Develop Reference

Android Firebase - Local Cached Data

It is about Firebase's local cached data in Android.
If the Android user, has 1-2 years data in Firebase,
is there a way to enable, setup, or filter Firebase persistence in local,
so that it only create local cache for the last month ?
So we don't the whole data in local cache, but only the last month.

The Firebase local cache is not designed to be manually populated. It's managed automatically, and you don't have much control over what gets stored in it. It will store data from recent queries, and it will evict data that hasn't been used. You can't choose which data will or will not be cached - it work with everything or nothing at all.
The local cache is meant to be helpful when the user temporarily loses their network connection. It's not meant for full offline support.
If you need a cache for very specific data that you can control, you will need to build that yourself.

Firebase offline capabilities causing memory problems

I am developing a chat app that uses firebase database to store data. The usual approach while developing a chat app is to keep the database nodes synced so that you access the messages offline. So the problem rises when I implement the firebase offline capabilities to keep the data nodes synced. Firebase suggests two required steps for accessing data offline:
Enabling disk persistance
this is enabled according to the documentation by using this line of code (in my case I add it in application class):
FirebaseDatabase.getInstance().setPersistanceEnabled(true);
and
Keeping a node synced
this is enabled by simply adding keepsynced(true) to any databasereference that you wish to keep synced, like this:
ChatNode.keepSynced(true);
What is the difference between the two?
According to the firebase team answers on this site, I deduced that:
1) (Disk persistance) stores the data on the device disk to use them when needed, and data is stored wether you write data or read data.
a) If you write data offline: data is stored on disk and is sent to database when you go online again.
b) If you read data offline: the listener that was read online and was kept in disk and stored, you will be able to read it offline from disk.
2) (keep synced true) will keep a database reference synced in 2 ways:
a) If you are also using (disk persistence) with (keep synced) you will be able to keep data synced on disk ... which seems to be the default behavior of (disk persistence).
b) If you are using (keep synced) alone then you only store to what is known as the app memory.
The problem
I did set both of the methods, but my app is now very laggy and slow and sometimes stops on its own.
The question
If all the things that I said above are true, then would this method of offline capability be a heavy load on my app?
If I kept many listeners synced and set persistence enabled, then would the disk become full of data? Should I clean the data? Is the data on disk cleaned by itself in both methods? Is data cleaned by itself from memory?
I want to avoid the lagging and slow response in my app, thanks for your help.

You are right about your assumptions. If you are using FirebaseDatabase.getInstance().setPersistenceEnabled(true); means that Firebase will create a local copy of your database which also means that every change that is made while you are offline, will be added to a queue. So, as this queue grows, local operations and application startup will slow down. So the speed depends on the dimension of that queue. But rememeber, Firebase is designed as an online database that can work for short to intermediate periods of being disconnected and not as an offline database.
Second, if are using many listeners, don't forget to remove the listener accordingly to the life-cycle of your activity like this:
databaseReference.removeEventListener(valueEventListener);

Firebase how to detect if cached data is available

I have an application that pulls some simple data from Firebase Realtime Database, and to make things simple here is the flow that I want to have.
If phone is connected to the internet:
Get the data from the firebase database
If phone is offline
If there is data in firebase cache -> get data from cache
If there is nothing in firebase cache -> show some default data stored locally in app
The problem is that I don't see possible way to detect if data is available in firebase cache. So when phone is offline I cannot see if I should display the locally stored data or cache from firebase database.

Agree above answer, Firebase will do it for you, if you do it in the right way. In order to solve your problem, you should understand the difference between the two approaches of firebase offline cache - reading-from-memory and reading-from-disk.
Read this article -> https://pamartinezandres.com/lessons-learnt-the-hard-way-using-firebase-realtime-database-c609b52b9afb
in your case, just add, FirebaseDatabase.getInstance().setPersistenceEnabled(true); to enable reading from disk
and add yourReferenceForFirebase.keepSynced(true); to keep the data synched
then your app will work as you expected.
But, only this part: "If there is nothing in firebase cache -> show some default data stored locally in app", seems impossible.

