How does DontDestroyOnLoad working?

Question

Every time when the scene has been load(in the same scene), some code in awake is running and something is not.

 public class ScenesManager : MonoBehaviour
 {
     public List<int> test;
 
     private void Awake()
     {
         DontDestroyOnLoad(gameObject);
         test = new List<int>();//this code have not run
         Debug.Log("test is the new List now");//this code is running
     }
 
 }

Answer 1

So do you have this SceneManager class setup as a singleton?? Because if it is not a singleton, you are creating a new instance of this class every time you reload the scene. If this is the case, you will have to rethink what you are doing. Consider the following: (a very simple singleton implementation)

 public class ScenesManager : MonoBehaviour
  {
      public List<int> test;
  
      private void Awake()
      {
          ScenesManager _instances = FindObejctsOfType<ScenesManager>();
          
          if( _instances.Length > 1 )
          {
               for( int i = 0; i < _instances.Length; i++)
               {
                    if( _instances[i] != null && _instances[i] != this )
                    {
                        Destroy( this.gameObject );
                        return;
                    }
               }
          }
          DontDestroyOnLoad(gameObject);
          test = new List<int>();//this code have not run
          Debug.Log("test is the new List now");//this code is running
      }
  
  }

Answer 2

Answer by CmdrZin · Dec 23, 2020 at 08:03 AM

What ever GameObject that this script is attached to does not go away when the scene it is in is replaced by another scene. The GameObject is persistent form scene to scene. See also https://docs.unity3d.com/ScriptReference/Object.DontDestroyOnLoad.html

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How does DontDestroyOnLoad working?

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