RecyclerView के साथ कक्ष डेटाबेस दृश्य

मैं रूम और कोटलिन के लिए नया हूं, और मैं एक साधारण रूम का डेटाबेस बनाने और इसे एक रीसाइक्लर व्यू में प्रस्तुत करने की कोशिश कर रहा हूं जो व्यूपेजर में बैठता है।

गतिविधि में एक ViewPager ऑब्जेक्ट होता है, जिसमें ViewPager में एक Fragment होता है, और उस Fragment में एक RecyclerView होता है: गतिविधि -> ViewPager -> Fragment -> RecyclerView

मेरे पास समस्या यह है कि जब मैं डेटाबेस प्राप्त करने का प्रयास कर रहा हूं (एक प्रविष्टि के बाद) मैं शून्य हो जाता हूं।

कोड:

@Entity(tableName = "Guests_table")
data class Guest(@NonNull @ColumnInfo (name = "Name") var name: String,
             @ColumnInfo (name = "Phone number") var phoneNumber: String,
             @ColumnInfo (name = "Coming") var coming: Boolean = false,
             @ColumnInfo (name = "Participants") var participants: Int)
{
@PrimaryKey (autoGenerate = true)
var id: Long = 0

init
{
    phoneNumber = PhoneNumberUtils.formatNumber(phoneNumber, Locale.getDefault().country)
}
}

डीएओ:

@Dao
interface GuestsDAO
{
    @Insert
    fun insert(guest: Guest)

    @Delete
    fun delete(guest: Guest)

    @Query ("DELETE FROM Guests_table")
    fun deleteAll()

    @Query ("SELECT * FROM Guests_table ORDER BY name ASC")
    fun getAllGuests(): List<Guest>
}

डेटाबेस:

@Database(entities = [Guest::class], version = 1)
abstract class InviterRoomDatabase: RoomDatabase()
{
    abstract fun guestsDao(): GuestsDAO

    companion object
    {
        private var INSTANCE: InviterRoomDatabase ?= null

        fun getDatabase(context: Context): InviterRoomDatabase?
        {
            if (INSTANCE == null)
            {
                synchronized(InviterRoomDatabase::class)
                {
                    INSTANCE = Room.databaseBuilder(context.applicationContext,InviterRoomDatabase::class.java,"Guests.db").build()
                }
            }

            return INSTANCE
        }

        fun destroyInstance()
        {
            INSTANCE = null
        }
    }
}

गतिविधि:

class EventActivity : AppCompatActivity()
{
    private lateinit var viewPager: ViewPager

    override fun onCreate(savedInstanceState: Bundle?)
    {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_event)

        viewPager = findViewById(R.id.guests_view_pager)
        val pagerAdapter =  EventPagerAdapter(supportFragmentManager)
        viewPager.adapter = pagerAdapter
    }
}

अनुकूलक:

class EventPagerAdapter(fragmentManager: FragmentManager): FragmentPagerAdapter(fragmentManager)
{

    override fun getCount(): Int
    {
        return 1
    }

    override fun getItem(position: Int): Fragment
    {
        return GuestListFragment.newInstance()
    }
}

टुकड़ा:

class GuestListFragment : Fragment()
{
    private var guestsDataBase: InviterRoomDatabase? = null
    private lateinit var dbWorkerThread: DBWorkerThread

    companion object
    {
        fun newInstance(): GuestListFragment
        {
            val fragment = GuestListFragment()
            return fragment
        }
    }


    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? 
    {

        dbWorkerThread = DBWorkerThread("workerThread")
        dbWorkerThread.start()
        guestsDataBase = InviterRoomDatabase.getDatabase(this.context!!)
        insertGuestToDB(Guest("Joe","052352332",false,0))

        var rootView = inflater.inflate(R.layout.fragment_guest_list, container, false)
        var rv: RecyclerView = rootView.findViewById(R.id.guests_list_recycler_view)
        rv.layoutManager = LinearLayoutManager(context)

        var d = getAllDataFromDB()
        rv.adapter = GuestsRecycleViewAdapter.newInstance(d)

        return rootView
    }


    private fun insertGuestToDB(guest: Guest)
    {
        val task = Runnable {guestsDataBase?.guestsDao()?.insert(guest)}
        dbWorkerThread.postTask(task)
    }

    private fun getAllDataFromDB(): List<Guest>
    {
        var data: List<Guest> = emptyList()
        val task = Runnable { data = guestsDataBase?.guestsDao()?.getAllGuests()!!}

        dbWorkerThread.postTask(task)

        return data
    }
}