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Sort recycler view by using room database

I wanna create a menu about sorting by Task's attributes but don't know how because I am using database combined with Live Data, View Model and coroutine which is very complicated. Please show me how to handle these logics.
Data file
#Entity(tableName = "task_table")
data class Task(
//id is the PrimaryKey which is auto generated by Android Room Database
#PrimaryKey(autoGenerate = true)
val id: Int,
val date: String,
val content: String,
var timeLeft: String,
var isDone: Boolean
):Parcelable
Dao file
#Dao
interface TaskDao {
// means it will be just ignore if there is a new exactly same task then we're gonna just ignore it
#Insert(onConflict = OnConflictStrategy.IGNORE)
suspend fun addTask(task: Task)
#Delete
suspend fun deleteTask(task: Task)
#Update
suspend fun updateTask(task: Task)
#Query("SELECT * FROM task_table order by timeLeft ASC")
fun readAllData(): LiveData<MutableList<Task>>
#Query("SELECT COUNT(id) FROM task_table")
fun getCount(): Int
}
Database file
#Database(entities = [Task::class], version = 1, exportSchema = false)
abstract class TaskDatabase : RoomDatabase() {
abstract fun taskDao(): TaskDao
companion object {
#Volatile
private var INSTANCE: TaskDatabase? = null
fun getDatabase(context: Context): TaskDatabase {
val tempInstance = INSTANCE
if (tempInstance != null) {
return tempInstance
}
synchronized(this)
{
val instance = Room.databaseBuilder(
context.applicationContext,
TaskDatabase::class.java,
"task_database"
).build()
INSTANCE = instance
return instance
}
}
}
}
Repository file
// a repository class abstracts access to multiple data sources
class TaskRepository(private val taskDao: TaskDao) {
val readAllData: LiveData<MutableList<Task>> = taskDao.readAllData()
suspend fun addTask(task: Task) {
taskDao.addTask(task)
}
suspend fun deleteTask(task: Task) {
taskDao.deleteTask(task)
}
suspend fun updateTask(task: Task) {
taskDao.updateTask(task)
}
}
ViewModel file
class TaskViewModel(application: Application) : AndroidViewModel(application) {
val readAllData: LiveData<MutableList<Task>>
private val repository: TaskRepository
init {
val taskDao = TaskDatabase.getDatabase(application).taskDao()
repository = TaskRepository(taskDao)
readAllData = repository.readAllData
}
fun addTask(task: Task) {
viewModelScope.launch(Dispatchers.IO) {
repository.addTask(task)
}
}
fun updateTask(task: Task) {
viewModelScope.launch(Dispatchers.IO) {
repository.updateTask(task)
}
}
fun deleteTask(task: Task) {
viewModelScope.launch(Dispatchers.IO) {
repository.deleteTask(task)
}
}
}
In my fragment these will be a menu to choose how recyclerview items should be sorted. Don't know how to handle these logic. Please help. I appreciate!

How can i get one item from Room database?

So, I have two ViewModels and two screens in my app. The first screen is for the presentation of a list of diary item elements, second is for detailed information on diary items. In a second ViewModel, I have an id to get a record from DB but can find it. What can I do to get it?
DAO:
interface DiaryDao {
#Query("SELECT * FROM diaryItems")
fun getAllDiaryPosts(): LiveData<List<DiaryItem>>
#Query("Select * from diaryItems where id = :id")
fun getDiaryPostById(id: Int) : DiaryItem
#Query("Delete from diaryItems where id = :index")
fun deleteDiaryPostByIndex(index : Int)
#Insert(onConflict = OnConflictStrategy.REPLACE)
suspend fun insertDiaryPost(diaryItem: DiaryItem)
#Update
suspend fun updateDiaryPost(diaryItem: DiaryItem)
#Delete
suspend fun deleteDiaryPost(diaryItem: DiaryItem)
#Query("Delete from diaryItems")
suspend fun deleteAllDiaryItems()
}
Repository
class DiaryRepository #Inject constructor(private val diaryDao: DiaryDao) {
val readAllData: LiveData<List<DiaryItem>> = diaryDao.getAllDiaryPosts()
suspend fun getDiaryPostDyIndex(index: Int): DiaryItem {
return diaryDao.getDiaryPostById(index)
}
}
First viewmodel
#HiltViewModel
class PostListViewModel
#Inject
constructor(
private val diaryRepository: DiaryRepository,
) : ViewModel() {
private var allDiaryItems: LiveData<List<DiaryItem>> = diaryRepository.readAllData
}
Second viewmodel
#HiltViewModel
class PostDetailViewModel
#Inject
constructor(
private val savedStateHandle: SavedStateHandle,
private val diaryRepository: DiaryRepository
) : ViewModel() {
sealed class UIState {
object Loading: UIState()
data class Success(val currentPosts: DiaryItem) : UIState()
object Error : UIState()
}
val postDetailState: State<UIState>
get() = _postDetailState
private val _postDetailState = mutableStateOf<UIState>(UIState.Loading)
init {
viewModelScope.launch (Dispatchers.IO) {
try {
val diaryList: DiaryItem = diaryRepository.getDiaryPostDyIndex(2) //it is for test
_postDetailState.value = UIState.Success(diaryList)
} catch (e: Exception) {
withContext(Dispatchers.Main) {
_postDetailState.value = UIState.Error
}
}
}
}
}

