Develop Reference

LiveData with condition

I want to use livedata in an recyclerview. But I only want to observe Livedata with a certain ID. The data gets loaded, but it doesn't update.
So here is the function in m Dao:
#Query("SELECT * FROM zutaten_table NATURAL JOIN table_ref WHERE table_ref.rezeptid = :id")
fun getZutatenforRezept(id:Int): LiveData<List<ZutatenData>>
I use a Viewmodel and a repository like this:
class LiveDataZutatenRepository(private val rezeptDao: AllDao, rezeptID: Int){
val Dao = rezeptDao
val allZutaten = Dao.getZutatenforRezept(rezeptID)
}
class SpecialZutatViewmodel(application: Application): AndroidViewModel(application){
private val repository: JustGetSpecialTypesRepository
private lateinit var repositoryLiveData: LiveDataZutatenRepository
lateinit var ZutatenforRezept : LiveData<List<ZutatenData>>
val Dao : AllDao
init {
Dao = EssenRoomDatabase.getDatabase(application, viewModelScope).allDao()
repository = JustGetSpecialTypesRepository(Dao)
}
suspend fun getRezeptWithZutat(id: Int):RezeptWithZutat{
return repository.getRezeptWithZutatFromID(id)
}
suspend fun getMengen(rezid: Int): List<RefZutatRezept>{
return repository.getMengen(rezid)
}
fun setLiveData(rezeptid: Int){
repositoryLiveData = LiveDataZutatenRepository(Dao, rezeptid )
ZutatenforRezept = repositoryLiveData.allZutaten
}
}
an in my view I use an observer to get the livedata:
val zutatViewmodel = ViewModelProvider(this).get(SpecialZutatViewmodel::class.java)
lifecycleScope.launch {
zutatViewmodel.setLiveData(rezeptid)
}
zutatViewmodel.ZutatenforRezept.observe(this, Observer { zutaten ->
zutaten?.let { adapterzut.setZutaten(it) }
})
Viewholder function:
override fun onBindViewHolder(holder: ZutatenViewHolder, position: Int) {
val current = zutaten[position]
holder.rezepteItemView.text = current.zutname
if(current.bild>=0) {
holder.rezeptePicView.setImageResource(current.bild)
holder.rezeptePicView.drawable.isFilterBitmap = false
}
}
unfortenatly the list doesn't update when the database is changed, but is loaded correctly the first time. What am I doing wrong?

it seems you are using room. So, instead of passing the entire list to the adapter, you can pass a list of all the ids in the database. Then, in the onBindViewholder, you can call the rest of the elements by using the id of the element. the code sample below might give you a better idea -
override fun onBindViewHolder(holder: PassViewHolder, position: Int) {
viewModel.getById(getItem(position)).asLiveData().observe(lifecycleOwner) {
try {
holder.bind(it)
}catch (e:Exception){
Log.e(TAG,"PassData passed = null")
e.printStackTrace()
}
}
}
I had the same problem where the views weren't getting updated but the changes where still being recorded. this method fixed it all.
the below piece of code returns the elements linked to the id as a flow.
viewModel.getById(getItem(position))
And then you covert it to live data and add an observer.
if you want, you can have a look at the project where I implemented this

DIsplay LiveData in a ListView

I have an Activity where I have a LiveData and I wanna display it in a ListView.
My code snippet:
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_records)
this.recordListView.emptyView = recordListEmptyView
viewModel = ViewModelProvider(this).get(RecordsViewModel::class.java)
recordDAO = AppDatabase.getDb(this).recordDao()
recordDAO.findAllSync().observe(this) {
//display livedata in listview after getting added
//adapter = ArrayAdapter(this,list_items,syncedRecords)
//listview.adapter = adapter
}
}
After I added a record I wanna display the records in the place where I have the comment.
I could make it work with a normal findAll() and set my adapter to the return of findAll() but I could not make it work with LiveData.
My DAO class:
#Dao
interface RecordDAO{
#Update(onConflict = REPLACE)
fun update(record:Record) : Int
#Insert(onConflict = IGNORE)
fun persist(record: Record): Long
#Delete
fun delete(record: Record): Int
#Delete
fun deleteAll(records: List<Record>)
#Query("SELECT * FROM record")
fun findAll(): List<Record>
#Query("SELECT * FROM record")
fun findAllSync(): LiveData<List<Record>>
#Query("SELECT * FROM record WHERE id = :id")
fun findById(id: Int): Record?
}

