Question How to wait for a database result?

Hello everyone,

I guess I have a rather standard issue, but I do not figure out how to solve it.

The szenario is a racing game where at the moment the finish line is reached the following things shall happen:

1. Load previous highscores from the database
2. Do some magical calculation (check if new top highscore, etc.)
3. Save the new highscore list to the database
   

The problem I am facing right now is that 2 and 3 is done before I got the result from 1, hence I do not have the stored highscores yet before the rest is done.

So at the end I "simply" looking for a way to wait until loading the database is finished.

I tried different approaches with Coroutines and "yield return new WaitUntil" but non of it worked.

Here are the relevant parts of my code:

Class: HighscoreController

Code (CSharp):

1.  
2. public void AddHighScore(string playerName, float time)
3.      {
4.          currentPlayerHighscore = new PlayerHighscore(playerName, time);
5.          //LoadHighscores();
6.          highscoresDB = FirebaseManagerGame.instance.LoadHighscoresOfLevel(levelInfo.LevelName);
7.          Debug.LogWarning("HERE I HAVE TO WAIT UNTIL DATABASE RESULT IS THERE");
8.          //reset values
9.          newTopHighscore = false; inTop10 = false; notInTop10 = false;
10.         [...] some magical calculation [...]
11.          highscoresDB.Sort(SortByTime);
12.    
13.          SaveHighscoresDB();
14.          ShowHighScores();
15.      }

Class: FirebaseManagerGame

Code (CSharp):

1.  
2.  
3. public List<PlayerHighscore> LoadHighscoresOfLevel(string levelName)
4.      {
5.          Debug.Log("FireBaseGame - LoadHighscoresOfLevel START");
6.          List<PlayerHighscore> tmpList = new List<PlayerHighscore>();
7.          StartCoroutine(GetHighscoresOfLevel(levelName, returnValue =>
8.          {
9.              tmpList = returnValue;
10.          }));
11.          Debug.Log("LoadHighscoresOfLevel List.count: " + tmpList.Count);
12.          return tmpList;
13.      }
14.  
15.  
16.      private IEnumerator GetHighscoresOfLevel(string levelName, System.Action<List<PlayerHighscore>> callback)
17.      {
18.          Debug.Log("FireBaseGame - getHighscoresOfLevel START");  
19.          List<PlayerHighscore> tmpHighscores = new List<PlayerHighscore>();          
20.          Task<DataSnapshot> DBTask = DBreference.Child("levelHighscores").Child(levelName).GetValueAsync();
21.          yield return new WaitUntil(predicate: () => DBTask.IsCompleted);
22.          if (DBTask.Exception != null)
23.          {
24.              Debug.LogWarning(message: $"Failed to register task with {DBTask.Exception}");
25.          }
26.          else if (DBTask.Result.Value == null) //No data exists yet
27.          {
28.              Debug.Log("getHighscoresOfLevel - NO DATA EXISTS");
29.          }
30.          else //Data has been retrieved
31.          {
32.              DataSnapshot snapshot = DBTask.Result;
33.              tmpHighscores = JsonConvert.DeserializeObject<List<PlayerHighscore>>(snapshot.GetRawJsonValue());
34.              Debug.Log("getHighscoresOfLevel - FOUND DATA - count: " + tmpHighscores.Count);
35.              callback(tmpHighscores);
36.          }
37.      }

I hope you can help me to solve this issue.

Thanks in advance!

oetzi

 

Here is the solution. The magic trick are 2 words: "yield return" which cause the method to wait until the database results returned. To be able to use these magic words I had to change the AddHighScore method into an IEnumerator.

Code (CSharp):

1. public IEnumerator AddHighScore(string playerName, float time)
2. {
3.      currentPlayerHighscore = new PlayerHighscore(playerName, time);
4.      //IEnumerator cannot return any internal values / variables. Hence, the following way can be used:
5.      //pass a place holder (= returnValue) to the IEnumerator. Within the IEnumerator this placeholder can be set to any value. Outside the Enumerator / here it can be further processed.
6.      yield return StartCoroutine(FirebaseManagerGame.instance.GetHighscoresOfLevel(levelInfo.LevelName, returnValue =>
7.      {
8.          highscoresDB = returnValue;
9.      }));
10. [...]