使用活动之间的先前数据重新加载 recyclerView

Question

I created an app that has a Leaderboard it in.

The Leaderboard consists of 3 categories: Top rank, Most sharing, Most info.

In each category (tab), there is a recyclerView that loaded 25 results each from firestore .

What happens is that every time a user opens this activity it reads 75 documents which is pretty much and I'm trying to avoid it.

Is there any way that when a user starts the activity for the first time it will load these 75 documents but if he starts the activity 5 minutes later, for example, it will just display the same results as previously without reading 75 documents from firestore again?

Each recyclerView is loaded by using:

RecyclerView.LayoutManager mLayoutManager = new LinearLayoutManager( getApplicationContext() );
rv_TopRank.setLayoutManager( mLayoutManager );
rv_TopRank.setItemAnimator( new DefaultItemAnimator() );

private void showTopRanked() {
    usersID.clear();
    usersName.clear();
    usersResult.clear();

    db.collectionGroup( "UserData" ).orderBy( "rank", Query.Direction.DESCENDING ).limit( AppConstants.LEADERBOARD_TO_LOAD ).get()
            .addOnSuccessListener( queryDocumentSnapshots -> {
                for (QueryDocumentSnapshot document : queryDocumentSnapshots) {
                    if (document != null) {
                        usersID.add( document.getId() );
                        usersName.add( document.getString( "username" ) );
                        usersResult.add( document.getDouble( "rank" ) );
                    }
                }
                leaderBoardAdapter = new LeaderBoardAdapter( usersID, usersName, usersResult, 0 );
                rv_TopRank.setAdapter( leaderBoardAdapter );
                leaderBoardAdapter.notifyDataSetChanged();
            } );
}

Thank you

Answer 1

One option would be to use Android's Shared Preferences to save this data locally, and update it only when you deem it necessary as opposed to every time the app is opened.

Answer 2

You can use this approach:

In the onCreate() method of the activity, read the date from Calendar and save it in sharedPreferences as the date of last update and then check to see if the current date is not equal to the date of last update before you query from firebase.

Something like this:

val sharedPref = getSharedPreferences("SharedPref", Context.MODE_PRIVATE)

val today = Calendar.getInstance().get(Calendar.DAY_OF_YEAR)
val lastUpdateDay = sharedPref.getInt("lastUpdateDay", 0)

if (today != lastUpdateDay) {
    //THE LOCAL DATA IS OLD SO IT NEEDS TO BE UPDATED FROM FIREBASE THEREFORE:
   
    //Query and show Firebase database data
    //Store the data locally (Either in a database or again in sharedPref)
    //and save `today` to sharedPref in the onSuccess() block like so:
    sharedPref.edit().putInt("lastUpdateDay", today).apply()
} else {
    //THE LOCAL DATA IS UP-TO-DATE SO NO NEED FOR A FIREBASE QUERY

    //Load the data you have stored locally the day before
}

I'm sorry the code is in Kotlin. it's just to give you an idea.