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Question by BDR530 · May 29, 2020 at 01:41 PM · 2dlistinstancedontdestroyonloadsingleton

DontDestroyOnLoad & Singleton

Hi, in my 2D game i'm trying to use the same list of gameobjects for every scene with this code:

 public class GameManager : MonoBehaviour
 {
     public static GameManager instance;
     public static GameObject cities;
     public static List<GameObject> citiesList = new List<GameObject>();
 
     void Awake()
     {
         cities = GameObject.Find("Cities");
 
         if (instance != null)
             Destroy(cities);
         else
         {
             instance = this;
             citiesList.AddRange(GameObject.FindGameObjectsWithTag("City")); //Children of Cities
             DontDestroyOnLoad(cities);
         }
     }
 }

With this method the game object "Cities" is duplicated in each scene. How can i avoid this?

Thanks!

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Answer by Mateo03 · May 29, 2020 at 03:04 PM

  public class GameManager : MonoBehaviour
  {
      public static GameManager instance;
      public static GameObject cities;
      public static List<GameObject> citiesList = new List<GameObject>();
  
      void Awake()
      {
          cities = GameObject.Find("Cities");
  
          if (instance != null && instance != this)
              Destroy(this.gameObject);
          else
          {
              instance = this;
              citiesList.AddRange(GameObject.FindGameObjectsWithTag("City")); //Children of Cities
              DontDestroyOnLoad(cities);
          }
      }
  }
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avatar image Mateo03 · May 29, 2020 at 03:05 PM 0
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Try with this code. You should destroy the gameObject that isn't the instance (the duplicated one) in Awake.

avatar image BDR530 · May 29, 2020 at 04:38 PM 0
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Thanks, i tried this but i still have the same problem, the game object "Cities" is still duplicated.

avatar image BDR530 · May 29, 2020 at 10:25 PM 0
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I used a separate class for that specific object and now it works:

 public class Cities$$anonymous$$anager : $$anonymous$$onoBehaviour
 {
     public static Cities$$anonymous$$anager instance;
     void Awake()
     {
         if (instance != null && instance != this)
             Destroy(this.gameObject);
         else
         {
             instance = this;
             DontDestroyOnLoad(this.gameObject);
         }
     }
 }
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1

Answer by viesc123 · May 29, 2020 at 05:08 PM

Every time you load a new scene, your GameManager will be destroyed, because you only set "cities" to be permanent. Therefore, instance will always be null in Awake. The condition should be

 if (citiesList.Count > 0)
     Destroy(cities);

to check if you already have objects stored. Or you could add a line, making the GameManager permanent too. Then you'd have to delete the new instance like Mateo showed.

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