Here is how it should work. Since you did not inclue the viewmodel code, it is difficult to know the exact error. Here you observe the result of a function (recordDAO.findAllSync().observe), so I guess that the livedata is a variable only in the scope of findAllSync.
This is not how it works. Live data should be a member variable of the viewModel
class RecordsViewModel : ViewModel() {
val records = MutableLiveData<RecordDAO>()
// this function gives the records to the live data. No need for a return value
fun findAllSync() {
// Retrieve the records somehow, here this should be edited by you
records.value = someService.getRecords()
}
}
Then in the activity/fragment, you observe the live data and request a record update (You can also request the update directly from the init of the viewmodel depending on how/when you want to get the data)
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_records)
this.recordListView.emptyView = recordListEmptyView
viewModel = ViewModelProvider(this).get(RecordsViewModel::class.java)
// THIS CHANGED
viewModel.findAllSync()
viewModel.records.observe(this) { records ->
val adapter = ArrayAdapter(this,list_items, records)
listview.adapter = adapter
}
}
Note: I used a MutableLiveData. The cleaner way is to have a private MutableLiveData and a public LiveData
private val _records = MutableLiveData<RecordDAO>()
val records: LiveData<RecordDAO> = _records
The vm uses _records.value to set the data but since the Activity can only read the non mutable one, it cannot edit the value, only the viewmodel can. You don't need to do it this way it but it's always nice to know

Using the repository functions in the viewModel with coruntineScope in android Room

Working with Androind and Room for the first time, and i was able to follow a few codelabs and tutorials to achieve inserting and showing a list of my entities, but i cant seem to be able to use my other Repository methods in my ViewModel due to a type mismatch, here is my ViewModel file
class CustomerViewModel(application: Application) : AndroidViewModel(application) {
// The ViewModel maintains a reference to the repository to get data.
private val repository: CustomerRepository
// LiveData gives us updated words when they change.
val allCustomers: LiveData<List<Customer>>
init {
// Gets reference to Dao from db to construct
// the correct repo.
val customerDao = AppDatabase.getInstance(application).customerDao()
repository = CustomerRepository(customerDao)
allCustomers = repository.getCustomers()
}
fun insert(customer: Customer) = viewModelScope.launch {
repository.insert(customer)
}
}
and im trying to add a method like
fun find(id: Int) = viewModelScope.launch {
return repository.getCustomerByLocalId(id)
}
but the ide says there's a type mismatch here? Required: Customer, Found: Job
here is my repository:
class CustomerRepository(private val customerDao: CustomerDao) {
fun getCustomers(): LiveData<List<Customer>> = customerDao.getAlphabetizedCustomers()
suspend fun getCustomerByLocalId(local_Id: Int): Customer =
customerDao.customerByLocalId(local_Id)
suspend fun insert(customer: Customer) {
customerDao.insert(customer)
}
companion object {
// For Singleton instantiation
#Volatile
private var instance: CustomerRepository? = null
fun getInstance(customerDao: CustomerDao) =
instance ?: synchronized(this) {
instance ?: CustomerRepository(customerDao).also { instance = it }
}
}
}
methods in CustomerDao
#Query("SELECT * from customers ORDER BY name ASC")
fun getAlphabetizedCustomers(): LiveData<List<Customer>>
#Insert(onConflict = OnConflictStrategy.IGNORE)
suspend fun insert(customer: Customer)
#Query("SELECT * FROM customers WHERE local_id = :localId")
suspend fun customerByLocalId(localId: Int): Customer
EDIT
I tried #lena-bru 's suggestion but the error is still there, there appears to be 2 different ones, the type mismatch and that there should not be a return. are you supposed to create this method in a different location?
The IDE error

change this:
fun find(id: Int) = viewModelScope.launch {
return repository.getCustomerByLocalId(id)
}
to this:
fun find(id: Int): Customer = viewModelScope.launch {
withContext(Dispatchers.IO){
repository.getCustomerByLocalId(id)
}
}
Your find method as defined above is void, it needs to return type Customer
Also you need to provide a context, and remove the return keyword