I am sure you are getting errors. because you updating UI State in IO Thread
fun getDairyItem(itemId: Int){
viewModelScope.launch (Dispatchers.IO) {
try {
val diaryList: DiaryItem = diaryRepository.getDiaryPostDyIndex(itemId)
withContext(Dispatchers.Main) {
_postDetailState.value = UIState.Success(diaryList)
}
} catch (e: Exception) {
withContext(Dispatchers.Main) {
_postDetailState.value = UIState.Error
}
}
}
}

Receiving null in observed livedata instead of object

I am not sure what is exactly happening but when ApiService.apiService.getPokemon(name) in fun getPokemon in PokemonRepository.kt is called then the function getPokemon stops executing and emited livedata are then observed as null in DetailAktivity.kt instead of a valid Pokemon class.
I have checked the API call and it is working in other cases. I am new to Android programming, so I would appreciate some detailed explanation.
Here are the classes:
PokemonRepository.kt
class PokemonRepository(context: Context) {
companion object {
private val TAG = PokemonRepository::class.java.simpleName
}
private val pekemonDao = PokemonDatabase.getInstance(context).pokemonDao()
fun getPokemon(name: String) = liveData {
val disposable = emitSource(
pekemonDao.getOne(name).map {
it
}
)
val pokemon = ApiService.apiService.getPokemon(name)
try {
disposable.dispose()
pekemonDao.insertAllPokemons(pokemon)
pekemonDao.getOne(name).map {
it
}
} catch (e: Exception) {
Log.e(TAG, "Getting data from the Internet failed", e)
pekemonDao.getOne(name).map {
e
}
}
}
DetailActivity.kt
class DetailActivity : AppCompatActivity() {
companion object {
const val ITEM = "item"
}
private lateinit var binding: ActivityDetailBinding
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = ActivityDetailBinding.inflate(layoutInflater)
setContentView(binding.root)
val vm: DetailViewModel by viewModels()
vm.pokemon.observe(
this,
{
binding.name.text = it.name
supportActionBar?.apply {
setDisplayShowTitleEnabled(true)
title = it.name
}
}
)
intent.extras?.apply {
vm.setCharacterId(getString(ITEM)!!)
}
}
}
DetailViewModel
class DetailViewModel(application: Application) : AndroidViewModel(application) {
private val repository = PokemonRepository(application)
private val name: MutableLiveData<String> = MutableLiveData()
val pokemon = name.switchMap { name ->
repository.getPokemon(name)
}
fun setCharacterId(characterId: String) {
name.value = characterId
}
}
ApiService.kt
interface ApiService {
#GET("pokemon?offset=0&limit=151")
suspend fun getPokemons(#Query("page") page: Int): NamedApiResourceList
#GET("pokemon/{name}")
suspend fun getPokemon(#Path("name") name: String): Pokemon
companion object {
private const val API_ENDPOINT = "https://pokeapi.co/api/v2/"
val apiService by lazy { create() }
private fun create(): ApiService = Retrofit.Builder()
.baseUrl(API_ENDPOINT)
.addConverterFactory(MoshiConverterFactory.create())
.client(OkHttpClient())
.build()
.create(ApiService::class.java)
}
}
Pokemon data class
#Parcelize
#JsonClass(generateAdapter = true)
#Entity
data class Pokemon(
#PrimaryKey val id: Int,
val name: String,
#ColumnInfo(name = "base_experience") val baseExperience: Int,
val height: Int,
#ColumnInfo(name = "is_default") val isDefault: Boolean,
val order: Int,
val weight: Int,
val sprites: PokemonSprites,
) : Parcelable
PokemonDao.kt
#Dao
interface PokemonDao {
#Query("SELECT * FROM namedapiresource")
fun getAll(): LiveData<List<NamedApiResource>>
#Query("SELECT * FROM pokemon WHERE name=:name")
fun getOne(name: String): LiveData<Pokemon>
#Insert(onConflict = OnConflictStrategy.IGNORE)
suspend fun insertAllNamedApiResources(vararg characters: NamedApiResource)
#Insert(onConflict = OnConflictStrategy.IGNORE)
suspend fun insertAllPokemons(vararg characters: Pokemon)
}

