Develop Reference

How to update Room database in Android

In my application I want use MVI for application architecture and I should use Room database.
I have one activity and one fragment!
In fragment I receive data from user and save into database and in activity show this data into recyclerview.
I write below codes and my data successfully save into database!
But for show it into activity, I should exit from application and enter to show data list!
I want without exit from application, update automatically this list.
Dao codes :
#Query("SELECT * FROM my_table")
fun getAllData(): MutableList<Entity>
Repository codes:
class MyRepository #Inject constructor(private val dao: DataDao) {
fun allData() = dao.getAllData()
}
ViewModel codes:
#HiltViewModel
class MyViewModel #Inject constructor(private val repository: MyRepository) : ViewModel() {
val mainIntent = Channel<MainIntent>()
private val _state = MutableStateFlow<MainState>(MainState.Idle)
val state : StateFlow<MainState> get() = _state
init {
handleIntent()
}
private fun handleIntent() {
viewModelScope.launch {
mainIntent.consumeAsFlow().collect{
when(it){
is MainIntent.LoadAllData-> fetchingAllDataList()
}
}
}
}
private fun fetchingAllDataList() {
viewModelScope.launch {
_state.value = MainState.LoadData(repository.allData())
}
}
}
Activity codes :
lifecycleScope.launch {
//Send
viewModel.mainIntent.send(MainIntent.LoadAllData)
//Get
viewModel.state.collect { state ->
when (state) {
is MainState.Idle -> {}
is MainState.LoadData -> {
dataAdapter.setData(state.list)
fataList.apply {
layoutManager = StaggeredGridLayoutManager(2, StaggeredGridLayoutManager.VERTICAL)
adapter = noteAdapter
}
}
}
}
}
How can I fix this problem?

Several methods below can solve this problem.
Use EventBus. Send an EventBus message after saving data to database in fragment and handle this message in MyViewModel or your Activity to reload data
In your 'dao' interface, change function return type to LiveData: fun getAllData(): LiveData<MutableList<Entity>>. When related data changed in database, Room database automaticly notify changes to Observers. Check this
Use Broadcast like using EventBus
If fragment is contained in the Activity which requires the notification when data changed, use SharedViewModel to notify activity.
class MyFragment: BottomDialogSheetFragment {
var entityChangeListener: IEntityChangeListener? = null
...
// after saving data to database
entityChangeListener?.onChanged()
}
class MyActivity {
fun showDialog() {
val fragment = MyFragment()
fragment.entityChangeListener = object : IEntityChangeListener {
override fun onChanged() {
// change [fetchAllDataList] function to public
myViewModel.fetchAllDataList()
}
}
}
}
interface IEntityChangeListener {
fun onChanged()
}
// using SharedViewModel
class MyFragment: BottomDialogSheetFragment {
var entityViewModel by sharedViewModel<EntityViewModel>
...
// saving entity data
entityViewModel.saveData(entities)
}
class MyActivity {
// shared view model for entity database business
val entityViewModel by viewModels<EntityViewModel>
// viewmodel for other business logic
val viewModel by viewModels<MyViewModel>
}
class EntityViewModel: ViewModel(){
...
private val _state = MutableStateFlow<MainState>(MainState.Idle)
val state : StateFlow<MainState> get() = _state
fun fetchingAllDataList() {
viewModelScope.launch(Dispatchers.IO) {
_state.value = MainState.LoadData(repository.allData())
}
}
fun saveData(entities: List<Entity>) {
dao.save(entities)
fetchingAllDataList()
}
}

