Unity 3D - 如何在僵尸全部死后重生？

Question

I'm trying to make a simple 3D fps. right now, I'm working on randomly spawning zombies. The only problem is that after the zombies spawn and I shoot them, they don't respawn. How can I make it so that after 10 seconds for example, another set of zombies appear?

Here is my zombie spawner script:

using System.Collections;
using UnityEngine;

public class GenerateEnemies : MonoBehaviour
{
public GameObject theEnemy;
public float xPos;
public float zPos;
public int enemyCount;

// Start is called before the first frame update
void Start()
{
    StartCoroutine(EnemyDrop1());
    StartCoroutine(EnemyDrop2());
    StartCoroutine(EnemyDrop3());
    StartCoroutine(EnemyDrop4());
}

IEnumerator EnemyDrop1()
{
    while(enemyCount < 5)
    {
        xPos = Random.Range(-22, -130);
        zPos = Random.Range(135, -135);
        Instantiate(theEnemy, new Vector3(xPos, 1, zPos), Quaternion.identity);
        yield return new WaitForSeconds(0.1f);
        enemyCount += 1;
    }
}

IEnumerator EnemyDrop2()
{
    while (enemyCount < 10)
    {
        xPos = Random.Range(-23, 134);
        zPos = Random.Range(-75, -135);
        Instantiate(theEnemy, new Vector3(xPos, 1, zPos), Quaternion.identity);
        yield return new WaitForSeconds(0.1f);
        enemyCount += 1;
    }
}

IEnumerator EnemyDrop3()
{
    while (enemyCount < 15)
    {
        xPos = Random.Range(30, 130);
        zPos = Random.Range(-75, 135);
        Instantiate(theEnemy, new Vector3(xPos, 1, zPos), Quaternion.identity);
        yield return new WaitForSeconds(0.1f);
        enemyCount += 1;
    }
}

IEnumerator EnemyDrop4()
{
    while (enemyCount < 20)
    {
        xPos = Random.Range(-22, -130);
        zPos = Random.Range(135, -135);
        Instantiate(theEnemy, new Vector3(xPos, 1, zPos), Quaternion.identity);
        yield return new WaitForSeconds(0.1f);
        enemyCount += 1;
    }
}
}

by the way, I did the script this way so that the zombies don't spawn too close to the player.

I'm new at unity, so if you do have an answer, please explain it. Thanks:)

Answer 1

Why zombies won't re-spawn

There are a couple of potential reasons on why your zombies stop respawning:

1. The code sample you provided doesn't subtract anything from enemyCount . Assuming that is also the case everywhere else, it could be the culprit in the issue.
2. The Coroutine methods that contain the while loops, run while a set condition is true. That means that your script will stop spawning enemies altogether as soon as a certain number is reached.
   

I'm gonna assume the 2. point is true in this case.

Solution

A potential solution I would offer is to make the while loops last either forever or using a different condition and put the previously used condition into an if statement. That will make the loops remain functional but skip over the step where a zombie is spawned when there are too many of them.

Here's a modified version of your code:

using System.Collections;
using UnityEngine;

public class GenerateEnemies : MonoBehaviour
{
    public GameObject theEnemy;
    public float xPos;
    public float zPos;
    public int enemyCount;

    private void Start()
    {
        StartCoroutine(EnemyDrop1());
        StartCoroutine(EnemyDrop2());
        StartCoroutine(EnemyDrop3());
        StartCoroutine(EnemyDrop4());
    }

    private IEnumerator EnemyDrop1()
    {
        while (true)
        {
            if (enemyCount >= 5)
            {
                yield return new WaitForSeconds(0.1f);
                continue;
            }

            xPos = Random.Range(-22, -130);
            zPos = Random.Range(135, -135);
            Instantiate(theEnemy, new Vector3(xPos, 1, zPos), Quaternion.identity);
            yield return new WaitForSeconds(0.1f);
            enemyCount += 1;
        }
    }

    private IEnumerator EnemyDrop2()
    {
        while (true)
        {
            if (enemyCount >= 10)
            {
                yield return new WaitForSeconds(0.1f);
                continue;
            }

            xPos = Random.Range(-23, 134);
            zPos = Random.Range(-75, -135);
            Instantiate(theEnemy, new Vector3(xPos, 1, zPos), Quaternion.identity);
            yield return new WaitForSeconds(0.1f);
            enemyCount += 1;
        }
    }

    private IEnumerator EnemyDrop3()
    {
        while (true)
        {
            if (enemyCount >= 15)
            {
                yield return new WaitForSeconds(0.1f);
                continue;
            }

            xPos = Random.Range(30, 130);
            zPos = Random.Range(-75, 135);
            Instantiate(theEnemy, new Vector3(xPos, 1, zPos), Quaternion.identity);
            yield return new WaitForSeconds(0.1f);
            enemyCount += 1;
        }
    }

    private IEnumerator EnemyDrop4()
    {
        while (true)
        {
            if (enemyCount >= 20)
            {
                yield return new WaitForSeconds(0.1f);
                continue;
            }

            xPos = Random.Range(-22, -130);
            zPos = Random.Range(135, -135);
            Instantiate(theEnemy, new Vector3(xPos, 1, zPos), Quaternion.identity);
            yield return new WaitForSeconds(0.1f);
            enemyCount += 1;
        }
    }
}

Here's a slightly refactored version of the same code:

using System.Collections;
using UnityEngine;

public class GenerateEnemies : MonoBehaviour
{
    public GameObject theEnemy;
    public float xPos;
    public float zPos;
    public int enemyCount;

    private void Start()
    {
        StartCoroutine(EnemyDrop(5, -130f, -22f, -135f, 135f));
        StartCoroutine(EnemyDrop(10, -23f, 134f, -135f, -75f));
        StartCoroutine(EnemyDrop(15, 30f, 130f, -75f, 135f));
        StartCoroutine(EnemyDrop(20, -130f, -22f, -135f, 135f));
    }

    private IEnumerator EnemyDrop(
        int maxEnemyCount,
        float minPositionX,
        float maxPositionX,
        float minPositionZ,
        float maxPositionZ)
    {
        while (true)
        {
            if (enemyCount >= maxEnemyCount)
            {
                yield return new WaitForSeconds(0.1f);
                continue;
            }

            xPos = Random.Range(minPositionX, maxPositionX);
            zPos = Random.Range(minPositionZ, maxPositionZ);
            Instantiate(theEnemy, new Vector3(xPos, 1, zPos), Quaternion.identity);
            enemyCount += 1;

            yield return new WaitForSeconds(0.1f);
        }
    }
}

Extra note

If you intend to write a solution where you want to gradually spawn let's say exactly 10 zombies and then stop until there are no zombies again, I'll leave you with the following code sample as a hint (I'll leave the full solution up to you):

private IEnumerator KeepDroppingEnemies()
{
    while (true)
    {
        yield return new WaitUntil(() => enemyCount == 0);
        yield return DropEnemies(10);
    }
}

private IEnumerator DropEnemies(int numberOfEnemies)
{
    for (int i = 0; i < numberOfEnemies; i++)
    {
        // Spawn an enemy

        yield return new WaitForSeconds(0.1f);
    }
}