Android app retrieve data from server, save in database and display to user

I'm rewriting an app that involves retrieving data from a server via REST, saving that to the database on each Android device, and then displaying that data to the user. The data being retrieved from the server has a "since" parameter, so it won't return all data, just data that has changed since the last retrieval.
I have the retrieval from the server working fine, but I'm not sure the best way to save that data to the database, then show it to the user. I'm using Kotlin, Retrofit, Room and LiveData.
The code below is a simplified version of what I'm actually doing, but it gets the point across.
MyData.kt (model)
#Entity(tableName = "MyTable")
data class MyData(
#PrimaryKey(autoGenerate = true)
#ColumnInfo(name = "id")
var id Int? = null,
#SerializedName("message")
#ColumnInfo(name = "message")
var message: String? = null
) {
companion object {
fun fromContentValues(values: ContentValues): MyData {
val data = MyData()
// Do this for id and message
if (values.containsKey("id") {
data.id = values.getAsInteger("id")
}
}
}
}
DataViewModel.kt
class DataViewModel(application: Application) : AndroidViewModel(application) {
private val repository = DataRepository()
fun data(since: Long) =
liveData(Dispatchers.IO) {
val data = repository.getDataFromServer(since)
emit(data)
}
fun saveData(data: List<MyData>) =
liveData(Dispatchers.Default) {
val result = repository.saveDataToDatabase(data)
emit(result)
}
fun data() =
liveData(Dispatchers.IO) {
val data = repository.getDataFromDatabase()
emit(data)
}
}
DataRepository.kt
class DataRepository(application: Application) {
// I won't add how the Retrofit client is created, it's standard
private var client = "MyUrlToGetDataFrom"
private var myDao: MyDao
init {
val myDatabase = MyDatabase.getDatabase(application)
myDao = myDatabase!!.myDao()
}
suspend fun getDataFromServer(since: Long): List<MyData> {
try {
return client.getData(since)
} catch (e: Exception) {
}
}
fun getDataFromDatabase(): List<MyData> = myDao.getAll()
suspend fun insertData(data: List<MyData>) =
myDao.insertData(data)
}
MyDao.kt
#Dao
interface PostsDao {
#Query("SELECT * FROM " + Post.TABLE_NAME + " ORDER BY " + Post.COLUMN_ID + " desc")
suspend fun getAllData(): List<MyData>
#Insert
suspend fun insertData(data: List<MyData>)
}
ListActivity.kt
private lateinit var mDataViewModel: DataViewModel
override fun onCreate(savedInstanceBundle: Bundle?) {
super.onCreate(savedInstanceBundle)
mDataViewModel = ViewModelProvider(this, DataViewModelFactory(contentResolver)).get(DataViewModel::class.java)
getData()
}
private fun getData() {
mDataViewModel.data(getSince()).observe(this, Observer {
saveData(it)
})
}
private fun saveData(data: List<MyData>) {
mDataViewModel.saveData(data)
mDataViewModel.data().observe(this, Observer {
setupRecyclerView(it)
})
}
ListActivity.kt, and possibly the ViewModel and Repository classes where it uses coroutines, are where I'm stuck. getData() retrieves the data from the server without a problem, but when it comes to saving it in the database, then taking that saved data from the database and displaying it to the user I'm unsure of the approach. As I mentioned I'm using Room, but Room will not let you access the database on the main thread.
Remember, I have to save in the database first, then retrieve from the database, so I don't want to call mDataViewModel.data().observe until after it saves to the database.
What is the proper approach to this? I've tried doing CoroutineScope on the mDataViewModel.saveData() then .invokeOnCompletion to do mDataViewModel.data().observe, but it doesn't save to the database. I'm guessing I'm doing my Coroutines incorrectly, but not sure where exactly.
It will also eventually need to delete and update records from the database.

Updated Answer
After reading comments and updated question I figured out that you want to fetch a small list of data and store it to database and show all the data stored in the database. If this is what you want, you can perform the following (omitted DataSouce for brevity) -
In PostDao You can return a LiveData<List<MyData>> instead of List<MyData> and observe that LiveData in the Activity to update the RecyclerView. Just make sure you remove the suspend keyword as room will take care of threading when it returns LiveData.
#Dao
interface PostsDao {
#Query("SELECT * FROM " + Post.TABLE_NAME + " ORDER BY " + Post.COLUMN_ID + " desc")
fun getAllData(): LiveData<List<MyData>>
#Insert
suspend fun insertData(data: List<MyData>)
}
In Repository make 2 functions one for fetching remote data and storing it to the database and the other just returns the LiveData returned by the room. You don't need to make a request to room when you insert the remote data, room will automatically update you as you are observing a LiveData from room.
class DataRepository(private val dao: PostsDao, private val dto: PostDto) {
fun getDataFromDatabase() = dao.getAllData()
suspend fun getDataFromServer(since: Long) = withContext(Dispatchers.IO) {
val data = dto.getRemoteData(since)
saveDataToDatabase(data)
}
private suspend fun saveDataToDatabase(data: List<MyData>) = dao.insertData(data)
}
Your ViewModel should look like,
class DataViewModel(private val repository : DataRepository) : ViewModel() {
val dataList = repository.getDataFromDatabase()
fun data(since: Long) = viewModelScope.launch {
repository.getDataFromServer(since)
}
}
In the Activity make sure you use ListAdapter
private lateinit var mDataViewModel: DataViewModel
private lateinit var mAdapter: ListAdapter
override fun onCreate(savedInstanceBundle: Bundle?) {
...
mDataViewModel.data(getSince())
mDataViewModel.dataList.observe(this, Observer(adapter::submitList))
}
Initial Answer
First of all, I would recommend you to look into Android Architecture Blueprints v2. According to Android Architecture Blueprints v2 following improvements can be made,
DataRepository should be injected rather than instantiating internally according to the Dependency Inversion principle.
You should decouple the functions in the ViewModel. Instead of returning the LiveData, the data() function can update an encapsulated LiveData. For example,
class DataViewModel(private val repository = DataRepository) : ViewModel() {
private val _dataList = MutableLiveData<List<MyData>>()
val dataList : LiveData<List<MyData>> = _dataList
fun data(since: Long) = viewModelScope.launch {
val list = repository.getData(since)
_dataList.value = list
}
...
}
Repository should be responsible for fetching data from remote data source and save it to local data source. You should have two data source i.e. RemoteDataSource and LocalDataSource that should be injected in the Repository. You can also have an abstract DataSource. Let's see how can you improve your repository,
interface DataSource {
suspend fun getData(since: Long) : List<MyData>
suspend fun saveData(list List<MyData>)
suspend fun delete()
}
class RemoteDataSource(dto: PostsDto) : DataSource { ... }
class LocalDataSource(dao: PostsDao) : DataSource { ... }
class DataRepository(private val remoteSource: DataSource, private val localSource: DataSource) {
suspend fun getData(since: Long) : List<MyData> = withContext(Dispatchers.IO) {
val data = remoteSource.getData(since)
localSource.delete()
localSource.save(data)
return#withContext localSource.getData(since)
}
...
}
In your Activity, you just need to observe the dataList: LiveData and submit it's value to ListAdapter.
private lateinit var mDataViewModel: DataViewModel
private lateinit var mAdapter: ListAdapter
override fun onCreate(savedInstanceBundle: Bundle?) {
...
mDataViewModel.data(since)
mDataViewModel.dataList.observe(this, Observer(adapter::submitList))
}