ViewModel Fragment Recreates On Screen Rotation

I'm building an application with latest android architecture components. I'm using firebase firestore as a database with jetpack navigation(Bottom nav). I'm successfully able to display data from DB. But Whenever I rotate mt screen the store fragment recreates & makes request to DB.
Repo
override fun getAllStores() = callbackFlow<State<List<Store>>> {
// Emit loading state
send(State.loading())
val listener = remoteDB.collection(Constants.COLLECTION_STORES)
.addSnapshotListener { querySnapshot, exception ->
querySnapshot?.toObjects(Store::class.java)?.let { store ->
// Emit success state with data
offer(State.success(store))
}
exception?.let {
// emit exception with message
offer(State.failed(it.message!!))
cancel()
}
}
awaitClose {
listener.remove()
cancel()
}
}.catch {
// Thrown exception on State Failed
emit(State.failed(it.message.toString()))
}.flowOn(Dispatchers.IO)
ViewModel
#ExperimentalCoroutinesApi
#InternalCoroutinesApi
class StoreViewModel(private val repository: DBInterface = Repo()) : ViewModel() {
fun getAllStores() = repository.getAllStores()
}
Store Fragment
#ExperimentalCoroutinesApi
#InternalCoroutinesApi
class StoreFragment : Fragment(R.layout.fragment_store) {
private lateinit var storeAdapter: StoreAdapter
private val viewModel: StoreViewModel by viewModels()
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
(activity as MainActivity).supportActionBar?.title = getString(R.string.store_title)
setUpRV()
// get all stores
lifecycleScope.launch {
getAllStores()
}
}
private suspend fun getAllStores() {
viewModel.getAllStores().collect { state ->
when (state) {
is State.Loading -> {
store_progress.show()
}
is State.Success -> {
storeAdapter.differ.submitList(state.data)
store_progress.animate().alpha(0f)
.withEndAction {
store_rv.animate().alpha(1f)
store_progress.hide()
}
}
is State.Failed -> {
store_progress.hide()
activity?.toast("Failed! ${state.message}")
}
}
}
}
private fun setUpRV() {
storeAdapter = StoreAdapter()
store_rv.apply {
adapter = storeAdapter
addItemDecoration(SpacesItemDecorator(16))
}
}
}
Main activity(Nav graph)
#InternalCoroutinesApi
#ExperimentalCoroutinesApi
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
setSupportActionBar(toolbar)
// init bottom navigation
bottom_navigation.setupWithNavController(nav_host_fragment.findNavController())
}
}
Every time it recreates my fragment. I don't want to save or retain any views using methods. Because ViewModel used to protect view on screen rotation. Kindly let me know any tips & tricks. Thanks in advance ;)

Flow in itself is not stateful - that is a key difference between it and LiveData. That means that after your collect completes, the next collect starts the callbackFlow from scratch.
This is precisely why the lifecycle-livedata-ktx artifact contains the asLiveData() extension that allows you to continue to use a Flow at the repository layer while maintaining the stateful (and Lifecycle) properties of LiveData for your UI:
#ExperimentalCoroutinesApi
#InternalCoroutinesApi
class StoreViewModel(private val repository: DBInterface = Repo()) : ViewModel() {
fun getAllStores() = repository.getAllStores().asLiveData()
}
You'd change your UI code to continue to use LiveData and observe().
Kotlin is working on a shareIn operation that would allow your ViewModel to save the state of a Flow. That would allow you to use Flow at all layers of your app without requerying information from scratch when the Fragment/Activity that is calling collect gets destroyed and recreated.

you can add android:configChanges="orientation|screenSize|screenLayout" to your manifest for the activity. this should prevents restarts when orientation changes.
check this site and also here are som infos.

MutableLiveData ArrayList is empty even after postValue() Kotlin

I am now stuck and currently wondering why my mutable arraylist returns null even if it is being updated with postvalue(). I tried to display it using Toast and it displayed [] which I think is null. It had no space in between so it looked like a box. I did toString() it as well in order to show the text. How would I be able to solve this problem?
Here is my Main Activity:
val list = ArrayList<String>()
list.add("text1")
list.add("text2")
val viewmodel = ViewModelProviders.of(this).get(viewmodel::class.java)
viewmodel.Testlist.postValue(list)
ViewModel:
class viewmodel: ViewModel() {
val Testlist: MutableLiveData<ArrayList<String>> = MutableLiveData()
init {
Testlist.value = arrayListOf()
}
}
Fragment:
Top area:
activity?.let {
val viewmodel = ViewModelProviders.of(this).get(viewmodel::class.java)
observeInput(viewmodel)
}
Bottom area:
private fun observeInput(viewmodel: viewmodel) {
viewmodel.Testlist.observe(viewLifecycleOwner, Observer {
it?.let {
Toast.makeText(context, it.toString(), Toast.LENGTH_LONG).show()
}
})
}