I would guess because of how your getPokemon is defined:
val disposable = emitSource(
// Attempts to get a pokemon from the database - presumably this does
// not exist at first so would return null first
pekemonDao.getOne(name).map {
it
}
)
// AFTER NULL IS RETURNED this tries to fetch from the API
val pokemon = ApiService.apiService.getPokemon(name)
try {
disposable.dispose()
pekemonDao.insertAllPokemons(pokemon)
// After fetching from API, finally returns a non-null
pekemonDao.getOne(name).map {
it
}
So maybe just get ride of the initial block?
val disposable = emitSource(
pekemonDao.getOne(name).map {
it
}
)

No record save in room database

After inserting data into RoomDB when I fetch it using mindValleyDao.getCategories().value It returns null
DatabaseClass
#Database(entities = arrayOf(CategoryBO::class), version = 1, exportSchema = false)
abstract class MindValleyDatabase : RoomDatabase(){
abstract fun mindValleyDao(): MindValleyDao
companion object {
// Singleton prevents multiple instances of database opening at the
// same time.
#Volatile
private var INSTANCE: MindValleyDatabase? = null
fun getDatabase(context: Context): MindValleyDatabase {
val tempInstance = INSTANCE
if (tempInstance != null) {
return tempInstance
}
synchronized(this) {
val instance = Room.databaseBuilder(
context.applicationContext,
MindValleyDatabase::class.java,
"mindvalley_database"
).allowMainThreadQueries()
.fallbackToDestructiveMigration().build()
INSTANCE = instance
return instance
}
}
}
}
CategoryBO.kt
#Entity(tableName = "CategoryEntity")
data class CategoryBO( #PrimaryKey(autoGenerate = true) val id:Int, val name:String)
Doa
#Dao
interface MindValleyDao {
#Query("SELECT * from CategoryEntity ORDER BY id ASC")
fun getCategories(): LiveData<List<CategoryBO>>
#Insert(onConflict = OnConflictStrategy.IGNORE)
fun insert(categoryBO: CategoryBO)
//suspend fun insert(categoryBO: CategoryBO)
#Insert(onConflict = OnConflictStrategy.IGNORE)
fun insert(categoryBOList: List<CategoryBO>)
}
I am testing it by inserting Category and fetching list of categories like
class MindValleyViewModelNew #Inject constructor() : BaseViewModel() {
var categoryList: MutableLiveData<List<CategoryBO>> = MutableLiveData()
private lateinit var mindValleyDao:MindValleyDao
fun loadDatabase(mContext:Context){
mindValleyDao = MindValleyDatabase.getDatabase(mContext).mindValleyDao()
GlobalScope.launch(Dispatchers.IO) {
mindValleyDao.insert(CategoryBO(0,"first item"))
val cats = mindValleyDao.getCategories().value
categoryList.postValue(cats)
}
}
}

mindValleyDao.getCategories() has return type is LiveData, that's why it query value async, you shouldn't call .value
LiveData type in Room should only use for observe,
If you want to get value, modify your code to fun getCategories(): List<CategoryBO> instead

