Android RoomDatabase with ViewModel and Coroutines

Yogendra singh

1 April 2019

Coroutine:

coroutines are light-weight threads. They are launched with launch coroutine builder in a context of some CoroutineScope. A coroutine is a method that executes for a certain period, suspends, and permits other coroutines to run.

Use Cases:

The common use cases for coroutines on Android would be fetching data from the network, parsing large JSON datasets, writing data to a database. Therefore, calling code like this from the main thread can cause the app to pause, stutter, or even freeze. And if you block the main thread for too long, the app may even crash and present an Application Not Responding dialog.

Add dependenceis:

To get started with coroutines on Android you will need to add coroutine and following dependencies.

//Coroutines
implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-core:1.1.1'
implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-android:1.1.1'

//Live data and life cycles
implementation 'androidx.lifecycle:lifecycle-extensions:2.0.0'
implementation 'androidx.lifecycle:lifecycle-viewmodel-ktx:2.0.0'
implementation 'androidx.lifecycle:lifecycle-livedata:2.0.0'

//Coroutines

implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-core:1.1.1'

implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-android:1.1.1'

//Live data and life cycles

implementation 'androidx.lifecycle:lifecycle-extensions:2.0.0'

implementation 'androidx.lifecycle:lifecycle-viewmodel-ktx:2.0.0'

implementation 'androidx.lifecycle:lifecycle-livedata:2.0.0'

Database Call using coroutines

We have ViewModel with some LiveData objects that the Activity will be able to observe added. Add a coroutine scope to MainViewModel. In Kotlin, all coroutines run inside a CoroutineScope.A scope controls the lifetime of coroutines through its job.

import androidx.annotation.UiThread
import androidx.lifecycle.LiveData
import androidx.lifecycle.MutableLiveData
import androidx.lifecycle.ViewModel
import com.webkul.remindme.android.model.ScheduleReminderData
import com.webkul.remindme.android.roomdb.DataBaseManager 
import kotlinx.coroutines.*

class MainViewModel : ViewModel() {
    private val _scheduleReminderData = MutableLiveData<List<ScheduleReminderData>>()
    @UiThread
    fun loadScheduleReminderData(): LiveData<List<ScheduleReminderData>> {
        ioMain({
            DataBaseManager .getScheduleReminderData()
        }) {
            _scheduleReminderData.value = it
        }
        return _scheduleReminderData
    }

    fun <T : Any> ioMain(
        work: suspend (() -> T?),
        callback: ((T?) -> Unit)? = null
    ): Job =
        CoroutineScope(Dispatchers.Main).launch {
            val data = CoroutineScope(Dispatchers.IO).async {
                return@async work()
            }.await()

            callback?.let {
                it(data)
            }
        }
}

import androidx.annotation.UiThread

import androidx.lifecycle.LiveData

import androidx.lifecycle.MutableLiveData

import androidx.lifecycle.ViewModel

import com.webkul.remindme.android.model.ScheduleReminderData

import com.webkul.remindme.android.roomdb.DataBaseManager

import kotlinx.coroutines.*

class MainViewModel : ViewModel() {

private val _scheduleReminderData = MutableLiveData<List<ScheduleReminderData>>()

@UiThread

fun loadScheduleReminderData(): LiveData<List<ScheduleReminderData>> {

ioMain({

DataBaseManager .getScheduleReminderData()

}) {

_scheduleReminderData.value = it

}

return _scheduleReminderData

}

fun <T : Any> ioMain(

work: suspend (() -> T?),

callback: ((T?) -> Unit)? = null

): Job =

CoroutineScope(Dispatchers.Main).launch {

val data = CoroutineScope(Dispatchers.IO).async {

return@async work()

}.await()

callback?.let {

it(data)

}

import androidx.annotation.WorkerThread
import androidx.room.Database
import androidx.room.Room
import androidx.room.RoomDatabase
import com.webkul.remindme.android.ReminderApplication
import com.webkul.remindme.android.model.ScheduleReminderData
import com.webkul.remindme.android.model.ScheduleRemindersData

