color = Random.Range(0, 2);
		cards.Add(c);
	}
}