如何使克隆的游戏对象成为全局对象，以便可以在Unity功能之外使用它们？

Question

I just recently got into Unity 3D and currently working on one of my first own projects. For the game im making, I need a spawner function, that respawns a clone of the enemy as soon as the enemy falls off the platform. This is the code I have right now:

using UnityEngine;

public class spawner : MonoBehaviour
{
    public GameObject enemyPrefab;
    public float spawnHeight = 0.75f;

    // Start is called before the first frame update
    void Start()
    {
        spawnEnemy();
    }

    // Update is called once per frame
    void Update()
    {
        if (enemyClone.transform.position.y < -10)
        {
            Destroy(enemyClone);
            spawnEnemy();
        }
    }

    public void spawnEnemy()
    {
        var enemyPosition = new Vector3(Random.Range(-5, 5), spawnHeight, Random.Range(-5, 5));
        var enemyClone = Instantiate(enemyPrefab, enemyPosition, Quaternion.identity);
    }
}

The function spawnEnemy itself works fine, since it creates an enemy on game start, tho further enemies aren't spawned. I get the message: "Assets\\spawner.cs(21,21): error CS0103: The name 'enemyClone' does not exist in the current context".

I do see why I get the message, don't know how to make enemyClone globally available however.

Thanks to everybody in advance,

bezunyl

Answer 1

In the spawnEnemy() function, you say var enemyClone = Instantiate(...); . enemyClone is a local variable that can only be used within the spawnEnemy function, or at least that's how you've written it.

If you want to use the enemyClone outside of the spawnEnemy function, you need to declare the enemyClone variable outside of the function. (The example below will work if you DON'T want enemyClone to be accessible to other GameObjects)

using UnityEngine;

public class spawner : MonoBehaviour
{
    public GameObject enemyPrefab;
    public float spawnHeight = 0.75f;

    private GameObject enemyClone //Added to allow enemyClone to be used anywhere in the class

    // Start is called before the first frame update
    void Start()
    {
        spawnEnemy();
    }

    // Update is called once per frame
    void Update()
    {
        if (enemyClone.transform.position.y < -10)
        {
            Destroy(enemyClone);
            spawnEnemy();
        }
    }

    public void spawnEnemy()
    {
        var enemyPosition = new Vector3(Random.Range(-5, 5), spawnHeight, Random.Range(-5, 5));
        enemyClone = Instantiate(enemyPrefab, enemyPosition, Quaternion.identity);
    }
}

Now if you want enemyClone to be accessible by other GameObjects, then you'll want to make the enemyClone variable public instead of private . If you don't want it to show up in the inspector, add [HideInInspector] above the declaration of enemyClone, as shown below:

[HideInInspector]
public GameObject enemyClone;

Your issue is based on scope . You might want to research it, it's important to know.

The scope of a variable determines its visibility to the rest of a program.

http://www.blackwasp.co.uk/CSharpVariableScopes.aspx http://www.informit.com/articles/article.aspx?p=1609145&seqNum=4

Answer 2

Spawning GameObject on demand is expensive. Instead of spawning it everytime, you should pool the GameObject.

public class Spawner : MonoBehaviour {
    public Enemy enemyPrefab;
    public List<Enemy> enemyPool;
    public const SPAWN_HEIGHT = 0.75f;

    // Start is called before the first frame update
    void Start()
    {
        enemyPool = new List<Enemy>();
        spawnEnemy();
    }

    // Update is called once per frame
    public void Despawn(Enemy deadEnemy)
    {
        deadEnemy.gameObject.SetActive(false);
        enemyPool.Add(deadEnemy);
    }

    public void spawnEnemy() {
        Enemy newEnemy;
        if (enemyPool.Count > 0) {
            newEnemy = enemyPool[0];
            enemyPool.Remove(0);
        } else {
            newEnemy = Instantiate(enemyPrefab);
        }
        newEnemy.Init(this);

        newEnemy.position =  new Vector3(Random.Range(-5, 5), SPAWN_HEIGHT, Random.Range(-5, 5));
        newEnemy.gameObject.SetActive(true);
    }
}

public class Enemy : MonoBehaviour {
    private Spawner spawner;
    private const float DEATH_POSITION_Y = -10;

    public void Init(Spawner spawner) {
        this.spawner = spawner;
    }

    void Update() {
        if (transform.position.y < DEATH_POSITION_Y) {
            spawner.Despawn(this);
        }
    }
}