Firebase does it for you.
Firebase applications work even if your app temporarily loses its network connection.
Also firebase apps automatically handle temporary network interruptions.
Cached data is available while offline and Firebase resends any writes when network connectivity is restored.
If it is not enough and you need to work offline you can also enable the disk persistence just adding:
FirebaseDatabase.getInstance().setPersistenceEnabled(true);
More info here.
EDIT:
There is no way to know whether a value comes from the local cache or from the remote server.
There is only a way to know if your app is currently connected to the Firebase Database server.
To achieve it you can detect the connection state by listening for the .info/connected value.

Firebase Database offline writing

In my Android app I have to keep an existing SQLite database, but in order to sync elements (tasks from a todo-list) to multiple devices I decided to use Firebase Database.
So I'm not enabling Firebase Database offline mode, since I have to use SQLite for that (it's for a college project).
So what I'm doing for writes is that, whenever some data gets added or removed from the local SQLite database that change is also made to the Firebase one.
All this works as expected if the user is connected to the Internet, or even if the user adds a task offline and then becomes online while being on the app.
But if the user adds a task offline, then closes the app and then becomes online in another app, the change doesn't get pushed to the database, even if the user opens my app again.
Any ideas?
Thank you.

As you did not enable the Firebase Database offline mode all data your app trying to push are not saved in persistent storage, only in memory. Thats why all these data are not pushed to Firebase after application restart.
So you need some synchronization algorithm at application startup which pushes data from you local database to firebase (and vise versa).
For example, you can use timestamp marker (System.currentTimeMillis()) in both local and firebase side which always should be updated on any database change.
Then at application startup you can just check this marker:
if local marker is greater than the remote one - that means that
remote database is outdated. So just copy all your local sql database
data to firebase.
if remote marker is greater than the local one - just clean local db
and download all data from firebase.
if both markers are equal - that means that everything is up to date,
do nothing.
Hope this helps :)

Firebase' true offline capabilities

I'm trying to find out how far the offline capabilities of Firebase on Android actually go.
As far as I understand, it should be possible to make the Database "persistent" with FirebaseDatabase.getInstance().setPersistenceEnabled(true);
The documentation reads:
The Firebase Realtime Database stores data returned from a query for use when offline. For queries constructed while offline, the Firebase Realtime Database continues to work for previously loaded data. If the requested data hasn't loaded, the Firebase Realtime Database loads data from the local cache. When we come back online our data will load and reflect the query.
Is this also true when the offline state is beeing forced by goOffline?
In this question the user got an answer from firebase support:
While you can use goOffline() to force the client offline for a long time, performance will deteriorate over time. The Firebase clients will queue intermediate state changes, instead of updating the stored state as the server does.
Does this mean the "local database" isn't actually updated like it would be when offline due to connection loss?
Because most of the time any query or value event listener doesn't come back, onDataChange is never called as is onCanceled (I checked!)
If only the connection is lost, it actually works as advertised, although sometimes with up to a minute delay, which seems to be a problem on its own.
What is then the intention of even offering the goOffline() method if this just stops the interaction with the database completely?
In my implementation the app starts offline, with an anonymous authentication. So in the beginning of course the "local database" will be completely empty. But shouldn't the value events at least fire onDataChanged with an empty datasnapshot?
I tried staying online until I received the anonymous UID and added an empty entry into firebase database, which then is queried/cached. After that if I call goOffline, no more entries can be added and no more queries will be answered.
Similar to the above mentioned question, my plan is to offer the user the option to stay offline, with of course the downside of the build up of stored write events in the local cache (but that shouldn't be that big of a problem as there isn't that much data)
So how can I make this work if even possible at all?
The only thing I can see is to have some different database solution in the beginning for actual offline capabilities which has to be translated & transferred to firebase when the user chooses to go online.