@Database(entities = [ScheduleReminderData::class], version = 1, exportSchema = false)
abstract class ScheduleReminderDataDatabase : RoomDatabase() {
    abstract fun scheduleRemindersData(): ScheduleRemindersData

    companion object {
        private var INSTANCE: ScheduleReminderDataDatabase? = null
        @WorkerThread
        fun get(): ScheduleReminderDataDatabase {
            if (INSTANCE == null) {
                INSTANCE = Room
                    .inMemoryDatabaseBuilder(
                        ReminderApplication.applicationContext(),
                        ScheduleReminderDataDatabase::class.java
                    )
                    .fallbackToDestructiveMigration()
                    .build()
            }
            return INSTANCE!!
        }
    }
}

import androidx.annotation.WorkerThread

import androidx.room.Database

import androidx.room.Room

import androidx.room.RoomDatabase

import com.webkul.remindme.android.ReminderApplication

import com.webkul.remindme.android.model.ScheduleReminderData

import com.webkul.remindme.android.model.ScheduleRemindersData

@Database(entities = [ScheduleReminderData::class], version = 1, exportSchema = false)

abstract class ScheduleReminderDataDatabase : RoomDatabase() {

abstract fun scheduleRemindersData(): ScheduleRemindersData

companion object {

private var INSTANCE: ScheduleReminderDataDatabase? = null

@WorkerThread

fun get(): ScheduleReminderDataDatabase {

if (INSTANCE == null) {

INSTANCE = Room

.inMemoryDatabaseBuilder(

ReminderApplication.applicationContext(),

ScheduleReminderDataDatabase::class.java

)

.fallbackToDestructiveMigration()

.build()

}

return INSTANCE!!

}

@Dao
interface ScheduleRemindersData {
    @Query("SELECT * FROM ScheduleReminderData")
    fun getAll(): List<ScheduleReminderData>
}

@Dao

interface ScheduleRemindersData {

@Query("SELECT * FROM ScheduleReminderData")

fun getAll(): List<ScheduleReminderData>

}

import android.os.Bundle
import android.util.Log
import androidx.databinding.DataBindingUtil
import androidx.lifecycle.Observer
import androidx.lifecycle.ViewModelProviders
import androidx.recyclerview.widget.RecyclerView
import com.webkul.remindme.android.BR
import com.webkul.remindme.android.R
import com.webkul.remindme.android.adapter.RemindersRvdapter
import com.webkul.remindme.android.databinding.ActivityMainBinding
import com.webkul.remindme.android.handler.MainActivityHandler
import com.webkul.remindme.android.model.MainViewModel

class MainActivity : BaseActivity() {
     val mViewModel by lazy {
        ViewModelProviders.of(this).get(MainViewModel::class.java)
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
       
 mViewModel.loadScheduleReminderData().observe(this, Observer {
            // use it
                 })
    }   
}

import android.os.Bundle

import android.util.Log

import androidx.databinding.DataBindingUtil

import androidx.lifecycle.Observer

import androidx.lifecycle.ViewModelProviders

import androidx.recyclerview.widget.RecyclerView

import com.webkul.remindme.android.BR

import com.webkul.remindme.android.R

import com.webkul.remindme.android.adapter.RemindersRvdapter

import com.webkul.remindme.android.databinding.ActivityMainBinding

import com.webkul.remindme.android.handler.MainActivityHandler

import com.webkul.remindme.android.model.MainViewModel

class MainActivity : BaseActivity() {

val mViewModel by lazy {

ViewModelProviders.of(this).get(MainViewModel::class.java)

}

override fun onCreate(savedInstanceState: Bundle?) {

super.onCreate(savedInstanceState)

mViewModel.loadScheduleReminderData().observe(this, Observer {

// use it

})

}