pocketcommunityclient/app/src/main/java/com/community/pocket/util/AppDatabase.java

package com.community.pocket.util;

import android.content.Context;

import androidx.lifecycle.LiveData;
import androidx.lifecycle.MutableLiveData;
import androidx.room.Database;
import androidx.room.Room;
import androidx.room.RoomDatabase;

import com.community.pocket.data.dao.TokenDao;
import com.community.pocket.data.model.Token;

@Database(entities = {Token.class}, version = 1, exportSchema = false)
public abstract class AppDatabase extends RoomDatabase {
    public abstract TokenDao tokenDao();

    private static AppDatabase sInstance;

    public static final String DATABASE_NAME = "basic-sample-db";

    private final MutableLiveData<Boolean> mIsDatabaseCreated = new MutableLiveData<>();

    public static AppDatabase getInstance(Context context) {
        if (sInstance == null) {
            synchronized (AppDatabase.class) {
                if (sInstance == null) {
                    sInstance = buildDatabase(context.getApplicationContext());
                    sInstance.updateDatabaseCreated(context.getApplicationContext());
                }
            }
        }
        return sInstance;
    }

    /**
     * Build the database. {@link Builder#build()} only sets up the database configuration and
     * creates a new instance of the database.
     * The SQLite database is only created when it's accessed for the first time.
     */
    private static AppDatabase buildDatabase(Context appContext) {
        return Room.databaseBuilder(appContext, AppDatabase.class, DATABASE_NAME)
                .build();
    }

    /**
     * Check whether the database already exists and expose it via {@link #getDatabaseCreated()}
     */
    private void updateDatabaseCreated(final Context context) {
        if (context.getDatabasePath(DATABASE_NAME).exists()) {
            setDatabaseCreated();
        }
    }

    private void setDatabaseCreated() {
        mIsDatabaseCreated.postValue(true);
    }

    public LiveData<Boolean> getDatabaseCreated() {
        return mIsDatabaseCreated;
    }
}