Firebase keepsynced

问题

Working with Firebase in a Unity project, for a simple highscore, I stumbled on problems when doing a query. In editor, everything works like a charm (Editor does not have persistence) On devices (with persistence enabled) the troubles begin. Query is showing cached Firebase data, so it is only correct on first ever call in the client, and then when Firebase sees it fit to sync (maybe never, since there is no eventhandler)

However, looking for a solution, there is no way to force an update of the cached values. I then tested with KeepSynced(true) on the query and this seems to work:

this.HiscoreQuery = hiscoreref.OrderByChild ("Score").LimitToLast (20);
this.HiscoreQuery.KeepSynced(true);
this.HiscoreQuery.GetValueAsync().ContinueWith (task => {
  if (task.IsFaulted) {
    Debug.LogError ("Get hiscores faulted");
    return;
  }
  if (task.Result != null && task.Result.ChildrenCount > 0) {
    Debug.Log ("Get hiscore data success!");
    this.AddDelayedUpdateAction (() => this.OnGetHiScores (task.Result));
  }
});

Question: While this can be fine if Firebase only listen for the Query's LImitToLast(20), it would be a very bad thing, if the Firebase internally is keeping the whole (growing) hiscorelist copied in every client.

Does anyone know if KeepSynced(true) is limited to the actual query scope or the whole tree/branch? And how could one validate this?

回答1:

GetValue calls don't work well with KeepSynced(true). Firebase eagerly returns you the value from the cache, and only then loads the data from the server.

For a longer explanation, see my answer here: Firebase Offline Capabilities and addListenerForSingleValueEvent

If you want to use caching, use listeners and not GetValue calls. With a listener, your callback will be fired twice (if there is a change): once with the value from the cache, and then once with the value from the server.

来源：https://stackoverflow.com/questions/59777235/firebase-keepsynced