Android ROOM LIVEDATA not emitting the results

Hi i have a list of items that i retrieve from a data source and then i apply a map on the observable to store the data into ROOM.
It manages to add it to the table but when i try to retrieve a LiveData of it, It doesnt seem to notify my observer of the results.
There is definetly data in the table and my query works as i changed the return time from LiveData to simple a List and that worked perfectly fine
Here is my data class
#Entity
data class Item(
#PrimaryKey
val id:String,
val title: String,
val description: String,
val imgUrl: String,
val usageRules : List<String>,
)
Here is my DAO that exposes a func that add all the list of Items
#Dao
interface MyDao {
#Insert(onConflict = OnConflictStrategy.IGNORE)
fun saveAllItems(itemList: MutableList<Item>)
#Query("SELECT * FROM items")
fun getAllItems(): LiveData<MutableList<Item>>
}
My DB class
#Database(entities = arrayOf(Item::class), version = 1, exportSchema = false)
#TypeConverters(UsageRulesTypeConverter::class)
abstract class MyDatabase : RoomDatabase() {
abstract fun getProductDao(): MyDao
}
Below is how i insert data into the database:
#Inject
lateInt val database : MyDatabase
override fun getAllItems(): Single<LiveData<MutableList<Item>>> {
//retrieve new data using rertrofit
networkController.getItems().map { responseItems ->
saveAllItems(responseItems )
getItems()
}
#Transaction
fun saveAllItems(allItems: ItemsDataSource) {
database.getProductDao().saveAllItems(allItems.loadedItems)
database.getProductDao().saveAllItems(allItems.savedItems)
database.getProductDao().saveAllItems(allItems.expiredItems)
database.getProductDao().saveAllItems(allItems.unloadedItems)
}
fun getItems() : LiveData<MutableList<Item>>{
return database.getProductDao().getAllItems()
}
My data source retrieved 4 lists of Items that i then save all of them in one entity/table but LiveData doesnt notify my UI about it?
ViewModel:
override fun getUnloadedOffers(): LiveData<MutableList<ProductOffer>> {
if (!this::itemsLiveData.isInitialized) {
itemsLiveData= MutableLiveData()
//get data from network or database
itemDelegator.getItems()
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe({ items->
itemsLiveData= items
})
}
return itemsLiveData
}
UI
viewModel = ViewModelProviders.of(this, viewModelFactory).get(MyViewModel::class.java)
viewModel.getItems().observe(this, Observer {
items->
items?.let {
adapter = SomeAdapter(items)
itemsRecyclerView.adapter = adapter
adapter.notifyDataSetChanged()
}
})

Does your function getUnloadedOffers() return empty mutableList? I'm not sure if passing items to itemsLiveData is going to work, since observing LiveData is running on bg thread (if I'm not mistaken)

Try to use vararg instead of List when saving collection of data.
#Insert(onConflict = OnConflictStrategy.IGNORE)
fun saveAllItems(vararg itemList: Item)
And then you can call this method using * (also known as Spread Operator) on your list like this
saveAllItems(*responseItems.toTypedArray())