You post the value to the LiveData object in the activity's viewmodel, which isn't the same instance as the fragment's viewmodel. Let's take look at the way you instantiate the viewmodel in your fragment:
activity?.let {
// activity can be refered by the implicit parameter `it`
// `this` refers to the current fragment hence it's the owner of the view model
val viewmodel = ViewModelProviders.of(this).get(viewmodel::class.java)
observeInput(viewmodel)
}
To get a viewmodel that is shared between your activity and fragment you have to pass the activity as its owner:
activity?.let { val viewmodel = ViewModelProviders.of(it).get(viewmodel::class.java) }

Probably you can see developer guide example to resolve your problem
https://developer.android.com/topic/libraries/architecture/viewmodel.html#kotlin
// shared viewmodel
class SharedViewModel : ViewModel() {
private val usersList: MutableLiveData<List<String>>()
fun getUsers(): LiveData<List<String>> {
return usersList
}
fun setUsers(users: List<String>) {
usersList.value = users
}
}
// Attach ViewModel In Activity onCreate()
val model = ViewModelProviders.of(this)[SharedViewModel::class.java]
val list = arrayListOf<String>()
list.add("user1")
list.add("user2")
model.setUsers(list)
// Get same ViewModel instance In fragment onCreateView()
model = activity?.run {
ViewModelProviders.of(this)[SharedViewModel::class.java]
} ?: throw Exception("Invalid Activity")
model.getUsers().observe(this, Observer<List<User>>{ users ->
// update UI
})

You can use this :
fun <T : Any?> MutableLiveData<ArrayList<T>>.default(initialValue: ArrayList<T>) = apply { setValue(initialValue) }
and then use this function as below:
viewmodel.Testlist.default(ArrayList())
For me, I have a BaseActivity that other activities extend from it :
class UAppCompatActivity : AppCompatActivity() {
protected fun <T : Any?> MutableLiveData<ArrayList<T>>.default(initialValue: ArrayList<T>) = apply { setValue(initialValue) }
protected fun <T> MutableLiveData<ArrayList<T>>.addItem(item: T) {
val updatedItems = this.value as ArrayList
updatedItems.add(item)
this.value = updatedItems
}
protected fun <T> MutableLiveData<ArrayList<T>>.deleteItem(item: T) {
val updatedItems = this.value as ArrayList
updatedItems.remove(item)
this.value = updatedItems
}
...

have you used the same instance of your view model? or have you defined another view model in the fragment class? The issue could be that you're accessing a different instance of the view model and not the one were the MutableLiveData was updated

Hold data from EventListener in MutableLiveData

I'm trying to retrive data from firestore and want to keep it in shared view model. Basically I have a main activity and 2 fragments that need to retrieve data from shared view model of main activity. My current method is :
class SharedViewModel: ViewModel() {
private val firebaseUtils = FirebaseUtils()
fun getTempWords(localeLearn: String): LiveData<DocumentSnapshot> {
val document = firebaseUtils.getTempWordsLocaleRef(localeLearn)
return FirebaseDocumentLiveData(document)
}}
What i want is that just retrive data once and keep it in MutableLiveData and pass to fragmetns.
Edit:
What I'm done is:
var tempWords : MutableLiveData<DocumentSnapshot> = MutableLiveData()
fun getTemp(localeLearn: String): LiveData<DocumentSnapshot> {
if (tempWords.value == null) {
val document = firebaseUtils.getTempWordsLocaleRef(localeLearn)
tempWords = FirebaseDocumentLiveData(document)
}
return tempWords
}
But if i kill the fragment and recreate it again, it calls EventListener in FirebaseDocumentLiveData(document) class again.
Edit 2:
My Fragment
private lateinit var model: SharedViewModel
override fun onCreate(savedInstanceState: Bundle?) {
//
model = activity?.run {
ViewModelProviders.of(this).get(SharedViewModel::class.java)
} ?: throw Exception("Invalid Activity")
}
//
model.getTemp(mLocaleLearn!!).observe(this, Observer {...}

