如何使用滑块创建和销毁对象？

Question

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

[ExecuteInEditMode]
public class GameManager : MonoBehaviour
{
    public GameObject prefabToDraw;
    [Range(0, 100)]
    public int amountOfObjects;

    private int amountCopy;

    // Use this for initialization
    void Start()
    {
        amountCopy = amountOfObjects;
        prefabToDraw.tag = "DrawPrefab";
    }

    // Update is called once per frame
    void Update()
    {
        if (amountOfObjects > amountCopy && amountCopy != amountOfObjects)
        {
            for (int i = 0; i < amountOfObjects; i++)
            {
                Instantiate(prefabToDraw);
            }

            amountCopy = amountOfObjects;
        }

        if (amountOfObjects == 0)
        {
            var gos = GameObject.FindGameObjectsWithTag("DrawPrefab");

            for (int i = 0; i < gos.Length; i++)
            {
                DestroyImmediate(gos[i]);
            }
        }
    }
}

Without this part it will work fine only for creating objects:

if (amountOfObjects == 0)
            {
                var gos = GameObject.FindGameObjectsWithTag("DrawPrefab");

                for (int i = 0; i < gos.Length; i++)
                {
                    DestroyImmediate(gos[i]);
                }
            }

But I want to do that when the slider is moving to the right more amount of objects create more new and this is working.

When moving the slider to the left less amount of objects then destroy objects for example if there are 90 objects and the slider is on value 90 and now I'm moving the slider to the left start destroy objects if I moved it from 90 to 70 it should destroy 20 objects if moved to the right again create new again.

I'm not sure how to do the destroy part.

I tried:

if (amountOfObjects == 0)
        {
            var gos = GameObject.FindGameObjectsWithTag("DrawPrefab");

            for (int i = 0; i < gos.Length; i++)
            {
                DestroyImmediate(gos[i]);
            }
        }

But once there is even one object with tag "DrawPrefab" the object will be destroy even if it's not 0. I messed it up.

UPDATE

This is what I tried:

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

[ExecuteInEditMode]
public class GameManager : MonoBehaviour
{
    public GameObject prefabToDraw;
    [Range(0, 100)]
    public int amountOfObjects;

    private int amountCopy;
    private List<GameObject> gos = new List<GameObject>();

    // Use this for initialization
    void Start()
    {
        amountCopy = amountOfObjects;
    }

    // Update is called once per frame
    void Update()
    {
        CreateObjects();
        DestroySomeObjects(amountOfObjects);
    }

    private void CreateObjects()
    {
        if (amountOfObjects > amountCopy && amountCopy != amountOfObjects)
        {
            for (int i = 0; i < amountOfObjects; i++)
            {
                GameObject go = Instantiate(prefabToDraw);
                gos.Add(go);
            }

            amountCopy = amountOfObjects;
        }
    }

    private void DestroySomeObjects(int amountFromRightSide)
    {
        if (gos.Count != 0)
        {
            for (int i = gos.Count - 1; i <= gos.Count - amountFromRightSide; i--)
            {
                DestroyImmediate(gos[i]);
            }
        }
    }

    private void DestroyAllObjects()
    {
        if (gos.Count != 0)
        {
            foreach (GameObject go in gos)
            {
                DestroyImmediate(go);
            }
        }
    }
}

When moving the slider to the right it's creating and adding new objects but when moving to the left it's giving exception: ArgumentOutOfRangeException: Argument is out of range. parameter name index.

On the lines:

DestroySomeObjects(amountOfObjects);

And

DestroyImmediate(gos[i]);

Answer 1

If you always have the same amount of objects, I suggest that you enable/disable them instead of destroying them, as this is more performance friendly.

I would also store the created objects in a list to have a reference to them, instead of finding them afterwards with another method.

List<GameObject> gos = new List<GameObject>();
void CreateObjects()
{
    if (amountOfObjects > amountCopy && amountCopy != amountOfObjects)
    {
        for (int i = 0; i < amountOfObjects; i++)
        {
            GameObject go = Instantiate(prefabToDraw);
            gos.Add(go);
        }

        amountCopy = amountOfObjects;
    }
}

That way you can use the list when destroying or doing other things.

void DestroySomeObjects(int amountFromRightSide)
{
    if (gos.Count != 0)
        {
            for (int i = gos.Count-1; i <= gos.Count-amountFromRightSide; i--)
            {
                DestroyImmediate(gos[i]);
            }
        } 
}

void DestroyAllObjects()
{
    if (gos.Count != 0)
        {
            foreach (GameObject go in gos)
            {
                DestroyImmediate(go);
            }
        } 
}