Implementing Room with a viewmodel,how to get the return value of a query in DAO. instead of a List<> it just returns "CouroutineJob"

i am implementing Room with a vIewModel, my structure is the following
#DAO,#Entity,#Database,#Repository
#Entity(tableName="dx_table")
class dx_table(
#ColumnInfo(name = "name")
val naxme: String,
#PrimaryKey
#ColumnInfo(name = "phone")
val phone: String,
#ColumnInfo(name = "passx")
val passx: String,
#ColumnInfo(name = "login_fx")
val login_fx: String
)
#Dao
interface dx_dao{
#Query("SELECT * FROM dx_table")
fun get_all():LiveData<List<dx_table>>
#Insert
suspend fun insertTrx(dx_table:dx_table)
#Query("UPDATE dx_table SET login_fx =:login_fx where phone=:phonex")
suspend fun insertFx(login_fx: String,phonex: String)
#Query("SELECT * from dx_table where phone=:phonex")
suspend fun get_name_px(phonex: String):List<dx_table>
#Query("Delete from dx_table")
suspend fun deleteAll()
#Query("Select * from dx_table where login_fx=1")
suspend fun selectFx():List<dx_table>
}
#Database(entities = arrayOf(dx_table::class), version = 1, exportSchema = false)
public abstract class DxDatabase : RoomDatabase() {
abstract fun dxDao(): dx_dao
companion object {
// Singleton prevents multiple instances of database opening at the
// same time.
#Volatile
private var INSTANCE: DxDatabase? = null
fun getDatabase(context: Context): DxDatabase {
val tempInstance = INSTANCE
if (tempInstance != null) {
return tempInstance
}
synchronized(this) {
val instance = Room.databaseBuilder(
context.applicationContext,
DxDatabase::class.java,
"dx_database"
).build()
INSTANCE = instance
return instance
}
}
}
}
class dxRepository(private val dxDao: dx_dao ){
val k_d:LiveData<List<dx_table>> = dxDao.get_all()
suspend fun insert_trx(dx_table: dx_table){
dxDao.insertTrx(dx_table)
}
suspend fun insert_fx(login_fx: String,phonex: String) {
dxDao.insertFx(login_fx,phonex)
}
suspend fun select_fx() {
dxDao.selectFx()
}
suspend fun get_name_px(phonex: String) :List<dx_table> {
return dxDao.get_name_px(phonex) as List<dx_table>
}
}
The viewmodel is
class DxViewModel (application: Application) : AndroidViewModel(application) {
var repository: dxRepository
var k_d: LiveData<List<dx_table>>
init {
// Gets reference to WordDao from WordRoomDatabase to construct
// the correct WordRepository.
val dxDao = DxDatabase.getDatabase(application).dxDao()
repository = dxRepository(dxDao)
k_d = repository.k_d
}
fun insert_trx(dxTable: dx_table) = viewModelScope.launch {
repository.insert_trx(dxTable)
}
fun insert_fx(login_fx: String, phonex: String) = viewModelScope.launch {
repository.insert_fx(login_fx, phonex)
}
fun select_fx() = viewModelScope.launch {
repository.select_fx()
}
fun get_name_px(phonex: String) = viewModelScope.launch {
repository.get_name_px(phonex)
}
}
I can track the live data using observe,its not an issue, the problem i am facing is with the get_name_px(phone)
var mView = ViewModelProviders.of(this).get(DxViewModel::class.java)
var lm = mView.get_name_px(phone)
here lm seems to be job type , i need the return List , how do i get it .

In your viewModel function select_fx() return a job, because launch does not return result, so you have to either:
1) Use async and await
fun get_name_px(phonex: String) = viewModelScope.async {
repository.get_name_px(phonex)
}.await()
2) Not use launch viewModel, use it in Activity/Fragment
suspend fun get_name_px(phonex: String) = repository.get_name_px(phonex)
class CardFragment : Fragment() {
fun get() {
// launch in Dispatchers.Main
lifecycleScope.launch {
var lm = mView.get_name_px(phone)
}
// launch in background thread
lifecycleScope.launch(Dispatchers.Default) {
var lm = mView.get_name_px(phone)
}
}
}