Object Pooling

I am trying to make this code works, I have 6 prefab scenarios that I want to use in my game. in the start function I made 3 copies of each prefab, making a total of 18 pooled objects in the game.

when the function spawntile() is called I want that one of this 18 pooled objects that is inactive, turns active and show in the gameview. all other parts is working. just the part:

go = ActiveTiles [RandomPrefabIndex].SetActive (true);

go = ActiveTiles [PrefabIndex].SetActive (true);

dont work, I was using:

go = Instantiate (ActiveTiles[RandomPrefabIndex]) as GameObject;

go = Instantiate (ActiveTiles[PrefabIndex]) as GameObject;

and this works but create a new object, and I need the code active one of 18 inactive objects.

I am receiving this erros

error CS1502: The best overloaded method match for System.Collections.Generic.List<UnityEngine.GameObject>.this[int]' has some invalid arguments error CS1503: Argument #1' cannot convert method group' expression to type int' error CS0029: Cannot implicitly convert type void' to UnityEngine.GameObject'

thanks for the help!

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

public class TILEMANAGER : MonoBehaviour {

 public GameObject[] TileSPrefabs;

 private Transform PlayerTransform;
 private float SpawnZ = -10.0f;
 private float TileLenght = 10.0f;
 private float SafeZone = 15.0f;
 private int AmountTilesOnScreen = 8;
 private int LastPrefabIndex = 0;
 private int PooledTiles = 3;

 private List<GameObject> ActiveTiles;

 // Use this for initialization
 void Start () {
     ActiveTiles = new List<GameObject> ();
     PlayerTransform = GameObject.FindGameObjectWithTag ("Jogador").transform;

     foreach (GameObject objectprefab in TileSPrefabs){            
         for (int i = 0; i < PooledTiles; i++) {
             GameObject obj = Instantiate (objectprefab) as GameObject;
             obj.SetActive (false);
             ActiveTiles.Add (obj);            
         }
     }

     for (int i = 0; i < AmountTilesOnScreen; i++) {
         if (i < 3)
             SpawnTile (0);
         else
             SpawnTile ();
     }
 }

 // Update is called once per frame
 void Update () {
     if (PlayerTransform.position.z - SafeZone > (SpawnZ - AmountTilesOnScreen * TileLenght)) {
         SpawnTile ();
         DeleteTile ();
     }

 }

 void SpawnTile(int PrefabIndex = -1){
     GameObject go;
     if (PrefabIndex == -1)
         // the error is here//
         go = ActiveTiles [RandomPrefabIndex].SetActive (true);
     else
         // and here//
         go = ActiveTiles [PrefabIndex].SetActive (true);
     go.transform.SetParent (transform);
     go.transform.position = Vector3.forward * SpawnZ;
     SpawnZ += TileLenght;
     ActiveTiles.Add (go);
 }

 void DeleteTile(){
     ActiveTiles [0].SetActive (false);
 }

 private int RandomPrefabIndex(){
     if (ActiveTiles.Count <= 1)
         return 0;

     int RandomIndex = LastPrefabIndex;
     while (RandomIndex == LastPrefabIndex) {
         RandomIndex = Random.Range (0, ActiveTiles.Count);
     }

     LastPrefabIndex = RandomIndex;
     return RandomIndex;
 }

}