What is the question? it looks like you successfully made it.
You ask how you can access the data from your fragments?
in view model class
private final MutableLiveData<Item> data = new MutableLiveData<Item>();
in your fragments:
model = ViewModelProviders.of(getActivity()).get(SharedViewModel.class);

Receiving data in incorrect order on Querying database

Activity receiving intent
class AddNoteActivity : AppCompatActivity() {
private lateinit var addViewModel: NoteViewModel
private lateinit var titleEditText: TextInputEditText
private lateinit var contentEditText: TextInputEditText
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_add_note_activty)
setSupportActionBar(toolbar)
addViewModel = ViewModelProviders.of(this).get(NoteViewModel::class.java)
titleEditText = findViewById(R.id.itemTitle)
contentEditText = findViewById(R.id.itemNote)
val extra = intent.extras
if (extra != null) {
val uuid = extra.getLong("UUID")
val note: Notes? = addViewModel.getNote(uuid)
titleEditText.setText(note!!.title)
contentEditText.setText(note.note)
}
}
}
NoteViewModel class
class NoteViewModel(application: Application) : AndroidViewModel(application) {
companion object {
private var note: Notes = Notes(0, "", "test title", "test ontent")
}
fun getNote(uuid: Long?): Notes {
val job = async(CommonPool) {
getNoteAsyncTask(notesDatabase).execute(uuid)
}
runBlocking { job.await() }
return note
}
class getNoteAsyncTask(database: NotesDatabase) : AsyncTask<Long, Unit, Unit>() {
private val db: NotesDatabase = database
override fun doInBackground(vararg params: Long?) {
note = db.notesDataDao().getNote(params[0])
}
}
}
If I pass an intent to get a Note object from the database with a uuid and set that received data in titleEditText and contentEditText, the data set in the Note was from previous intent invoked when we clicked on the Note item in RecyclerView. On clicking the Note item for the first time, I get the default value which I have set "test title" and "test content".
Aforementioned is the behavior most of the time. Sometimes the data set in titleEditText and contentEditText is of the correct Note object.
Can someone please tell me what I have done wrong? How can I correct my apps behavior?

Unfortunately, there is a big mistake in how you use a view model to provide a data to your view(AddNoteActivity).
Basically, your view never has a chance to wait for the data to be fetched as it always receives a default value. This happens because the AsyncTask runs on its own thread pool so the coroutine completes immediately and returns a default value.
You should consider using LiveData to post a new object to your view and refactor your view model.
So, you need to make a query to the database synchronous and observe changes to a note rather than have a getter for it. Of course, in a real life scenario it might be a good idea to have different kind of states to be able to show a spinner while a user is waiting. But this is another big question. So to keep things simple consider changing your view model to something like that:
class NoteViewModel(private val database: NotesDatabase) : ViewModel { // you do not need an application class here
private val _notes = MutableLiveData<Notes>()
val notes: LiveData<Notes> = _notes
fun loadNotes(uuid: Long) {
launch(CommonPool) {
val notes = database.notesDataDao().getNote(uuid)
_notes.setValue(notes)
}
}
}
Then, you can observe changes to the note field in your activity.
class AddNoteActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
// ...
val noteViewModel = ViewModelProviders.of(this).get(NoteViewModel::class.java)
noteViewModel.notes.observe(this, Observer {
title.text = it.title
content.text = it.note
})
}
}
Also you need to use a ViewModelProvider.Factory to create your view model and properly inject dependencies into it. Try to avoid having a context there as it makes it much harder to test.