从Firebase获取数据后尝试更改场景时Unity脚本停止工作

Question

So when I tried to get data from Firebase RealTime Database, the data was received succefuly. But when I tried to change the scene, the script is just stop working. Here is my full script :

using Firebase;
using Firebase.Database;
using Firebase.Extensions;
using Firebase.Unity.Editor;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.SceneManagement;

public class NewBehaviourScript : MonoBehaviour
{
    DependencyStatus dependencyStatus = DependencyStatus.UnavailableOther;
    protected bool isFirebaseInitialized = false;
    // Start is called before the first frame update
    private void Start()
    {

        FirebaseApp.CheckAndFixDependenciesAsync().ContinueWithOnMainThread(task => {
            dependencyStatus = task.Result;
            if (dependencyStatus == DependencyStatus.Available)
            {
                InitializeFirebase();
            }
            else
            {
                Debug.LogError(
                  "Could not resolve all Firebase dependencies: " + dependencyStatus);
            }
        });
    }
    protected virtual void InitializeFirebase()
    {
        FirebaseApp app = FirebaseApp.DefaultInstance;
        // NOTE: You'll need to replace this url with your Firebase App's database
        // path in order for the database connection to work correctly in editor.
        app.SetEditorDatabaseUrl("https://frim-exam.firebaseio.com/");
        if (app.Options.DatabaseUrl != null)
            app.SetEditorDatabaseUrl(app.Options.DatabaseUrl);
        StartListener();
        isFirebaseInitialized = true;
    }

    void StartListener()
    {
        FirebaseDatabase.DefaultInstance
      .GetReference("Leaders")
      .GetValueAsync().ContinueWith(task => {
            if (task.IsFaulted)
            {
                // Handle the error...
            }
            else if (task.IsCompleted)
            {
                DataSnapshot snapshot = task.Result;
              // Do something with snapshot...
              Debug.Log("Done!");
              SceneManager.LoadSceneAsync("Scene2");
              Debug.Log("Done!!!");
          }
        });
    }
}

When I run this script, there are just show "Done!" log at the log console. The change scene script and below that, for example I want to write log "Done!!!" after the scene changed, is not executed.

Answer 1

why don't you use DontDestroyOnLoad for keeping the codes between different scene? Because The load of a new Scene destroys all current Scene objects. For this case could you try the belowing code of yours.

using Firebase;
using Firebase.Database;
using Firebase.Extensions;
using Firebase.Unity.Editor;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.SceneManagement;


private static bool created = false;

// the belowing code is used for changing the scene without losing the script
    void Awake()
    {
        if (!created)
        {
            DontDestroyOnLoad(this.gameObject);
            created = true;
            Debug.Log("Awake: " + this.gameObject);
        }
    }

public class NewBehaviourScript : MonoBehaviour
{
DependencyStatus dependencyStatus = DependencyStatus.UnavailableOther;
protected bool isFirebaseInitialized = false;
// Start is called before the first frame update
private void Start()
{

    FirebaseApp.CheckAndFixDependenciesAsync().ContinueWithOnMainThread(task => {
        dependencyStatus = task.Result;
        if (dependencyStatus == DependencyStatus.Available)
        {
            InitializeFirebase();
        }
        else
        {
            Debug.LogError(
              "Could not resolve all Firebase dependencies: " + dependencyStatus);
        }
    });
}
protected virtual void InitializeFirebase()
{
    FirebaseApp app = FirebaseApp.DefaultInstance;
    // NOTE: You'll need to replace this url with your Firebase App's database
    // path in order for the database connection to work correctly in editor.
    app.SetEditorDatabaseUrl("https://frim-exam.firebaseio.com/");
    if (app.Options.DatabaseUrl != null)
        app.SetEditorDatabaseUrl(app.Options.DatabaseUrl);
    StartListener();
    isFirebaseInitialized = true;
}

void StartListener()
{
    FirebaseDatabase.DefaultInstance
  .GetReference("Leaders")
  .GetValueAsync().ContinueWith(task => {
        if (task.IsFaulted)
        {
            // Handle the error...
        }
        else if (task.IsCompleted)
        {
            DataSnapshot snapshot = task.Result;
          // Do something with snapshot...
          Debug.Log("Done!");
          SceneManager.LoadSceneAsync("Scene2");
          Debug.Log("Done!!!");
      }
    });
}
}

Answer 2

So, the best answer is probably to just try to update to the latest version of the firebase SDK . The specific patch I'm thinking will help you is 6.5.0:

The instance of FirebaseApp, FirebaseAuth, FirebaseDatabase, FirebaseFunctions, FirebaseInstanceId and FirebaseStorage will be kept alive after creation until explicitly disposed.

So, as mentioned elsewhere, you probably just have to make sure scripts are marked as DontDestroyOnLoad(gameObject); , basically telling the entire game object (assuming it's at the scene root) that it shouldn't go away when its parent scene changes. For details and caveats see the Unity documentation .

There was also a change in the Firebase SDK that I think will help you out. When ever you call something like FirebaseApp.DefaultInstance , Firebase would do some amount of lazy initialization on that object. As in, first check if DefaultInstance is null. If it is, create it and return it out. This is a typical singleton pattern.

The change is that, for various reasons, this used to be a weak reference. As of 6.5.0, this was made into a normal C# reference (which means it's much less likely to get cleaned up), which may get rid of many bugs around "the scene changed, and something stopped working."

Barring that, just make sure you use DontDestroyOnLoad and make sure it's doing what you expect (ie: apply it to a game object at the root of the scene rather than a MonoBehaviour or a child object).

--Patrick

Answer 3

This is a classic Task continuation problem in Unity using Firebase. When you use, ContinueWith it is not ensured to be called on the main Unity thread. What you're trying to do SceneManager.LoadSceneAsync() requires to be executed on the Unity main thread. If you try to access GameObjects inside ContinueWith , even that will fail. The code just ghosts out without any error in the console.

The solution: Instead of ContinueWith , use ContinueWithOnMainThread from Firebase extensions which was made exactly for this reason.